Earthquake focal mechanism forecasting in Italy for PSHA purposes

Earthquake focal mechanism forecasting in Italy for PSHA purposes SUMMARY In this paper, we put forward a procedure that aims to forecast focal mechanism of future earthquakes. One of the primary uses of such forecasts is in probabilistic seismic hazard analysis (PSHA); in fact, aiming at reducing the epistemic uncertainty, most of the newer ground motion prediction equations consider, besides the seismicity rates, the forecast of the focal mechanism of the next large earthquakes as input data. The data set used to this purpose is relative to focal mechanisms taken from the latest stress map release for Italy containing 392 well-constrained solutions of events, from 1908 to 2015, with Mw ≥ 4 and depths from 0 down to 40 km. The data set considers polarity focal mechanism solutions until to 1975 (23 events), whereas for 1976–2015, it takes into account only the Centroid Moment Tensor (CMT)-like earthquake focal solutions for data homogeneity. The forecasting model is rooted in the Total Weighted Moment Tensor concept that weighs information of past focal mechanisms evenly distributed in space, according to their distance from the spatial cells and magnitude. Specifically, for each cell of a regular 0.1° × 0.1° spatial grid, the model estimates the probability to observe a normal, reverse, or strike-slip fault plane solution for the next large earthquakes, the expected moment tensor and the related maximum horizontal stress orientation. These results will be available for the new PSHA model for Italy under development. Finally, to evaluate the reliability of the forecasts, we test them with an independent data set that consists of some of the strongest earthquakes with Mw ≥ 3.9 occurred during 2016 in different Italian tectonic provinces. Europe, Earthquake ground motions, Earthquake interaction, forecasting, and prediction, Seismicity and tectonics, Statistical seismology 1 INTRODUCTION Probabilistic seismic hazard analysis (PSHA) is based on the forecast of seismicity in the next decades (the seismicity rate models) coupled with the use of ground motion prediction equations (GMPEs) to estimate the ground shaking caused by the expected earthquakes. The link between seismicity rate models and GMPEs is not always straightforward, because many common seismicity rate models estimate the expected number of earthquakes in each space and magnitude bin, while the most recent GMPEs need additional information, such as, for example, the expected style of faulting. This lack of information may affect PSHA, where a reasonable set of different seismicity rate models and GMPEs has to be considered altogether to quantify and to model the so-called epistemic uncertainty (Marzocchi et al.2015). For instance, the new ongoing seismic hazard model for Italy is planning to consider a set of seismicity rate models and different GMPEs, but most of the seismicity rate models do not provide a forecast of the style of faulting (Meletti et al.2017). Motivated by this lack, in this paper, we propose a forecast of the earthquake focal mechanism in Italy, from which the style of faulting and possibly the geometry of the expected ruptures may be derived. This forecasting model is built independently from the seismicity rate models, hence it can be easily coupled with the outcome of any seismicity rate model that does not provide such a kind of information. Eventually, this forecast is going to facilitate the use of all GMPEs with all seismicity rate models for PSHA purposes. Although we focus our attention on the Italian region, the adopted procedure is quite general, and it can be applied to any other country or geographical region. Italy is characterized by complex tectonics, which leads to a large spatial variability of the observed style of faulting. Although information of different nature is available to characterize the tectonics variability, in this paper we aim to forecast the focal mechanism of future earthquakes, and so, we use only the focal mechanisms of past earthquakes under the assumption that the main tectonic features remain stable over decades. The focal mechanism forecast for future large earthquakes is based on a procedure developed by Selva & Marzocchi (2004), which was inspired by the concept of total moment tensor proposed by Kostrov (1974). In the next sections, we briefly introduce the Italian tectonics setting and then describe, in detail, the data set used and the methodology. Finally, we show and discuss the results in comparison to the main Italian tectonic features in order to evaluate the quality of produced results. 2 ITALIAN TECTONIC SETTING The geodynamic setting of the Italian region is characterized by a complex interaction of different mechanisms, mainly related to the continental collision between Africa and Eurasia plates and by the presence of smaller intervening microplates (Fig. 1). A fundamental role has been played by Adria microplate that has complicated and influenced the tectonic processes, the distribution of seismicity and also the volcanic activity. In this convergence context, which is going on since the Early Tertiary, an Adriatic-Ionian lithosphere subduction beneath the Alps (to the north), Dinarides (to the east) and Apennines (to the west) has developed (Malinverno & Ryan 1986; Royden et al.1987; Ghisetti & Vezzani 1999; Faccenna et al.2001; Scrocca et al.2003). Figure 1. View largeDownload slide Tectonic sketch map of Italy with main thrust, normal and strike-slip faults (modified after Meletti et al.2000). In particular, letters in ‘bold’ indicates the epicentres of the 2016 strongest earthquakes (Mw ≥ 3.9) used as testing data (see also Table 4 and Fig. 7). Figure 1. View largeDownload slide Tectonic sketch map of Italy with main thrust, normal and strike-slip faults (modified after Meletti et al.2000). In particular, letters in ‘bold’ indicates the epicentres of the 2016 strongest earthquakes (Mw ≥ 3.9) used as testing data (see also Table 4 and Fig. 7). The actual mechanisms linked to the subduction process and to the complex slab geometry beneath the Apennines are still debated (Carminati & Doglioni 2012), including slab sinking (Mitrovica et al.1989), slab rollback (Carminati et al.2003; Carminati & Doglioni 2012), slab break off (Wortel & Spakman 2000) and slab-induced return flow (Faccenna & Becker 2010). In particular, as documented by tomography and also suggested by the absence of intermediate/deep seismicity, at depth the Adriatic slab is no longer intact: in the central and southern Apennines, the lithospheric slab is likely detached and the subduction has ended (Amato et al.1993; Lucente et al.1999; Wortel & Spakman 2000; De Gori et al.2001; Cimini & Marchetti 2006; Di Stefano et al. 2009). On the contrary, clear evidence of an oceanic slab is well documented by the occurrence of intermediate and deep seismicity beneath the southern Tyrrhenian basin with earthquakes located along a narrow 200-km-wide Benioff zone. The present-day regional geodynamic setting is then mainly characterized by the relation occurring between subduction and backarc extension (Karig 1971) and by the eastward/south-eastward rollback of the slab that led to the development of the thrust belt-foredeep Apennine system (among many others: Malinverno & Ryan 1986; Royden et al.1987; Patacca & Scandone 1989; Doglioni 1991; Carminati et al.2002; Faccenna et al.2003; Di Stefano et al.2009). The eastward migrating subduction hinge with the progressive retreat of the slab produced compression at the outer front and contemporaneous extension in the backarc Tyrrhenian region (e.g. Selvaggi & Amato 1992; Frepoli & Amato 1997; Lucente et al.1999; Cimini & Marchetti 2006). In the northern Apennines, the extension compression pair—eastward migrating from late Miocene—is still observable (e.g. Lavecchia et al.1994; Frepoli & Amato 1997; Mariucci et al.1999), whereas in the central-southern Apennines a prevailing extension is evident, at least since middle Pleistocene (e.g. Meletti et al.2000). Such a complex tectonic setting represents a challenge to provide reliable focal mechanism forecasts for the next earthquakes. 3 DATA AND METHOD 3.1 Input data: focal mechanisms and gridding The latest Italian data set of the contemporary stress field in the crust consists of 855 stress indicators: single earthquake focal mechanisms, data from formal inversion of earthquake focal mechanisms, borehole breakouts, mapped active faults and overcoring data (Montone & Mariucci 2016; Mariucci & Montone 2017). Each datum is quality-ranked according to the World Stress Map Project rules (http://www.world-stress-map.org; Heidbach et al.2010), from A the best to D the worst. ‘A’ quality means that the orientation is believed to be within ±15°, ‘B’ ±15°–20°, ‘C’ ±20°–25°, ‘D’ ±25–40° (a questionable orientation) and quality ‘E’ denotes unreliable information (>40°). Among all stress indicators currently available for Italy, in this work we select and use only the focal mechanism data, because they are more suitable for the purpose of this paper. Such focal mechanisms are taken from the latest stress map release for Italy (Montone & Mariucci 2016) which contains 392 well-constrained (C quality data) solutions of events (see Fig. 2), from 1908 to 2015, with Mw ≥ 4 and depths within the uppermost 40 km (85 per cent of hypocentres with depth ≤ 20 km). For the period 1908–1975, the data set considers polarity focal mechanism solutions (only 23 events), whereas for 1976–2015, it takes into account only the Centroid Moment Tensor (CMT)-like earthquake focal solutions for data homogeneity (European-Mediterranean Regional Centroid Moment Tensor database, http://www.bo.ingv.it/RCMT/; and ‘The Italian CMT dataset from 1976 to the present’, http://www.bo.ingv.it/RCMT/, Pondrelli et al.2006). Figure 2. View largeDownload slide Location map of 392 Mw ≥ 4 focal mechanisms (training data) split in 179 NF, 128 TF and 85 SS (red, blue and green lower hemisphere focal mechanisms, respectively), from 1908 to 2015. The grey points indicate the 8993 centres of the cells where the TWMTs have been computed. Black lines represent the main tectonic structures (DISS Working Group 2015). Figure 2. View largeDownload slide Location map of 392 Mw ≥ 4 focal mechanisms (training data) split in 179 NF, 128 TF and 85 SS (red, blue and green lower hemisphere focal mechanisms, respectively), from 1908 to 2015. The grey points indicate the 8993 centres of the cells where the TWMTs have been computed. Black lines represent the main tectonic structures (DISS Working Group 2015). At first approximation the elastic strain can be considered directly related to stress and the P, B and T axes are assumed to be equal to σ1, σ2 and σ3, respectively (e.g. Zoback & Zoback 1980). Assuming one of the three principal stresses as vertical, the other two lie on the horizontal plane and are defined as maximum and minimum horizontal stress (SHmax and Shmin), according to their relative magnitude. SHmax corresponds to σ1 [thrust (TF) and strike-slip faulting (SS) regime] or σ2 [normal faulting (NF) regime]. The principle axes of the derived moment tensor (compression P, null B and extension T) fully describe the focal mechanisms. Regional compilations of earthquake focal mechanisms show that the average orientation for compression (P), null (B) and extension (T) axes provides a good indication of the stress orientation along a region (e.g. Zoback & Zoback 1980). In order to identify the tectonic regime (according to Anderson 1951), we use a classification criterion related to the plunge of the P, T and B axes (see table 3 in Zoback 1992), discarding all the focal solutions with P, T and B axes that do not define a clear tectonic regime. We group the data into the three main tectonic regime categories: NF, TF and SS to perform our calculations for each group separately. The few ‘oblique’ focal mechanisms (17), classified with an intermediate regime (normal strike, NS and thrust strike, TS), are redistributed into the three main categories on the basis of the maximum plunge of the axes, considering that the vertical axis is P/σ1 for NF, T/σ3 for TF and B/σ2 for SS and also taking into account the most geologically plausible criterion. After this classification, our training data set consists of 179 NF, 128 TF and 85 SS faulting focal mechanisms (see Tables 1–3). Fig. 2 shows the location map and types of focal mechanisms as normal (red), thrust (blue) and strike-slip (green) lower hemisphere focal mechanisms, respectively. Table 1. List of 179 earthquakes selected as input data and classified as normal faulting focal mechanisms (NF, red lower hemisphere focal mechanisms in Fig. 2). Date  Lat (°)  Lon (°)  Depth (km)  Mw  Strike1 (°)  Dip1 (°)  Rake1 (°)  Strike2 (°)  Dip2 (°)  Rake2 (°)  1908 December 28  38.12  15.60  10.0  7.0  349  42  − 122  209  55  − 64  1915 January 13  41.99  13.65  8.0  6.9  135  63  − 90  315  26  − 89  1930 July 23  41.05  15.36  15.0  6.7  280  50  − 80  84  41  − 101  1939 February 11  44.07  11.65  7.0  4.7  310  49  − 120  171  49  − 60  1939 October 15  44.23  10.20  27.0  4.9  175  26  − 126  33  69  − 74  1941 March 16  38.44  12.12  20.0  6.9  217  39  − 76  19  52  − 101  1958 June 24  42.35  13.44  10.0  5.0  22  37  − 57  162  59  − 112  1962 August 21  41.13  14.95  8.0  5.7  310  65  − 130  201  54  − 31  1962 August 21  41.08  15.00  8.0  6.1  310  65  − 110  186  41  − 40  1967 December 09  42.00  16.50  33.0  4.7  277  74  − 90  97  15  − 89  1971 February 06  42.31  11.76  2.0  4.6  279  44  − 133  151  59  − 56  1971 February 12  43.23  12.49  33.0  4.5  290  48  − 139  169  60  − 50  1974 December 02  42.82  12.93  5.0  4.8  195  48  − 44  317  58  − 128  1977 June 05  37.88  14.46  10.0  4.6  61  26  − 139  293  73  − 70  1978 March 11  38.10  16.03  33.0  5.2  270  41  − 72  66  52  − 105  1978 July 30  42.65  12.46  10.0  4.4  209  42  − 55  345  57  − 117  1979 September 19  42.81  13.06  16.0  5.8  183  28  − 70  341  64  − 100  1980 February 20  39.30  16.21  12.0  4.3  14  43  − 78  178  48  − 101  1980 March 09  39.94  16.12  19.0  4.7  157  35  − 80  324  56  − 97  1980 May 14  40.46  15.85  24.0  4.8  119  38  − 112  326  56  − 74  1980 June 07  44.09  10.72  16.0  4.6  334  23  − 50  112  72  − 105  1980 June 09  42.29  13.88  20.0  4.7  266  37  − 88  84  53  − 91  1980 June 14  41.85  13.73  8.0  5.0  296  37  − 90  116  53  − 90  1980 November 23  40.91  15.37  10.0  6.9  135  41  − 80  303  50  − 98  1980 November 24  40.89  15.26  10.0  5.0  131  29  − 110  333  63  − 79  1980 November 25  40.70  15.47  10.0  4.9  129  26  − 65  281  67  − 102  1980 November 25  40.65  15.40  10.0  5.4  122  30  − 119  335  64  − 74  1981 January 16  40.95  15.37  15.0  5.2  115  30  − 93  298  60  − 89  1981 November 29  40.74  15.64  33.0  4.5  104  41  − 138  340  64  − 58  1982 March 21  39.70  15.64  18.9  5.2  15  39  − 127  239  60  − 64  1982 August 15  40.81  15.36  10.0  4.7  158  48  − 45  282  59  − 128  1982 October 17  43.12  12.59  13.0  4.6  132  39  − 125  354  59  − 65  1982 October 17  43.16  12.59  16.0  4.6  137  34  − 128  0  64  − 68  1982 October 18  43.13  12.63  19.0  4.6  143  27  − 131  8  70  − 71  1983 August 12  41.75  13.85  10.0  4.8  104  46  − 115  318  49  − 66  1984 April 22  43.62  10.19  15.0  4.6  349  38  − 67  141  56  − 107  1984 April 29  43.27  12.57  14.0  5.6  143  21  − 72  304  70  − 97  1984 May 07  41.77  13.89  10.0  5.9  174  31  − 52  312  66  − 110  1984 May 11  41.83  13.95  13.0  5.5  156  43  − 76  317  49  − 103  1986 October 01  44.34  10.19  28.0  4.5  135  43  − 91  316  47  − 90  1987 January 28  40.95  15.47  10.0  4.5  160  45  − 79  326  46  − 100  1987 July 05  43.78  12.23  11.0  4.5  298  43  − 83  108  48  − 97  1988 January 08  40.08  16.01  10.0  4.7  148  30  − 86  324  60  − 92  1993 June 05  43.12  12.68  8.0  4.6  139  37  − 108  341  55  − 77  1995 August 24  44.13  10.76  34.0  4.5  117  47  − 111  327  47  − 69  1996 April 03  40.76  15.49  10.0  4.9  123  30  − 110  325  62  − 79  1996 October 20  42.60  13.28  10.0  4.3  128  31  − 119  341  63  − 74  1996 December 14  37.81  13.84  40.0  4.3  123  23  − 43  254  74  − 108  1997 March 19  41.40  14.63  10.0  4.5  280  27  − 110  122  65  − 80  1997 September 03  43.01  12.90  10.2  4.5  137  30  − 88  315  60  − 91  1997 September 26  43.02  12.89  10.0  5.7  321  44  − 98  152  46  − 83  1997 September 26  43.03  12.85  10.0  6.0  144  42  − 80  312  49  − 98  1997 September 26  43.01  12.97  10.0  4.5  147  29  − 88  325  61  − 91  1997 September 26  43.06  12.85  10.0  4.3  193  45  − 43  316  61  − 126  1997 September 27  43.09  12.81  5.5  4.3  326  35  − 92  148  55  − 89  1997 September 27  43.02  12.83  10.0  4.2  288  36  − 135  160  66  − 63  1997 September 27  43.06  12.77  10.0  4.3  136  35  − 80  304  56  − 97  1997 October 02  43.64  12.14  10.0  4.4  158  41  − 58  298  56  − 115  1997 October 03  43.03  12.84  10.0  5.2  141  43  − 74  300  49  − 104  1997 October 04  42.90  12.90  10.0  4.4  299  42  − 101  133  49  − 81  1997 October 04  42.93  12.86  10.0  4.4  322  33  − 52  99  64  − 112  1997 October 04  42.94  12.93  10.0  4.7  318  42  − 80  125  49  − 99  1997 October 04  42.93  12.90  10.0  4.4  329  43  − 77  131  48  − 102  1997 October 06  43.02  12.84  10.0  5.4  145  40  − 80  312  51  − 98  1997 October 07  42.99  12.82  11.6  4.2  126  26  − 102  319  65  − 84  1997 October 07  43.03  12.85  10.0  4.5  141  42  − 77  304  49  − 101  1997 October 12  42.91  12.94  10.0  5.2  321  40  − 100  154  51  − 82  1997 October 12  42.86  12.97  10.0  4.3  271  14  − 133  136  80  − 80  1997 October 13  42.90  13.00  10.0  4.3  315  37  − 73  115  54  − 102  1997 October 13  42.89  12.92  10.0  4.4  305  35  − 96  133  56  − 86  1997 October 14  42.93  12.92  10.0  5.6  122  38  − 100  314  52  − 82  1997 October 15  42.93  12.89  10.0  4.4  329  40  − 65  117  55  − 110  1997 October 16  42.91  12.92  10.0  4.3  310  11  − 80  120  79  − 92  1997 October 16  42.98  12.89  10.0  4.1  118  35  − 88  295  55  − 92  1997 October 16  42.88  12.97  10.0  4.3  305  33  − 123  163  63  − 70  1997 October 17  42.89  12.91  10.0  4.2  326  48  − 53  97  54  − 124  1997 October 19  42.97  12.79  10.0  4.2  128  44  − 103  326  47  − 78  1997 October 25  42.84  13.01  10.0  4.3  333  33  − 54  112  64  − 111  1997 November 09  42.87  13.00  10.0  4.9  118  46  − 113  329  48  − 68  1997 November 30  42.88  12.95  10.0  4.3  125  36  − 119  339  59  − 70  1997 December 24  44.09  10.55  10.0  4.3  95  49  − 132  329  56  − 53  1997 December 31  42.87  12.99  10.0  4.3  293  35  − 135  164  66  − 64  1998 February 07  43.00  12.90  10.2  4.4  308  36  − 98  138  55  − 84  1998 March 21  42.90  12.90  10.0  5.0  137  15  − 97  325  75  − 88  1998 April 03  43.16  12.70  10.0  5.1  142  30  − 106  341  61  − 81  1998 April 03  43.23  12.67  10.0  4.3  152  33  − 108  352  59  − 79  1998 April 05  43.18  12.76  10.0  4.8  138  31  − 98  327  59  − 85  1998 June 02  43.17  12.73  10.0  4.3  311  42  − 124  173  56  − 63  1998 June 25  43.00  12.80  10.0  4.0  96  47  − 123  319  52  − 60  1998 August 15  42.41  12.98  10.0  4.4  298  26  − 52  76  70  − 107  1998 September 09  40.03  15.98  10.0  5.6  139  29  − 83  311  61  − 94  1999 February 14  38.17  15.06  33.0  4.7  18  39  − 108  220  53  − 76  1999 July 07  44.29  10.90  10.0  4.7  314  40  − 44  80  64  − 121  1999 October 10  42.67  13.19  10.0  4.2  348  50  − 47  112  55  − 129  1999 December 29  46.60  10.31  10.0  4.8  320  43  − 99  152  47  − 82  1999 December 31  46.60  10.32  10.0  4.1  13  34  − 45  143  67  − 116  2000 April 01  42.89  11.74  10.0  4.5  309  38  − 49  81  63  − 117  2000 April 06  46.60  10.33  5.0  4.0  359  47  − 64  144  49  − 115  2000 August 21  44.87  8.48  10.0  4.9  146  39  − 71  302  53  − 105  2000 October 03  44.27  10.80  10.0  4.2  317  24  − 105  153  67  − 83  2000 December 16  42.65  12.66  10.0  4.2  273  35  − 76  76  56  − 100  2001 October 18  39.10  16.61  10.0  4.3  332  44  − 88  149  46  − 92  2001 November 25  37.91  13.96  20.0  4.7  137  31  − 57  280  64  − 108  2001 November 26  43.60  12.10  10.0  4.7  358  21  − 72  158  70  − 97  2002 February 21  43.76  12.05  7.0  4.1  313  35  − 86  128  55  − 93  2002 April 18  40.69  15.58  10.0  4.5  329  13  − 72  131  77  − 94  2003 January 26  43.88  11.96  6.0  4.7  140  41  − 101  336  50  − 80  2003 January 26  43.88  11.95  7.0  4.5  291  37  − 130  158  62  − 64  2005 April 18  44.71  9.35  0.0  4.0  336  34  − 35  96  71  − 118  2006 February 27  38.15  15.20  9.0  4.4  22  24  − 95  208  66  − 88  2006 April 17  43.64  10.23  10.0  4.2  323  50  − 53  94  52  − 125  2006 December 19  37.78  14.91  23.0  4.2  18  16  − 40  147  80  − 102  2007 August 18  38.22  15.17  12.0  4.5  347  34  − 120  201  61  − 71  2007 October 21  42.38  12.97  10.0  4.2  330  31  − 44  100  69  − 113  2008 March 01  44.06  11.25  10.0  4.7  278  36  − 123  136  60  − 68  2008 March 01  44.35  11.49  10.0  4.0  318  32  − 108  160  60  − 79  2008 March 01  44.06  11.22  5.0  4.2  326  43  − 67  116  51  − 110  2008 April 08  39.16  16.66  10.0  4.4  235  49  − 35  350  64  − 134  2008 October 24  44.34  7.36  10.0  4.1  308  51  − 150  198  67  − 43  2009 March 30  42.33  13.36  11.0  4.4  2  35  − 70  158  57  − 104  2009 April 05  42.36  13.37  10.0  4.2  147  37  − 108  349  55  − 77  2009 April 06  42.33  13.33  10.0  6.3  326  35  − 80  134  56  − 97  2009 April 06  42.41  13.32  10.0  5.1  355  46  − 53  128  55  − 122  2009 April 06  42.38  13.34  10.0  4.5  340  25  − 103  175  66  − 84  2009 April 06  42.35  13.37  10.0  4.2  138  41  − 93  323  49  − 87  2009 April 06  42.36  13.33  10.0  4.4  348  40  − 64  135  55  − 111  2009 April 06  42.45  13.36  10.0  5.1  341  44  − 68  132  50  − 109  2009 April 07  42.34  13.39  10.0  5.1  341  41  − 64  128  54  − 111  2009 April 07  42.28  13.46  15.0  5.5  105  53  − 134  342  55  − 48  2009 April 07  42.38  13.38  10.0  4.5  321  41  − 64  108  54  − 110  2009 April 08  42.30  13.43  10.0  4.0  344  38  − 84  156  52  − 95  2009 April 08  42.51  13.36  10.0  4.1  319  40  − 76  121  51  − 101  2009 April 09  42.48  13.34  15.0  5.4  329  45  − 81  136  46  − 99  2009 April 09  42.50  13.36  17.0  5.2  321  44  − 83  132  46  − 97  2009 April 09  42.44  13.42  10.0  4.3  113  57  − 144  2  61  − 39  2009 April 13  42.50  13.36  10.0  5.0  337  38  − 71  133  54  − 104  2009 April 14  42.53  13.28  10.0  4.0  309  42  − 92  132  48  − 88  2009 April 15  42.54  13.28  10.0  4.1  113  33  − 126  333  64  − 69  2009 April 23  42.25  13.49  10.0  4.1  126  43  − 105  326  49  − 76  2009 April 23  42.23  13.48  10.0  4.3  323  27  − 95  149  63  − 87  2009 June 22  42.45  13.36  14.0  4.7  113  19  − 112  315  72  − 83  2009 July 03  42.41  13.39  10.0  4.1  144  42  − 108  348  50  − 74  2009 July 12  42.34  13.38  10.0  4.3  342  35  − 76  146  56  − 99  2009 September 24  42.45  13.33  10.0  4.2  184  35  − 76  347  56  − 100  2009 November 08  37.83  14.55  15.0  4.5  310  21  − 54  92  73  − 102  2010 April 15  43.49  12.44  2.0  4.1  144  21  − 57  288  72  − 102  2010 June 16  38.83  16.14  15.0  4.1  109  50  − 38  225  62  − 133  2010 August 28  42.85  12.66  15.0  4.1  159  44  − 113  9  50  − 70  2010 September 17  41.49  15.63  30.1  4.3  148  45  − 25  256  73  − 132  2011 April 24  35.82  14.88  20.3  4.2  28  34  − 76  191  57  − 99  2011 May 24  43.86  12.03  5.0  4.2  266  52  − 132  142  54  − 49  2011 June 23  38.06  14.76  7.4  4.7  59  44  − 130  289  58  − 58  2011 July 06  38.01  14.80  7.5  4.1  115  44  − 53  249  56  − 120  2011 July 12  43.92  11.86  7.8  4.3  103  34  − 114  311  59  − 74  2011 July 12  43.92  11.85  7.4  4.2  109  37  − 102  304  54  − 81  2011 July 12  43.93  11.86  15.0  4.0  126  26  − 86  301  64  − 92  2011 July 25  44.98  7.28  25.1  4.7  264  28  − 60  50  66  − 105  2012 March 05  44.54  9.38  10.5  4.3  297  19  − 114  143  73  − 82  2012 March 15  42.81  13.20  6.0  4.0  297  36  − 99  128  54  − 83  2012 April 13  38.19  13.31  20.0  4.5  273  43  − 120  131  54  − 65  2012 May 28  39.86  16.12  3.0  4.5  137  31  − 119  350  63  − 74  2012 October 03  44.57  7.21  10.0  4.0  161  35  − 88  338  55  − 92  2012 October 25  39.88  16.01  15.0  5.3  162  40  − 84  334  50  − 95  2013 January 04  37.81  14.80  10.0  4.4  297  32  − 70  94  60  − 102  2013 February 16  41.71  13.58  11.0  4.9  309  47  − 118  168  50  − 63  2013 June 21  44.15  10.14  5.1  5.4  247  32  − 141  123  71  − 64  2013 June 21  44.16  10.15  10.0  4.3  325  49  − 54  97  52  − 124  2013 June 23  44.18  10.21  9.5  4.7  249  35  − 132  117  65  − 65  2013 June 30  44.17  10.20  9.8  4.8  281  21  − 91  102  69  − 90  2013 December 18  43.38  12.53  15.0  4.2  316  21  − 80  125  69  − 94  2013 December 22  43.38  12.52  10.0  4.3  158  22  − 54  301  73  − 103  2013 December 29  41.37  14.44  15.0  5.2  109  46  − 123  332  53  − 61  2014 January 20  41.36  14.45  11.0  4.4  137  29  − 65  289  64  − 103  2014 June 06  39.90  16.09  10.0  4.3  178  26  − 48  313  71  − 108  2014 April 07  44.47  6.69  5.0  4.9  29  40  − 68  181  54  − 107  2014 September 07  44.11  10.66  12.0  4.4  130  31  − 139  3  70  − 66  2014 December 28  39.29  16.36  11.0  4.5  14  40  − 84  186  50  − 95  2015 February 28  41.98  13.53  17.0  4.4  326  39  − 73  125  53  − 103  2015 August 03  39.16  16.53  26.0  4.2  255  49  − 46  20  57  − 128  Date  Lat (°)  Lon (°)  Depth (km)  Mw  Strike1 (°)  Dip1 (°)  Rake1 (°)  Strike2 (°)  Dip2 (°)  Rake2 (°)  1908 December 28  38.12  15.60  10.0  7.0  349  42  − 122  209  55  − 64  1915 January 13  41.99  13.65  8.0  6.9  135  63  − 90  315  26  − 89  1930 July 23  41.05  15.36  15.0  6.7  280  50  − 80  84  41  − 101  1939 February 11  44.07  11.65  7.0  4.7  310  49  − 120  171  49  − 60  1939 October 15  44.23  10.20  27.0  4.9  175  26  − 126  33  69  − 74  1941 March 16  38.44  12.12  20.0  6.9  217  39  − 76  19  52  − 101  1958 June 24  42.35  13.44  10.0  5.0  22  37  − 57  162  59  − 112  1962 August 21  41.13  14.95  8.0  5.7  310  65  − 130  201  54  − 31  1962 August 21  41.08  15.00  8.0  6.1  310  65  − 110  186  41  − 40  1967 December 09  42.00  16.50  33.0  4.7  277  74  − 90  97  15  − 89  1971 February 06  42.31  11.76  2.0  4.6  279  44  − 133  151  59  − 56  1971 February 12  43.23  12.49  33.0  4.5  290  48  − 139  169  60  − 50  1974 December 02  42.82  12.93  5.0  4.8  195  48  − 44  317  58  − 128  1977 June 05  37.88  14.46  10.0  4.6  61  26  − 139  293  73  − 70  1978 March 11  38.10  16.03  33.0  5.2  270  41  − 72  66  52  − 105  1978 July 30  42.65  12.46  10.0  4.4  209  42  − 55  345  57  − 117  1979 September 19  42.81  13.06  16.0  5.8  183  28  − 70  341  64  − 100  1980 February 20  39.30  16.21  12.0  4.3  14  43  − 78  178  48  − 101  1980 March 09  39.94  16.12  19.0  4.7  157  35  − 80  324  56  − 97  1980 May 14  40.46  15.85  24.0  4.8  119  38  − 112  326  56  − 74  1980 June 07  44.09  10.72  16.0  4.6  334  23  − 50  112  72  − 105  1980 June 09  42.29  13.88  20.0  4.7  266  37  − 88  84  53  − 91  1980 June 14  41.85  13.73  8.0  5.0  296  37  − 90  116  53  − 90  1980 November 23  40.91  15.37  10.0  6.9  135  41  − 80  303  50  − 98  1980 November 24  40.89  15.26  10.0  5.0  131  29  − 110  333  63  − 79  1980 November 25  40.70  15.47  10.0  4.9  129  26  − 65  281  67  − 102  1980 November 25  40.65  15.40  10.0  5.4  122  30  − 119  335  64  − 74  1981 January 16  40.95  15.37  15.0  5.2  115  30  − 93  298  60  − 89  1981 November 29  40.74  15.64  33.0  4.5  104  41  − 138  340  64  − 58  1982 March 21  39.70  15.64  18.9  5.2  15  39  − 127  239  60  − 64  1982 August 15  40.81  15.36  10.0  4.7  158  48  − 45  282  59  − 128  1982 October 17  43.12  12.59  13.0  4.6  132  39  − 125  354  59  − 65  1982 October 17  43.16  12.59  16.0  4.6  137  34  − 128  0  64  − 68  1982 October 18  43.13  12.63  19.0  4.6  143  27  − 131  8  70  − 71  1983 August 12  41.75  13.85  10.0  4.8  104  46  − 115  318  49  − 66  1984 April 22  43.62  10.19  15.0  4.6  349  38  − 67  141  56  − 107  1984 April 29  43.27  12.57  14.0  5.6  143  21  − 72  304  70  − 97  1984 May 07  41.77  13.89  10.0  5.9  174  31  − 52  312  66  − 110  1984 May 11  41.83  13.95  13.0  5.5  156  43  − 76  317  49  − 103  1986 October 01  44.34  10.19  28.0  4.5  135  43  − 91  316  47  − 90  1987 January 28  40.95  15.47  10.0  4.5  160  45  − 79  326  46  − 100  1987 July 05  43.78  12.23  11.0  4.5  298  43  − 83  108  48  − 97  1988 January 08  40.08  16.01  10.0  4.7  148  30  − 86  324  60  − 92  1993 June 05  43.12  12.68  8.0  4.6  139  37  − 108  341  55  − 77  1995 August 24  44.13  10.76  34.0  4.5  117  47  − 111  327  47  − 69  1996 April 03  40.76  15.49  10.0  4.9  123  30  − 110  325  62  − 79  1996 October 20  42.60  13.28  10.0  4.3  128  31  − 119  341  63  − 74  1996 December 14  37.81  13.84  40.0  4.3  123  23  − 43  254  74  − 108  1997 March 19  41.40  14.63  10.0  4.5  280  27  − 110  122  65  − 80  1997 September 03  43.01  12.90  10.2  4.5  137  30  − 88  315  60  − 91  1997 September 26  43.02  12.89  10.0  5.7  321  44  − 98  152  46  − 83  1997 September 26  43.03  12.85  10.0  6.0  144  42  − 80  312  49  − 98  1997 September 26  43.01  12.97  10.0  4.5  147  29  − 88  325  61  − 91  1997 September 26  43.06  12.85  10.0  4.3  193  45  − 43  316  61  − 126  1997 September 27  43.09  12.81  5.5  4.3  326  35  − 92  148  55  − 89  1997 September 27  43.02  12.83  10.0  4.2  288  36  − 135  160  66  − 63  1997 September 27  43.06  12.77  10.0  4.3  136  35  − 80  304  56  − 97  1997 October 02  43.64  12.14  10.0  4.4  158  41  − 58  298  56  − 115  1997 October 03  43.03  12.84  10.0  5.2  141  43  − 74  300  49  − 104  1997 October 04  42.90  12.90  10.0  4.4  299  42  − 101  133  49  − 81  1997 October 04  42.93  12.86  10.0  4.4  322  33  − 52  99  64  − 112  1997 October 04  42.94  12.93  10.0  4.7  318  42  − 80  125  49  − 99  1997 October 04  42.93  12.90  10.0  4.4  329  43  − 77  131  48  − 102  1997 October 06  43.02  12.84  10.0  5.4  145  40  − 80  312  51  − 98  1997 October 07  42.99  12.82  11.6  4.2  126  26  − 102  319  65  − 84  1997 October 07  43.03  12.85  10.0  4.5  141  42  − 77  304  49  − 101  1997 October 12  42.91  12.94  10.0  5.2  321  40  − 100  154  51  − 82  1997 October 12  42.86  12.97  10.0  4.3  271  14  − 133  136  80  − 80  1997 October 13  42.90  13.00  10.0  4.3  315  37  − 73  115  54  − 102  1997 October 13  42.89  12.92  10.0  4.4  305  35  − 96  133  56  − 86  1997 October 14  42.93  12.92  10.0  5.6  122  38  − 100  314  52  − 82  1997 October 15  42.93  12.89  10.0  4.4  329  40  − 65  117  55  − 110  1997 October 16  42.91  12.92  10.0  4.3  310  11  − 80  120  79  − 92  1997 October 16  42.98  12.89  10.0  4.1  118  35  − 88  295  55  − 92  1997 October 16  42.88  12.97  10.0  4.3  305  33  − 123  163  63  − 70  1997 October 17  42.89  12.91  10.0  4.2  326  48  − 53  97  54  − 124  1997 October 19  42.97  12.79  10.0  4.2  128  44  − 103  326  47  − 78  1997 October 25  42.84  13.01  10.0  4.3  333  33  − 54  112  64  − 111  1997 November 09  42.87  13.00  10.0  4.9  118  46  − 113  329  48  − 68  1997 November 30  42.88  12.95  10.0  4.3  125  36  − 119  339  59  − 70  1997 December 24  44.09  10.55  10.0  4.3  95  49  − 132  329  56  − 53  1997 December 31  42.87  12.99  10.0  4.3  293  35  − 135  164  66  − 64  1998 February 07  43.00  12.90  10.2  4.4  308  36  − 98  138  55  − 84  1998 March 21  42.90  12.90  10.0  5.0  137  15  − 97  325  75  − 88  1998 April 03  43.16  12.70  10.0  5.1  142  30  − 106  341  61  − 81  1998 April 03  43.23  12.67  10.0  4.3  152  33  − 108  352  59  − 79  1998 April 05  43.18  12.76  10.0  4.8  138  31  − 98  327  59  − 85  1998 June 02  43.17  12.73  10.0  4.3  311  42  − 124  173  56  − 63  1998 June 25  43.00  12.80  10.0  4.0  96  47  − 123  319  52  − 60  1998 August 15  42.41  12.98  10.0  4.4  298  26  − 52  76  70  − 107  1998 September 09  40.03  15.98  10.0  5.6  139  29  − 83  311  61  − 94  1999 February 14  38.17  15.06  33.0  4.7  18  39  − 108  220  53  − 76  1999 July 07  44.29  10.90  10.0  4.7  314  40  − 44  80  64  − 121  1999 October 10  42.67  13.19  10.0  4.2  348  50  − 47  112  55  − 129  1999 December 29  46.60  10.31  10.0  4.8  320  43  − 99  152  47  − 82  1999 December 31  46.60  10.32  10.0  4.1  13  34  − 45  143  67  − 116  2000 April 01  42.89  11.74  10.0  4.5  309  38  − 49  81  63  − 117  2000 April 06  46.60  10.33  5.0  4.0  359  47  − 64  144  49  − 115  2000 August 21  44.87  8.48  10.0  4.9  146  39  − 71  302  53  − 105  2000 October 03  44.27  10.80  10.0  4.2  317  24  − 105  153  67  − 83  2000 December 16  42.65  12.66  10.0  4.2  273  35  − 76  76  56  − 100  2001 October 18  39.10  16.61  10.0  4.3  332  44  − 88  149  46  − 92  2001 November 25  37.91  13.96  20.0  4.7  137  31  − 57  280  64  − 108  2001 November 26  43.60  12.10  10.0  4.7  358  21  − 72  158  70  − 97  2002 February 21  43.76  12.05  7.0  4.1  313  35  − 86  128  55  − 93  2002 April 18  40.69  15.58  10.0  4.5  329  13  − 72  131  77  − 94  2003 January 26  43.88  11.96  6.0  4.7  140  41  − 101  336  50  − 80  2003 January 26  43.88  11.95  7.0  4.5  291  37  − 130  158  62  − 64  2005 April 18  44.71  9.35  0.0  4.0  336  34  − 35  96  71  − 118  2006 February 27  38.15  15.20  9.0  4.4  22  24  − 95  208  66  − 88  2006 April 17  43.64  10.23  10.0  4.2  323  50  − 53  94  52  − 125  2006 December 19  37.78  14.91  23.0  4.2  18  16  − 40  147  80  − 102  2007 August 18  38.22  15.17  12.0  4.5  347  34  − 120  201  61  − 71  2007 October 21  42.38  12.97  10.0  4.2  330  31  − 44  100  69  − 113  2008 March 01  44.06  11.25  10.0  4.7  278  36  − 123  136  60  − 68  2008 March 01  44.35  11.49  10.0  4.0  318  32  − 108  160  60  − 79  2008 March 01  44.06  11.22  5.0  4.2  326  43  − 67  116  51  − 110  2008 April 08  39.16  16.66  10.0  4.4  235  49  − 35  350  64  − 134  2008 October 24  44.34  7.36  10.0  4.1  308  51  − 150  198  67  − 43  2009 March 30  42.33  13.36  11.0  4.4  2  35  − 70  158  57  − 104  2009 April 05  42.36  13.37  10.0  4.2  147  37  − 108  349  55  − 77  2009 April 06  42.33  13.33  10.0  6.3  326  35  − 80  134  56  − 97  2009 April 06  42.41  13.32  10.0  5.1  355  46  − 53  128  55  − 122  2009 April 06  42.38  13.34  10.0  4.5  340  25  − 103  175  66  − 84  2009 April 06  42.35  13.37  10.0  4.2  138  41  − 93  323  49  − 87  2009 April 06  42.36  13.33  10.0  4.4  348  40  − 64  135  55  − 111  2009 April 06  42.45  13.36  10.0  5.1  341  44  − 68  132  50  − 109  2009 April 07  42.34  13.39  10.0  5.1  341  41  − 64  128  54  − 111  2009 April 07  42.28  13.46  15.0  5.5  105  53  − 134  342  55  − 48  2009 April 07  42.38  13.38  10.0  4.5  321  41  − 64  108  54  − 110  2009 April 08  42.30  13.43  10.0  4.0  344  38  − 84  156  52  − 95  2009 April 08  42.51  13.36  10.0  4.1  319  40  − 76  121  51  − 101  2009 April 09  42.48  13.34  15.0  5.4  329  45  − 81  136  46  − 99  2009 April 09  42.50  13.36  17.0  5.2  321  44  − 83  132  46  − 97  2009 April 09  42.44  13.42  10.0  4.3  113  57  − 144  2  61  − 39  2009 April 13  42.50  13.36  10.0  5.0  337  38  − 71  133  54  − 104  2009 April 14  42.53  13.28  10.0  4.0  309  42  − 92  132  48  − 88  2009 April 15  42.54  13.28  10.0  4.1  113  33  − 126  333  64  − 69  2009 April 23  42.25  13.49  10.0  4.1  126  43  − 105  326  49  − 76  2009 April 23  42.23  13.48  10.0  4.3  323  27  − 95  149  63  − 87  2009 June 22  42.45  13.36  14.0  4.7  113  19  − 112  315  72  − 83  2009 July 03  42.41  13.39  10.0  4.1  144  42  − 108  348  50  − 74  2009 July 12  42.34  13.38  10.0  4.3  342  35  − 76  146  56  − 99  2009 September 24  42.45  13.33  10.0  4.2  184  35  − 76  347  56  − 100  2009 November 08  37.83  14.55  15.0  4.5  310  21  − 54  92  73  − 102  2010 April 15  43.49  12.44  2.0  4.1  144  21  − 57  288  72  − 102  2010 June 16  38.83  16.14  15.0  4.1  109  50  − 38  225  62  − 133  2010 August 28  42.85  12.66  15.0  4.1  159  44  − 113  9  50  − 70  2010 September 17  41.49  15.63  30.1  4.3  148  45  − 25  256  73  − 132  2011 April 24  35.82  14.88  20.3  4.2  28  34  − 76  191  57  − 99  2011 May 24  43.86  12.03  5.0  4.2  266  52  − 132  142  54  − 49  2011 June 23  38.06  14.76  7.4  4.7  59  44  − 130  289  58  − 58  2011 July 06  38.01  14.80  7.5  4.1  115  44  − 53  249  56  − 120  2011 July 12  43.92  11.86  7.8  4.3  103  34  − 114  311  59  − 74  2011 July 12  43.92  11.85  7.4  4.2  109  37  − 102  304  54  − 81  2011 July 12  43.93  11.86  15.0  4.0  126  26  − 86  301  64  − 92  2011 July 25  44.98  7.28  25.1  4.7  264  28  − 60  50  66  − 105  2012 March 05  44.54  9.38  10.5  4.3  297  19  − 114  143  73  − 82  2012 March 15  42.81  13.20  6.0  4.0  297  36  − 99  128  54  − 83  2012 April 13  38.19  13.31  20.0  4.5  273  43  − 120  131  54  − 65  2012 May 28  39.86  16.12  3.0  4.5  137  31  − 119  350  63  − 74  2012 October 03  44.57  7.21  10.0  4.0  161  35  − 88  338  55  − 92  2012 October 25  39.88  16.01  15.0  5.3  162  40  − 84  334  50  − 95  2013 January 04  37.81  14.80  10.0  4.4  297  32  − 70  94  60  − 102  2013 February 16  41.71  13.58  11.0  4.9  309  47  − 118  168  50  − 63  2013 June 21  44.15  10.14  5.1  5.4  247  32  − 141  123  71  − 64  2013 June 21  44.16  10.15  10.0  4.3  325  49  − 54  97  52  − 124  2013 June 23  44.18  10.21  9.5  4.7  249  35  − 132  117  65  − 65  2013 June 30  44.17  10.20  9.8  4.8  281  21  − 91  102  69  − 90  2013 December 18  43.38  12.53  15.0  4.2  316  21  − 80  125  69  − 94  2013 December 22  43.38  12.52  10.0  4.3  158  22  − 54  301  73  − 103  2013 December 29  41.37  14.44  15.0  5.2  109  46  − 123  332  53  − 61  2014 January 20  41.36  14.45  11.0  4.4  137  29  − 65  289  64  − 103  2014 June 06  39.90  16.09  10.0  4.3  178  26  − 48  313  71  − 108  2014 April 07  44.47  6.69  5.0  4.9  29  40  − 68  181  54  − 107  2014 September 07  44.11  10.66  12.0  4.4  130  31  − 139  3  70  − 66  2014 December 28  39.29  16.36  11.0  4.5  14  40  − 84  186  50  − 95  2015 February 28  41.98  13.53  17.0  4.4  326  39  − 73  125  53  − 103  2015 August 03  39.16  16.53  26.0  4.2  255  49  − 46  20  57  − 128  View Large Table 2. List of 128 earthquakes selected as input data and classified as thrust faulting focal mechanisms (TF, blue lower hemisphere focal mechanisms in Fig. 2). Date  Lat (°)  Lon (°)  Depth (km)  Mw  Strike1 (°)  Dip1 (°)  Rake1 (°)  Strike2 (°)  Dip2 (°)  Rake2 (°)  1967 December 30  44.63  12.01  33.0  5.2  322  56  84  152  34  98  1968 January 15  37.75  12.98  10.0  5.4  156  64  134  270  50  35  1976 May 06  46.36  13.27  11.7  6.4  282  23  119  71  70  78  1976 May 07  46.25  13.30  25.6  4.9  95  37  63  307  58  108  1976 May 09  46.26  13.36  19.7  5.1  89  48  60  310  50  119  1976 May 11  46.31  13.00  13.3  5.0  283  35  123  65  61  69  1976 September 11  46.33  13.20  9.6  5.3  271  38  116  60  56  71  1976 September 11  46.34  13.20  23.9  5.6  260  24  91  79  66  90  1976 September 15  46.32  13.20  1.9  5.9  246  36  84  73  54  94  1976 September 15  46.32  13.17  12.0  6.0  272  29  115  64  64  77  1977 September 16  46.33  13.00  12.0  5.2  291  35  119  77  60  72  1979 January 20  38.67  12.86  9.0  4.9  72  29  53  293  67  109  1979 December 08  38.28  11.74  33.0  5.3  235  45  67  87  50  111  1980 January 05  45.03  7.46  12.0  4.8  300  48  31  187  67  133  1980 May 28  38.48  14.25  14.0  5.7  83  43  99  252  48  82  1980 June 01  38.39  14.33  10.0  4.8  65  39  91  243  51  89  1981 February 14  41.05  14.60  10.0  4.9  254  46  157  1  73  46  1981 June 07  37.67  12.47  18.0  4.9  48  29  48  274  69  110  1981 June 22  38.49  14.09  13.0  4.8  71  47  116  215  49  65  1983 November 09  44.69  10.32  37.0  5.0  14  43  29  262  71  129  1986 January 08  42.59  15.31  27.0  4.7  312  43  95  125  47  86  1986 January 26  42.63  15.33  10.0  4.3  311  33  108  110  58  78  1986 August 29  46.34  12.47  10.0  4.7  219  47  62  77  50  117  1987 July 03  43.25  13.94  12.0  5.1  107  53  44  347  56  134  1988 April 26  42.37  16.57  24.0  5.4  289  44  121  68  53  63  1988 April 26  42.21  16.48  15.0  4.4  105  28  105  268  63  82  1990 February 01  42.20  15.57  10.0  4.4  227  29  66  74  64  103  1992 July 16  42.43  14.30  5.0  4.2  89  29  138  218  71  68  1995 September 30  41.90  15.97  10.0  5.2  197  32  58  53  64  108  1996 October 15  44.79  10.78  10.0  5.4  217  53  47  94  54  132  1996 October 15  44.78  10.73  10.0  4.4  275  45  139  36  63  53  1998 January 17  38.40  12.90  10.0  4.8  58  29  71  260  62  100  1998 May 06  46.24  13.71  10.0  4.3  247  44  40  127  64  127  1998 June 20  38.46  13.08  10.0  5.2  69  22  76  264  68  96  1998 June 21  38.50  13.10  10.0  4.6  69  36  77  265  55  99  1998 June 21  38.43  12.67  10.0  4.6  88  38  102  252  53  80  1998 September 14  38.46  13.60  10.0  5.0  72  30  80  263  60  96  1999 December 30  38.29  11.85  10.0  4.8  50  33  82  240  57  95  2000 April 26  40.98  10.10  10.0  4.8  179  39  83  8  51  96  2000 May 02  44.24  12.02  10.0  4.2  304  41  81  136  50  98  2000 May 06  44.14  11.97  10.0  4.1  287  33  64  137  61  106  2000 May 08  44.30  11.90  10.0  4.6  326  33  85  152  57  93  2000 May 09  44.20  12.00  10.0  4.3  308  31  96  121  59  87  2000 May 10  44.30  11.90  10.0  4.8  309  43  97  120  47  84  2000 May 11  44.34  11.91  10.0  4.2  303  46  117  86  50  64  2000 May 12  44.35  11.95  10.0  4.4  282  43  85  108  47  94  2000 June 27  40.95  10.03  10.0  4.3  184  27  82  13  64  94  2000 August 01  43.98  12.34  10.0  4.3  212  28  42  84  72  112  2000 September 02  43.26  12.99  33.0  4.4  325  40  82  156  51  97  2001 February 25  43.46  7.47  8.0  4.5  229  37  60  85  59  111  2001 May 26  37.46  16.34  33.0  4.5  71  54  134  192  55  46  2001 November 07  41.30  10.20  10.0  4.5  334  29  77  169  62  97  2002 April 05  38.48  14.74  10.0  4.4  90  41  108  246  52  75  2002 June 08  44.34  10.64  10.0  4.2  301  45  116  86  51  66  2002 June 18  44.44  10.80  33.0  4.3  293  44  103  95  48  78  2002 September 06  38.38  13.70  5.0  5.8  37  42  64  251  53  112  2002 September 06  38.44  13.73  4.0  4.7  252  48  126  24  53  56  2002 September 10  38.47  13.70  5.0  4.4  71  29  126  211  67  72  2002 September 20  38.46  13.74  5.0  4.7  46  33  77  241  58  99  2002 September 27  38.44  13.69  5.0  5.1  39  38  68  246  56  106  2002 September 28  38.47  13.71  5.0  4.6  79  39  103  243  52  80  2002 October 02  38.46  13.72  5.0  4.9  33  41  59  252  56  115  2002 October 23  42.61  17.16  16.0  4.3  103  43  69  311  50  108  2003 March 27  43.15  15.34  10.0  4.9  133  44  128  266  57  59  2003 March 29  43.11  15.46  10.0  5.5  287  41  85  114  49  95  2003 March 30  43.17  15.43  10.0  4.2  99  41  101  264  50  80  2003 March 30  43.17  15.53  10.0  4.6  98  43  83  287  47  96  2003 March 31  43.13  15.47  10.0  4.5  290  43  97  101  48  84  2003 April 03  43.15  15.43  10.0  4.3  105  25  116  256  67  78  2003 April 26  43.16  15.26  10.0  4.4  118  48  114  264  48  66  2003 April 29  43.25  15.57  10.0  4.4  109  32  61  322  63  107  2003 May 05  43.22  15.51  10.0  4.1  105  52  40  348  60  134  2003 June 21  43.07  15.31  10.0  4.4  249  40  62  103  56  111  2003 September 14  44.24  11.42  20.0  5.3  246  40  68  94  53  107  2003 December 07  44.16  12.18  9.0  4.2  284  45  71  130  48  108  2004 July 12  46.34  13.63  10.0  5.2  117  54  138  235  57  45  2004 November 24  45.63  10.56  17.0  5.0  235  25  92  53  65  89  2004 November 25  43.17  15.36  21.0  5.3  111  41  99  280  49  82  2004 December 03  43.09  15.50  10.0  4.6  279  32  91  97  58  89  2004 December 18  40.89  10.15  10.0  4.6  144  49  51  15  54  126  2006 April 16  44.02  11.81  10.0  4.5  295  34  91  114  56  89  2006 May 29  41.80  15.90  31.0  4.6  260  39  112  53  55  73  2006 June 22  39.73  16.60  15.0  4.7  173  44  100  339  47  80  2006 September 07  40.57  16.19  34.0  4.1  178  55  35  66  62  139  2006 December 10  41.94  16.20  35.0  4.5  28  31  83  217  59  94  2007 May 09  44.80  10.52  20.0  4.2  258  45  63  115  51  115  2008 February 21  37.82  17.97  30.0  4.7  333  27  134  106  71  71  2008 December 23  44.56  10.41  28.0  5.5  295  34  97  107  56  86  2008 December 23  44.52  10.39  31.0  4.9  286  34  84  113  57  94  2009 April 05  44.24  12.00  28.0  4.8  244  41  44  118  63  122  2009 September 07  38.59  14.04  10.0  4.8  276  41  124  54  57  64  2009 October 19  44.88  9.79  20.0  4.1  41  43  59  260  54  115  2010 June 04  42.37  16.59  15.0  4.3  61  48  62  279  49  117  2010 September 05  44.11  12.17  15.0  4.0  200  43  125  336  56  62  2011 July 07  42.06  7.60  10.0  5.1  43  39  93  219  51  87  2011 July 17  45.01  11.41  8.1  4.8  66  26  47  292  71  108  2011 October 20  44.53  9.41  10.0  4.2  278  34  62  131  60  108  2011 October 29  45.71  10.92  15.0  4.1  101  44  125  237  55  61  2012 March 04  42.03  7.63  2.0  4.5  35  33  84  222  57  94  2012 May 19  44.90  11.26  15.0  4.3  85  32  50  310  66  112  2012 May 20  44.89  11.25  10.0  6.1  109  30  99  279  60  85  2012 May 20  44.86  11.15  10.0  5.1  103  27  89  284  63  91  2012 May 20  44.83  11.49  15.0  5.2  100  37  64  312  57  109  2012 May 20  44.88  11.38  15.0  4.5  235  43  72  79  50  106  2012 May 21  44.85  11.35  15.0  4.1  243  37  92  60  53  89  2012 May 23  44.87  11.25  10.0  4.1  77  43  63  292  52  113  2012 May 29  44.85  11.09  15.0  6.0  110  20  103  276  71  85  2012 May 29  44.90  10.94  15.0  4.7  105  21  94  281  69  88  2012 May 29  44.89  11.01  6.8  5.5  112  32  101  279  59  83  2012 May 29  44.84  10.95  10.0  5.2  280  39  81  111  51  97  2012 June 03  44.90  10.94  15.0  4.9  92  16  37  326  81  103  2012 June 06  44.43  12.35  25.6  4.2  35  46  36  278  65  130  2012 June 09  46.21  12.44  7.1  4.2  240  31  88  62  59  91  2012 June 12  44.88  10.89  15.0  4.2  56  52  39  299  60  135  2012 August 13  38.52  13.73  26.5  4.2  19  24  63  229  69  102  2013 June 13  43.58  13.87  6.0  4.1  161  27  117  311  66  77  2013 July 21  43.53  13.74  10.0  5.2  109  41  56  331  57  116  2013 July 21  43.51  13.73  10.0  4.2  144  39  126  281  59  64  2013 August 22  43.58  13.69  10.0  4.5  144  30  93  321  60  89  2013 November 21  44.91  9.00  10.0  4.0  86  27  44  315  72  110  2013 December 15  36.67  14.94  15.0  4.1  83  47  143  200  63  49  2014 October 09  38.46  14.84  4.0  4.1  87  35  91  265  55  89  2014 August 28  45.67  10.70  10.0  4.0  72  45  123  209  54  61  2014 December 24  41.70  14.96  17.6  4.2  90  48  138  210  60  50  2015 May 29  42.92  14.30  10.0  4.5  338  41  108  135  51  75  2015 December 06  42.62  15.17  18.0  4.4  33  45  98  201  46  82  2015 December 06  42.45  15.30  5.0  4.6  229  34  120  15  61  72  2015 December 20  38.35  13.58  5.0  4.4  29  19  68  232  72  97  Date  Lat (°)  Lon (°)  Depth (km)  Mw  Strike1 (°)  Dip1 (°)  Rake1 (°)  Strike2 (°)  Dip2 (°)  Rake2 (°)  1967 December 30  44.63  12.01  33.0  5.2  322  56  84  152  34  98  1968 January 15  37.75  12.98  10.0  5.4  156  64  134  270  50  35  1976 May 06  46.36  13.27  11.7  6.4  282  23  119  71  70  78  1976 May 07  46.25  13.30  25.6  4.9  95  37  63  307  58  108  1976 May 09  46.26  13.36  19.7  5.1  89  48  60  310  50  119  1976 May 11  46.31  13.00  13.3  5.0  283  35  123  65  61  69  1976 September 11  46.33  13.20  9.6  5.3  271  38  116  60  56  71  1976 September 11  46.34  13.20  23.9  5.6  260  24  91  79  66  90  1976 September 15  46.32  13.20  1.9  5.9  246  36  84  73  54  94  1976 September 15  46.32  13.17  12.0  6.0  272  29  115  64  64  77  1977 September 16  46.33  13.00  12.0  5.2  291  35  119  77  60  72  1979 January 20  38.67  12.86  9.0  4.9  72  29  53  293  67  109  1979 December 08  38.28  11.74  33.0  5.3  235  45  67  87  50  111  1980 January 05  45.03  7.46  12.0  4.8  300  48  31  187  67  133  1980 May 28  38.48  14.25  14.0  5.7  83  43  99  252  48  82  1980 June 01  38.39  14.33  10.0  4.8  65  39  91  243  51  89  1981 February 14  41.05  14.60  10.0  4.9  254  46  157  1  73  46  1981 June 07  37.67  12.47  18.0  4.9  48  29  48  274  69  110  1981 June 22  38.49  14.09  13.0  4.8  71  47  116  215  49  65  1983 November 09  44.69  10.32  37.0  5.0  14  43  29  262  71  129  1986 January 08  42.59  15.31  27.0  4.7  312  43  95  125  47  86  1986 January 26  42.63  15.33  10.0  4.3  311  33  108  110  58  78  1986 August 29  46.34  12.47  10.0  4.7  219  47  62  77  50  117  1987 July 03  43.25  13.94  12.0  5.1  107  53  44  347  56  134  1988 April 26  42.37  16.57  24.0  5.4  289  44  121  68  53  63  1988 April 26  42.21  16.48  15.0  4.4  105  28  105  268  63  82  1990 February 01  42.20  15.57  10.0  4.4  227  29  66  74  64  103  1992 July 16  42.43  14.30  5.0  4.2  89  29  138  218  71  68  1995 September 30  41.90  15.97  10.0  5.2  197  32  58  53  64  108  1996 October 15  44.79  10.78  10.0  5.4  217  53  47  94  54  132  1996 October 15  44.78  10.73  10.0  4.4  275  45  139  36  63  53  1998 January 17  38.40  12.90  10.0  4.8  58  29  71  260  62  100  1998 May 06  46.24  13.71  10.0  4.3  247  44  40  127  64  127  1998 June 20  38.46  13.08  10.0  5.2  69  22  76  264  68  96  1998 June 21  38.50  13.10  10.0  4.6  69  36  77  265  55  99  1998 June 21  38.43  12.67  10.0  4.6  88  38  102  252  53  80  1998 September 14  38.46  13.60  10.0  5.0  72  30  80  263  60  96  1999 December 30  38.29  11.85  10.0  4.8  50  33  82  240  57  95  2000 April 26  40.98  10.10  10.0  4.8  179  39  83  8  51  96  2000 May 02  44.24  12.02  10.0  4.2  304  41  81  136  50  98  2000 May 06  44.14  11.97  10.0  4.1  287  33  64  137  61  106  2000 May 08  44.30  11.90  10.0  4.6  326  33  85  152  57  93  2000 May 09  44.20  12.00  10.0  4.3  308  31  96  121  59  87  2000 May 10  44.30  11.90  10.0  4.8  309  43  97  120  47  84  2000 May 11  44.34  11.91  10.0  4.2  303  46  117  86  50  64  2000 May 12  44.35  11.95  10.0  4.4  282  43  85  108  47  94  2000 June 27  40.95  10.03  10.0  4.3  184  27  82  13  64  94  2000 August 01  43.98  12.34  10.0  4.3  212  28  42  84  72  112  2000 September 02  43.26  12.99  33.0  4.4  325  40  82  156  51  97  2001 February 25  43.46  7.47  8.0  4.5  229  37  60  85  59  111  2001 May 26  37.46  16.34  33.0  4.5  71  54  134  192  55  46  2001 November 07  41.30  10.20  10.0  4.5  334  29  77  169  62  97  2002 April 05  38.48  14.74  10.0  4.4  90  41  108  246  52  75  2002 June 08  44.34  10.64  10.0  4.2  301  45  116  86  51  66  2002 June 18  44.44  10.80  33.0  4.3  293  44  103  95  48  78  2002 September 06  38.38  13.70  5.0  5.8  37  42  64  251  53  112  2002 September 06  38.44  13.73  4.0  4.7  252  48  126  24  53  56  2002 September 10  38.47  13.70  5.0  4.4  71  29  126  211  67  72  2002 September 20  38.46  13.74  5.0  4.7  46  33  77  241  58  99  2002 September 27  38.44  13.69  5.0  5.1  39  38  68  246  56  106  2002 September 28  38.47  13.71  5.0  4.6  79  39  103  243  52  80  2002 October 02  38.46  13.72  5.0  4.9  33  41  59  252  56  115  2002 October 23  42.61  17.16  16.0  4.3  103  43  69  311  50  108  2003 March 27  43.15  15.34  10.0  4.9  133  44  128  266  57  59  2003 March 29  43.11  15.46  10.0  5.5  287  41  85  114  49  95  2003 March 30  43.17  15.43  10.0  4.2  99  41  101  264  50  80  2003 March 30  43.17  15.53  10.0  4.6  98  43  83  287  47  96  2003 March 31  43.13  15.47  10.0  4.5  290  43  97  101  48  84  2003 April 03  43.15  15.43  10.0  4.3  105  25  116  256  67  78  2003 April 26  43.16  15.26  10.0  4.4  118  48  114  264  48  66  2003 April 29  43.25  15.57  10.0  4.4  109  32  61  322  63  107  2003 May 05  43.22  15.51  10.0  4.1  105  52  40  348  60  134  2003 June 21  43.07  15.31  10.0  4.4  249  40  62  103  56  111  2003 September 14  44.24  11.42  20.0  5.3  246  40  68  94  53  107  2003 December 07  44.16  12.18  9.0  4.2  284  45  71  130  48  108  2004 July 12  46.34  13.63  10.0  5.2  117  54  138  235  57  45  2004 November 24  45.63  10.56  17.0  5.0  235  25  92  53  65  89  2004 November 25  43.17  15.36  21.0  5.3  111  41  99  280  49  82  2004 December 03  43.09  15.50  10.0  4.6  279  32  91  97  58  89  2004 December 18  40.89  10.15  10.0  4.6  144  49  51  15  54  126  2006 April 16  44.02  11.81  10.0  4.5  295  34  91  114  56  89  2006 May 29  41.80  15.90  31.0  4.6  260  39  112  53  55  73  2006 June 22  39.73  16.60  15.0  4.7  173  44  100  339  47  80  2006 September 07  40.57  16.19  34.0  4.1  178  55  35  66  62  139  2006 December 10  41.94  16.20  35.0  4.5  28  31  83  217  59  94  2007 May 09  44.80  10.52  20.0  4.2  258  45  63  115  51  115  2008 February 21  37.82  17.97  30.0  4.7  333  27  134  106  71  71  2008 December 23  44.56  10.41  28.0  5.5  295  34  97  107  56  86  2008 December 23  44.52  10.39  31.0  4.9  286  34  84  113  57  94  2009 April 05  44.24  12.00  28.0  4.8  244  41  44  118  63  122  2009 September 07  38.59  14.04  10.0  4.8  276  41  124  54  57  64  2009 October 19  44.88  9.79  20.0  4.1  41  43  59  260  54  115  2010 June 04  42.37  16.59  15.0  4.3  61  48  62  279  49  117  2010 September 05  44.11  12.17  15.0  4.0  200  43  125  336  56  62  2011 July 07  42.06  7.60  10.0  5.1  43  39  93  219  51  87  2011 July 17  45.01  11.41  8.1  4.8  66  26  47  292  71  108  2011 October 20  44.53  9.41  10.0  4.2  278  34  62  131  60  108  2011 October 29  45.71  10.92  15.0  4.1  101  44  125  237  55  61  2012 March 04  42.03  7.63  2.0  4.5  35  33  84  222  57  94  2012 May 19  44.90  11.26  15.0  4.3  85  32  50  310  66  112  2012 May 20  44.89  11.25  10.0  6.1  109  30  99  279  60  85  2012 May 20  44.86  11.15  10.0  5.1  103  27  89  284  63  91  2012 May 20  44.83  11.49  15.0  5.2  100  37  64  312  57  109  2012 May 20  44.88  11.38  15.0  4.5  235  43  72  79  50  106  2012 May 21  44.85  11.35  15.0  4.1  243  37  92  60  53  89  2012 May 23  44.87  11.25  10.0  4.1  77  43  63  292  52  113  2012 May 29  44.85  11.09  15.0  6.0  110  20  103  276  71  85  2012 May 29  44.90  10.94  15.0  4.7  105  21  94  281  69  88  2012 May 29  44.89  11.01  6.8  5.5  112  32  101  279  59  83  2012 May 29  44.84  10.95  10.0  5.2  280  39  81  111  51  97  2012 June 03  44.90  10.94  15.0  4.9  92  16  37  326  81  103  2012 June 06  44.43  12.35  25.6  4.2  35  46  36  278  65  130  2012 June 09  46.21  12.44  7.1  4.2  240  31  88  62  59  91  2012 June 12  44.88  10.89  15.0  4.2  56  52  39  299  60  135  2012 August 13  38.52  13.73  26.5  4.2  19  24  63  229  69  102  2013 June 13  43.58  13.87  6.0  4.1  161  27  117  311  66  77  2013 July 21  43.53  13.74  10.0  5.2  109  41  56  331  57  116  2013 July 21  43.51  13.73  10.0  4.2  144  39  126  281  59  64  2013 August 22  43.58  13.69  10.0  4.5  144  30  93  321  60  89  2013 November 21  44.91  9.00  10.0  4.0  86  27  44  315  72  110  2013 December 15  36.67  14.94  15.0  4.1  83  47  143  200  63  49  2014 October 09  38.46  14.84  4.0  4.1  87  35  91  265  55  89  2014 August 28  45.67  10.70  10.0  4.0  72  45  123  209  54  61  2014 December 24  41.70  14.96  17.6  4.2  90  48  138  210  60  50  2015 May 29  42.92  14.30  10.0  4.5  338  41  108  135  51  75  2015 December 06  42.62  15.17  18.0  4.4  33  45  98  201  46  82  2015 December 06  42.45  15.30  5.0  4.6  229  34  120  15  61  72  2015 December 20  38.35  13.58  5.0  4.4  29  19  68  232  72  97  View Large Table 3. List of 85 earthquakes selected as input data and classified as strike-slip faulting focal mechanisms (SS, green lower hemisphere focal mechanisms in Fig. 2). Date  Lat (°)  Lon (°)  Depth (km)  Mw  Strike1 (°)  Dip1 (°)  Rake1 (°)  Strike2 (°)  Dip2 (°)  Rake2 (°)  1951 May 15  45.33  9.33  6.0  5.0  235  73  − 171  142  81  − 17  1951 May 16  45.33  9.33  6.0  4.5  123  64  − 17  220  74  − 152  1967 October 31  37.84  14.60  38.0  5.0  9  62  − 169  273  80  − 28  1970 August 19  43.25  10.77  33.0  4.7  35  57  − 156  291  70  − 35  1971 May 06  41.20  15.24  33.0  4.8  252  85  174  161  85  5  1971 November 29  40.34  15.77  4.0  4.7  23  84  6  292  84  173  1975 June 19  41.65  15.73  18.0  4.9  281  71  168  14  78  19  1975 November 16  44.75  9.52  20.0  4.8  312  62  − 32  58  62  − 147  1978 April 15  38.39  15.07  14.0  6.0  135  60  − 176  43  86  − 30  1979 April 18  46.36  13.28  10.0  4.7  323  66  169  58  80  24  1980 December 23  44.71  9.94  10.0  4.6  35  61  − 20  135  72  − 149  1981 February 14  41.05  14.60  10.0  4.9  254  46  157  1  73  46  1987 May 02  44.82  10.72  10.0  4.7  45  73  8  312  83  163  1989 September 13  45.80  11.21  10.0  4.9  56  89  0  146  90  − 179  1989 December 22  43.06  12.76  33.0  4.6  185  47  12  87  81  136  1990 May 05  40.75  15.85  26.0  5.8  184  73  13  90  78  162  1990 May 05  40.75  15.81  15.0  4.8  282  83  173  13  83  7  1990 October 29  36.23  14.67  23.0  4.8  198  72  − 13  292  78  − 161  1990 December 13  37.32  15.25  10.0  5.6  274  64  174  7  85  26  1991 February 11  44.87  6.70  14.0  4.5  224  76  − 11  316  79  − 166  1991 May 26  40.73  15.77  8.0  5.1  183  71  − 9  276  81  − 160  1993 June 26  37.92  14.21  10.0  4.8  170  53  6  76  85  143  1995 May 29  37.90  12.07  11.0  4.8  82  70  − 180  351  90  − 20  1995 October 10  44.18  10.01  10.0  4.8  89  68  178  180  88  22  1995 December 31  44.47  10.65  27.0  4.0  144  70  − 174  52  84  − 20  1997 March 25  36.93  16.03  33.0  4.5  104  78  179  194  89  12  1997 October 16  43.04  12.89  10.0  4.3  287  80  175  18  85  10  1998 April 12  46.24  13.65  10.0  5.6  218  67  − 4  309  87  − 157  1999 January 25  44.02  11.92  33.0  4.4  91  66  17  354  75  155  2000 June 18  44.76  10.73  5.0  4.4  308  68  − 161  210  73  − 23  2001 April 22  37.72  15.10  10.0  4.2  316  56  27  210  68  143  2001 July 17  46.70  11.30  10.0  4.8  210  72  7  117  83  162  2001 July 18  44.84  8.40  10.0  4.1  95  49  179  185  89  41  2002 October 27  37.79  15.16  10.0  4.9  320  60  171  55  82  30  2002 October 27  37.92  15.18  10.0  4.5  67  54  19  326  75  142  2002 October 29  37.67  15.27  10.0  4.7  316  61  − 173  223  84  − 29  2002 October 29  37.69  15.56  10.0  4.2  207  54  − 28  314  68  − 141  2002 October 31  41.79  14.87  10.0  5.7  174  67  − 8  267  82  − 157  2002 November 01  41.73  14.88  10.0  5.7  170  75  − 4  261  86  − 165  2002 November 01  41.87  14.83  10.0  4.5  263  56  − 166  165  78  − 35  2002 November 12  41.66  14.77  10.0  4.6  72  80  171  163  82  10  2003 April 11  44.79  8.89  4.0  4.8  297  75  − 165  203  75  − 16  2003 June 01  41.66  14.82  12.0  4.5  167  72  − 12  261  79  − 162  2003 July 07  36.01  14.90  10.0  4.3  350  62  4  258  87  152  2003 December 30  41.64  14.85  5.0  4.5  187  53  − 6  281  85  − 142  2005 August 22  41.47  12.53  10.0  4.8  341  62  180  71  90  28  2005 September 08  46.00  6.90  7.0  4.5  317  61  − 15  54  77  − 151  2006 April 10  43.40  13.49  33.0  4.1  89  71  − 169  355  80  − 20  2006 April 17  39.57  17.14  10.0  4.7  223  83  177  314  87  7  2006 October 04  42.07  15.75  36.0  4.3  274  79  178  4  89  11  2006 October 21  43.65  13.00  36.0  4.2  34  60  12  298  80  150  2006 November 23  35.97  12.94  10.0  4.8  357  70  − 2  88  88  − 160  2006 November 24  36.26  15.76  11.0  4.4  188  82  0  98  90  172  2008 March 19  41.91  15.85  28.0  4.2  69  57  145  179  61  38  2008 November 20  39.14  17.49  15.0  4.5  166  82  − 2  256  88  − 172  2008 November 28  37.54  13.69  35.0  4.4  337  74  9  245  81  164  2009 March 19  36.52  12.72  28.0  4.4  255  48  − 180  165  90  − 42  2009 April 09  42.34  13.44  18.0  4.4  67  50  − 170  331  83  − 40  2009 September 20  43.40  13.39  37.0  4.7  21  78  − 3  112  87  − 168  2009 December 15  43.01  12.28  15.0  4.2  163  75  2  72  88  165  2009 December 19  37.78  14.94  15.0  4.3  119  47  − 178  28  89  − 43  2010 January 12  43.26  13.47  31.0  4.1  52  48  − 161  309  76  − 44  2010 April 02  37.76  15.11  2.0  4.2  274  55  10  178  82  145  2010 August 16  38.36  14.95  10.0  4.7  221  73  − 6  312  85  − 163  2010 October 13  44.14  12.37  35.2  4.1  17  65  22  278  70  153  2010 October 15  38.87  16.66  15.0  4.4  287  62  173  20  84  28  2011 May 06  37.78  14.96  22.2  4.3  13  57  15  275  77  146  2011 November 15  38.26  14.67  15.0  4.2  7  63  − 6  99  85  − 152  2012 January 24  45.54  10.97  15.0  4.1  107  66  − 170  13  81  − 24  2012 Januray 25  44.85  10.54  33.0  5.0  335  46  − 16  76  79  − 135  2012 July 04  37.69  16.87  40.0  4.6  186  74  3  95  87  164  2012 August 12  41.77  16.27  8.4  4.1  267  55  149  16  65  39  2012 October 03  44.85  9.77  30.0  4.5  216  85  − 2  306  88  − 175  2012 November 22  37.80  14.96  10.0  4.1  258  65  154  359  66  28  2012 November 22  37.77  14.99  20.0  4.2  6  57  23  263  71  145  2013 January 25  44.17  10.45  15.0  5.0  246  68  − 167  151  78  − 22  2013 March 24  37.76  16.50  30.0  4.6  257  87  178  347  88  3  2014 January 14  38.37  14.92  12.0  4.1  315  78  171  46  81  12  2014 January 14  38.36  14.94  11.0  4.2  308  47  159  52  75  45  2014 December 19  43.61  11.26  10.0  4.3  257  50  − 166  157  79  − 40  2014 September 26  36.78  16.50  40.0  4.2  267  75  170  359  80  16  2014 December 19  43.60  11.25  10.0  4.2  345  78  − 9  76  81  − 168  2015 April 16  41.79  15.34  22.5  4.1  4  73  12  271  78  163  2015 August 08  38.55  14.26  14.0  4.0  350  77  4  259  86  167  2015 August 29  46.31  13.58  10.0  4.0  139  55  147  249  64  40  Date  Lat (°)  Lon (°)  Depth (km)  Mw  Strike1 (°)  Dip1 (°)  Rake1 (°)  Strike2 (°)  Dip2 (°)  Rake2 (°)  1951 May 15  45.33  9.33  6.0  5.0  235  73  − 171  142  81  − 17  1951 May 16  45.33  9.33  6.0  4.5  123  64  − 17  220  74  − 152  1967 October 31  37.84  14.60  38.0  5.0  9  62  − 169  273  80  − 28  1970 August 19  43.25  10.77  33.0  4.7  35  57  − 156  291  70  − 35  1971 May 06  41.20  15.24  33.0  4.8  252  85  174  161  85  5  1971 November 29  40.34  15.77  4.0  4.7  23  84  6  292  84  173  1975 June 19  41.65  15.73  18.0  4.9  281  71  168  14  78  19  1975 November 16  44.75  9.52  20.0  4.8  312  62  − 32  58  62  − 147  1978 April 15  38.39  15.07  14.0  6.0  135  60  − 176  43  86  − 30  1979 April 18  46.36  13.28  10.0  4.7  323  66  169  58  80  24  1980 December 23  44.71  9.94  10.0  4.6  35  61  − 20  135  72  − 149  1981 February 14  41.05  14.60  10.0  4.9  254  46  157  1  73  46  1987 May 02  44.82  10.72  10.0  4.7  45  73  8  312  83  163  1989 September 13  45.80  11.21  10.0  4.9  56  89  0  146  90  − 179  1989 December 22  43.06  12.76  33.0  4.6  185  47  12  87  81  136  1990 May 05  40.75  15.85  26.0  5.8  184  73  13  90  78  162  1990 May 05  40.75  15.81  15.0  4.8  282  83  173  13  83  7  1990 October 29  36.23  14.67  23.0  4.8  198  72  − 13  292  78  − 161  1990 December 13  37.32  15.25  10.0  5.6  274  64  174  7  85  26  1991 February 11  44.87  6.70  14.0  4.5  224  76  − 11  316  79  − 166  1991 May 26  40.73  15.77  8.0  5.1  183  71  − 9  276  81  − 160  1993 June 26  37.92  14.21  10.0  4.8  170  53  6  76  85  143  1995 May 29  37.90  12.07  11.0  4.8  82  70  − 180  351  90  − 20  1995 October 10  44.18  10.01  10.0  4.8  89  68  178  180  88  22  1995 December 31  44.47  10.65  27.0  4.0  144  70  − 174  52  84  − 20  1997 March 25  36.93  16.03  33.0  4.5  104  78  179  194  89  12  1997 October 16  43.04  12.89  10.0  4.3  287  80  175  18  85  10  1998 April 12  46.24  13.65  10.0  5.6  218  67  − 4  309  87  − 157  1999 January 25  44.02  11.92  33.0  4.4  91  66  17  354  75  155  2000 June 18  44.76  10.73  5.0  4.4  308  68  − 161  210  73  − 23  2001 April 22  37.72  15.10  10.0  4.2  316  56  27  210  68  143  2001 July 17  46.70  11.30  10.0  4.8  210  72  7  117  83  162  2001 July 18  44.84  8.40  10.0  4.1  95  49  179  185  89  41  2002 October 27  37.79  15.16  10.0  4.9  320  60  171  55  82  30  2002 October 27  37.92  15.18  10.0  4.5  67  54  19  326  75  142  2002 October 29  37.67  15.27  10.0  4.7  316  61  − 173  223  84  − 29  2002 October 29  37.69  15.56  10.0  4.2  207  54  − 28  314  68  − 141  2002 October 31  41.79  14.87  10.0  5.7  174  67  − 8  267  82  − 157  2002 November 01  41.73  14.88  10.0  5.7  170  75  − 4  261  86  − 165  2002 November 01  41.87  14.83  10.0  4.5  263  56  − 166  165  78  − 35  2002 November 12  41.66  14.77  10.0  4.6  72  80  171  163  82  10  2003 April 11  44.79  8.89  4.0  4.8  297  75  − 165  203  75  − 16  2003 June 01  41.66  14.82  12.0  4.5  167  72  − 12  261  79  − 162  2003 July 07  36.01  14.90  10.0  4.3  350  62  4  258  87  152  2003 December 30  41.64  14.85  5.0  4.5  187  53  − 6  281  85  − 142  2005 August 22  41.47  12.53  10.0  4.8  341  62  180  71  90  28  2005 September 08  46.00  6.90  7.0  4.5  317  61  − 15  54  77  − 151  2006 April 10  43.40  13.49  33.0  4.1  89  71  − 169  355  80  − 20  2006 April 17  39.57  17.14  10.0  4.7  223  83  177  314  87  7  2006 October 04  42.07  15.75  36.0  4.3  274  79  178  4  89  11  2006 October 21  43.65  13.00  36.0  4.2  34  60  12  298  80  150  2006 November 23  35.97  12.94  10.0  4.8  357  70  − 2  88  88  − 160  2006 November 24  36.26  15.76  11.0  4.4  188  82  0  98  90  172  2008 March 19  41.91  15.85  28.0  4.2  69  57  145  179  61  38  2008 November 20  39.14  17.49  15.0  4.5  166  82  − 2  256  88  − 172  2008 November 28  37.54  13.69  35.0  4.4  337  74  9  245  81  164  2009 March 19  36.52  12.72  28.0  4.4  255  48  − 180  165  90  − 42  2009 April 09  42.34  13.44  18.0  4.4  67  50  − 170  331  83  − 40  2009 September 20  43.40  13.39  37.0  4.7  21  78  − 3  112  87  − 168  2009 December 15  43.01  12.28  15.0  4.2  163  75  2  72  88  165  2009 December 19  37.78  14.94  15.0  4.3  119  47  − 178  28  89  − 43  2010 January 12  43.26  13.47  31.0  4.1  52  48  − 161  309  76  − 44  2010 April 02  37.76  15.11  2.0  4.2  274  55  10  178  82  145  2010 August 16  38.36  14.95  10.0  4.7  221  73  − 6  312  85  − 163  2010 October 13  44.14  12.37  35.2  4.1  17  65  22  278  70  153  2010 October 15  38.87  16.66  15.0  4.4  287  62  173  20  84  28  2011 May 06  37.78  14.96  22.2  4.3  13  57  15  275  77  146  2011 November 15  38.26  14.67  15.0  4.2  7  63  − 6  99  85  − 152  2012 January 24  45.54  10.97  15.0  4.1  107  66  − 170  13  81  − 24  2012 Januray 25  44.85  10.54  33.0  5.0  335  46  − 16  76  79  − 135  2012 July 04  37.69  16.87  40.0  4.6  186  74  3  95  87  164  2012 August 12  41.77  16.27  8.4  4.1  267  55  149  16  65  39  2012 October 03  44.85  9.77  30.0  4.5  216  85  − 2  306  88  − 175  2012 November 22  37.80  14.96  10.0  4.1  258  65  154  359  66  28  2012 November 22  37.77  14.99  20.0  4.2  6  57  23  263  71  145  2013 January 25  44.17  10.45  15.0  5.0  246  68  − 167  151  78  − 22  2013 March 24  37.76  16.50  30.0  4.6  257  87  178  347  88  3  2014 January 14  38.37  14.92  12.0  4.1  315  78  171  46  81  12  2014 January 14  38.36  14.94  11.0  4.2  308  47  159  52  75  45  2014 December 19  43.61  11.26  10.0  4.3  257  50  − 166  157  79  − 40  2014 September 26  36.78  16.50  40.0  4.2  267  75  170  359  80  16  2014 December 19  43.60  11.25  10.0  4.2  345  78  − 9  76  81  − 168  2015 April 16  41.79  15.34  22.5  4.1  4  73  12  271  78  163  2015 August 08  38.55  14.26  14.0  4.0  350  77  4  259  86  167  2015 August 29  46.31  13.58  10.0  4.0  139  55  147  249  64  40  View Large 3.2 Testing data The independent data set used to evaluate the reliability of the results consists of a set of earthquake focal mechanism solutions (http://cnt.rm.ingv.it/tdmt—2017 March 9) occurred within the Italian gridding zone (Fig. 1) during the year 2016 and characterized by the same boundary parameters of the input-data earthquakes, as magnitude ≥ 4 (except for only one Mw 3.9 earthquake) and hypocentral depth less than 40 km. We consider nine out-of-sample earthquakes (Fig. 1 and Table 4): Reggio Emilia (inner northern Apennine, Mw 4.0 December 9), Terni (central Apennine, Mw 4.1 May 30), Amatrice (central Apennine, Mw 6.0 August 24, Mw 5.9 October 26 and Mw 6.5 October 30), Firenze (Tuscany, Mw 3.9 October 25), Campobasso (Molise, Mw 4.3 January 16), Siracusa (Sicily, Mw 4.2 February 8) and Ionio (Ionian-Sea, Mw 4.0 March 6). Table 4. List of nine earthquakes focal mechanism s parameters (http://cnt.rm.ingv.it/) used as testing data shown in Fig. 1 (location) and Fig. 7 (black and white lower hemisphere focal mechanisms). Date  Location  Lat (°)  Lon (°)  Depth (km)  Mw  Strike1 (°)  Dip1 (°)  Rake1 (°)  Strike2 (°)  Dip2 (°)  Rake2 (°)  2016 January 16  e  41.5337  14.5995  6  4.3  305  49  102  143  43  77  2016 February 08  f  36.9765  14.8692  6  4.2  282  83  170  191  80  7  2016 March 06  g  38.1838  16.7505  39  4.0  248  75  158  344  69  16  2016 May 30  b  42.7115  11.9648  5  4.1  124  47  − 87  300  43  − 93  2016 August 24  c  42.7063  13.2232  5  6.0  155  49  − 87  331  41  − 93  2016 October 25  d  43.6007  10.994  9  3.9  260  89  158  350  68  1  2016 October 26  c  42.9152  13.1278  6  5.9  159  47  − 93  344  43  − 87  2016 October 30  c  42.8398  13.1102  5  6.5  151  47  − 89  330  43  − 91  2016 December 09  a  44.3298  10.5002  6  4.0  162  53  − 82  329  38  − 100  Date  Location  Lat (°)  Lon (°)  Depth (km)  Mw  Strike1 (°)  Dip1 (°)  Rake1 (°)  Strike2 (°)  Dip2 (°)  Rake2 (°)  2016 January 16  e  41.5337  14.5995  6  4.3  305  49  102  143  43  77  2016 February 08  f  36.9765  14.8692  6  4.2  282  83  170  191  80  7  2016 March 06  g  38.1838  16.7505  39  4.0  248  75  158  344  69  16  2016 May 30  b  42.7115  11.9648  5  4.1  124  47  − 87  300  43  − 93  2016 August 24  c  42.7063  13.2232  5  6.0  155  49  − 87  331  41  − 93  2016 October 25  d  43.6007  10.994  9  3.9  260  89  158  350  68  1  2016 October 26  c  42.9152  13.1278  6  5.9  159  47  − 93  344  43  − 87  2016 October 30  c  42.8398  13.1102  5  6.5  151  47  − 89  330  43  − 91  2016 December 09  a  44.3298  10.5002  6  4.0  162  53  − 82  329  38  − 100  View Large 3.3 The forecasting model Here, we describe the model that is used to forecast the focal mechanism and faulting style of the next moderate to large earthquakes in the Italian region. The model assumes that the stress field in Italy of the next decades will be the same of the past decades; hence, we combine the focal mechanism of the past seismicity to obtain an ‘average’ moment tensor for the next earthquakes. The methodology is inspired by the Cumulative Moment Tensor technique proposed by Kostrov (1974) and subsequently exploited by Selva & Marzocchi (2004). The Cumulative Moment Tensor describes the contribution of each earthquake to the average strain tensor ε within a rock volume V. This strain is proportional to the moment tensor $${{\cal M}_{ij}}$$, so that the average strain induced by earthquakes is given by   \begin{equation}{\varepsilon _{ij}} = \ \frac{1}{{2\mu V}}\mathop \sum \limits_{k = 1}^N {\cal M}_{ij}^{( {\boldsymbol{k}})}\end{equation} (1)where μ is the shear modulus, and the sum is taken for the N earthquakes located within the volume. Eq. (1) represents a basic equation of moment tensor summation method that defines seismic deformation for a defined small area. Selva & Marzocchi (2004) generalize the same concept introducing the Weighted Cumulative Moment Tensor (WCMT) that takes into account the distance of the information from a specific point, for instance, the centre of the cell of a grid. In this case, the cumulative seismic moment tensor for a generic kth cell is   \begin{equation} \widetilde {{{\cal M}_k}} = \ \frac{{\mathop \sum \nolimits_{l = 1}^{{N_k}} {{\cal M}_l} \cdot {\omega _{lk}}}}{{\mathop \sum \nolimits_{l = 1}^{{N_k}} {\omega _{lk}}}}\end{equation} (2)where $$\widetilde {{{\cal M}_k}}$$ is the average seismic moment tensor of the kth cell, $${{\cal M}_l}$$ is the seismic moment tensor of the lth earthquake at a distance Δlk from the centre of the kth cell and ωlk is   \begin{equation}{\omega _{lk}} = \ \frac{1}{{{\rm{\Delta }}_{lk}^2}}\end{equation} (3)Eq. (3) is applied only for a maximum distance R = 50 km. This threshold accounts for the geological and geodynamic complexity of Italy and the highly heterogeneous spatial distribution of the considered stress data. Previous papers on stress interpolation analysis (Pierdominici & Heidbach 2012; Carafa & Barba 2013) investigated extensively the problem to define a meaningful search radius in Italy, finding comparable R-values. From a practical point of view, by using this threshold, we exclude data too distant to be considered representative for the kth cell. Adopting the WCMT concept, we estimate the seismic moment tensor parameters for each one of 8993 cells (0.1° × 0.1° spaced) in which we have equally divided the study area (Fig. 2). In particular, we apply eq. (2) to calculate the average moment tensor for each possible faulting style α = {NF, TF, SS} where NF, TF and SS mean normal, reverse and strike-slip faulting, respectively. In other words, we average only the same faulting style information defining the Total Weighted Moment Tensor ($${\rm{TWMT}}_k^{( \alpha )}$$)   \begin{equation}{\rm{TWMT}}_k^{(\alpha)} = \widetilde{{\cal M}}_k^{( \alpha)} = \ \frac{{\mathop \sum \nolimits_{l = 1}^{N_k^{(\alpha)}} {\cal M}_l^{(\alpha)} \cdot {\omega _{lk}}}}{{\mathop \sum \nolimits_{l = 1}^{N_k^{(\alpha)}} {\omega _{lk}}}}\end{equation} (4)where $$N_k^{( \alpha )}$$ is the number of past earthquakes at a distance Δlk ≤ R from the kth each. The eigenvalues and eigenvectors of the tensor $${\rm{TWMT}}_k^{( \alpha )}$$ are the average $$T_k^{( \alpha )},\ P_k^{( \alpha )},\ B_k^{( \alpha )}$$, that is, they are the average orientations of T, P and B axes in the kth cell. Then, applying the Zoback (1992) criteria, we obtain the weighted azimuths of SHmax for each kth cell. The last step of the procedure is to compute the conditional probability of mechanism α given an earthquake is occurred in the kth cell. For this purpose, we define   \begin{equation}C_k^{(\alpha)} = \ \mathop \sum \limits_{l = 1}^{N_k^{(\alpha)}} {\omega _{lk}}\end{equation} (5)that provides the overall weight of the information related to the faulting type α. Hence, the conditional probability of the next focal mechanism α in the kth cell given the occurrence of an earthquake can be estimated by   \begin{equation}P_k^{(\alpha)} = \ \frac{{C_k^{(\alpha)}}}{{C_k^{\left( {{\rm{TOT}}} \right)}}}\end{equation} (6)where   \begin{equation}C_k^{\left( {{\rm{TOT}}} \right)} = \ C_k^{\left( {{\rm{NF}}} \right)} + C_k^{\left( {{\rm{TF}}} \right)} + C_k^{\left( {{\rm{SS}}} \right)}\end{equation} (7) The use of eq. (6) to estimate the conditional probability of the focal mechanism α in the kth cell requires some further discussion. This definition of probability satisfies the Kolmogorov axioms (Kolmogorov 1956) and it can be interpreted in the Bayesian perspective of bet quotient or degree of belief (e.g. Lindley 2000). Assuming that only one specific (unknown) focal mechanism is allowed in each cell of the grid for earthquakes of interest in PSHA, the probability of eq. (6) does not describe the expected frequency of focal mechanisms that are going to be observed in the cell, but it describes only the epistemic uncertainty through the subjective concept of bet quotient. For practical purpose, the user may consider all possibilities (to fully consider the epistemic uncertainty) or just take the most likely outcome. We also assign a sort of degree of accuracy of the results taking into account the value of $$C_k^{( {{\rm{TOT}}} )}$$ in eq. (7); de facto, this quantity gives a measure of how many earthquakes and their proximity to the cell have been considered to estimate the focal mechanisms. We define three classes based on the total contribution of weights in the cell of interest (eq. 7): (i) if $$C_k^{( {{\rm{TOT}}} )}$$ ≤ 33th percentile of the distribution of $$C_k^{( {{\rm{TOT}}} )}$$ for all cells, the kth cell belongs to ‘Class 1’; (ii) if $$C_k^{( {{\rm{TOT}}} )}$$ is comprised between 33th and 66th percentile the cell belongs to ‘Class 2’ and (iii) if $$C_k^{( {{\rm{TOT}}} )}$$ ≥ 66th percentile the cell belongs to ‘Class 3’. As final consideration, we remark that using eq. (6) we may get probability equal to 1 in some cell. Although here we do not deepen this problem, we strongly encourage practitioners to avoid using probabilities equal to 1. This can be easily done introducing a 'surprise' factor ε   \begin{equation}\widetilde {P_k^{(\alpha)}} = \ P_k^{(\alpha)} - \epsilon \end{equation} (8)and using $$\widetilde {P_k^{( \alpha )}}$$ instead of $$P_k^{( \alpha )}$$. The surprise factor is the probability that the next earthquake may have an unexpected focal mechanism; hence it may depend on the class of accuracy defined above. 4 RESULTS We compute separately the TWMT for each possible faulting style according to eq. (4). In Table S1–S3 (Supporting Information), we show all expected moment tensors and the probability of occurrence associated to different faulting styles, for each cell of the grid. In Fig. 3, we show the spatial distribution of the prevailing focal mechanisms represented by lower hemisphere focal mechanisms (NF in red, TF in blue and SS in green). The map shows all tectonic regimes with prevailing NF along the entire Apennines, reverse faulting along the outer areas and strike-slip located in specific areas, while in some regions, different styles of faulting coexist in close proximity with different focal mechanism orientations. Overall, the different style of faulting are distributed in about 33 per cent NF, 35 per cent TF and 32 per cent SS. Figure 3. View largeDownload slide The prevailing moment tensor computed in each cell shown as focal mechanism. The red, blue and green lower hemisphere focal mechanisms correspond to the weighted focal mechanisms obtained and classified as normal (NF), reverse (TF) and strike-slip (SS) faulting, respectively. Figure 3. View largeDownload slide The prevailing moment tensor computed in each cell shown as focal mechanism. The red, blue and green lower hemisphere focal mechanisms correspond to the weighted focal mechanisms obtained and classified as normal (NF), reverse (TF) and strike-slip (SS) faulting, respectively. In Fig. 4, we show for each cell the conditional probabilities of the different expected faulting styles, as from eqs (6) to (8). In particular, the computed conditional probabilities associated to the style of faulting are represented by a three slices pie chart representing the NF (red), TF (blue) and SS (green) probability of occurrence, for each cell. Figure 4. View largeDownload slide Pie charts resulting from the computation conditional probability for the next NF (red), TF (blue) and SS (green) events expected for each cell. Figure 4. View largeDownload slide Pie charts resulting from the computation conditional probability for the next NF (red), TF (blue) and SS (green) events expected for each cell. In Fig. 5, we show the SHmax forecasts, which describe well the tectonics complexity discussed in the previous section of the paper (cf. Section 2 and Fig. 1). Figure 5. View largeDownload slide SHmax orientation obtained for each cell after the TWMT and conditional probability computations. The orientations are coloured according to the tectonic regime (red, NF; green, SS and blue, TF). Figure 5. View largeDownload slide SHmax orientation obtained for each cell after the TWMT and conditional probability computations. The orientations are coloured according to the tectonic regime (red, NF; green, SS and blue, TF). In Fig. 6 (and for details Fig. S1, Supporting Information), we show the accuracy of the results according the three-classes scheme described before; in particular, results belonging to ‘Class 1’, ‘Class 2’ and ‘Class 3’ are represented in white, yellow and orange dots, respectively. Figure 6. View large Download slide Map of the accuracy classes based on the total contribution of weights in each cell (eq. 7): (i) if $$C_k^{( {{\rm{TOT}}} )}$$≤ 33th percentile of the distribution of $$C_k^{( {{\rm{TOT}}} )}$$ for all cells, the kth cell belongs to ‘Class 1’; (ii) if $$C_k^{( {{\rm{TOT}}} )}$$ is comprised between 33th and 66th percentile the cell belongs to ‘Class 2’ and (iii) if $$C_k^{( {{\rm{TOT}}} )}$$ ≥ 66th percentile the cell belongs to ‘Class 3’ (for statistical distribution details see Fig. S1, Supporting Information). Figure 6. View large Download slide Map of the accuracy classes based on the total contribution of weights in each cell (eq. 7): (i) if $$C_k^{( {{\rm{TOT}}} )}$$≤ 33th percentile of the distribution of $$C_k^{( {{\rm{TOT}}} )}$$ for all cells, the kth cell belongs to ‘Class 1’; (ii) if $$C_k^{( {{\rm{TOT}}} )}$$ is comprised between 33th and 66th percentile the cell belongs to ‘Class 2’ and (iii) if $$C_k^{( {{\rm{TOT}}} )}$$ ≥ 66th percentile the cell belongs to ‘Class 3’ (for statistical distribution details see Fig. S1, Supporting Information). It is worth stressing that, in general, the quality of the forecasts is unavoidably related to the number of input information. While it is obvious that the larger the number of data, the better, conversely it is not possible to identify the minimum number of information above which the forecasts can be considered reliable. The only way to evaluate the forecasts and to validate a model is through the comparison with independent data (e.g. Marzocchi & Jordan 2014); if the independent data set is limited, also a qualitative comparison between forecasts and the geological knowledge of the territory may increase the confidence on the quality of the forecasts. This is what we do in the next section. 5 DISCUSSION AND CONCLUSIONS In this paper, we provide spatial forecasts of the focal mechanism of the future moderate-large earthquake in a spatial grid 0.1°–0.1° that covers the whole Italian territory. One of the main applications of these forecasts is to contribute to reduce the epistemic uncertainty in PSHA. In fact, it has been proposed that earthquakes with the same magnitude and distance from a specific site induce different ground shaking as a function of the focal mechanism that characterize them (e.g. Campbell 1984; Bommer et al. 2003; Convertito & Herrero 2004; Convertito & Herrero 2006; Strasser et al. 2006; Roselli et al. 2016): on average, ground shaking caused by reverse earthquakes is larger than ground shaking caused by same magnitude and distance strike-slip earthquakes that, in turn, is larger than NF earthquakes (Campbell 1984; Strasser et al.2006). By using the TWMT, we map the results obtained for each cell along the entire Italian territory with different degrees of accuracy. The results allow us defining (i) the expected focal mechanism (Tables S1–S3, Supporting Information) and the faulting style, normal, reverse or strike-slip (Fig. 3); (ii) their probability of occurrence (Fig. 4); (iii) the SHmax orientation map (Fig. 5) as a function of the tectonic regimes. The forecasts of Figs 3–5 highlight some interesting features. Moving from north to south (Fig. 5 and subordinately Figs 3 and 4) and considering only the most likely focal mechanism solution for each cell, the results show that the Italian northern sector is characterized by a strong inhomogeneity mainly because of the presence of three different tectonic regimes (see Figs 3 and 5) and, only to a lesser extent because of the SHmax orientation. The latter (Fig. 5) looks uniform, N–S oriented, along the central and eastern part of this sector (Po Plain and Friuli area); the western part however is characterized by a not homogeneous SHmax both in tectonic regime and in orientation except for local areas (less than 100 km length). The Apennines—from Tuscany to Calabria region—show a wide distribution of NF mechanisms mainly aligned with the NW–SE Apennine belt. Only along the coastal Tyrrhenian areas beside to NF mechanisms, local strike-slip mechanisms are present with different SHmax orientations. Along the Adriatic side, the reverse faulting mechanisms characterize the most part of the Adriatic foredeep from the Po Plain up to Gargano area. Strike-slip mechanisms are also present but restricted to few zones. The SHmax orientations well depict the sectors with northward and NE compressions almost reaching the Dinarides. In the Calabria–Sicily region, the SHmax rotation following the natural curvature of the Calabrian arc is very well defined with NF mechanisms. The Sicilian Tyrrhenian zone is comparable with the previous Po Plain sector characterized by N-S compression and prevalent reverse faulting mechanisms. Finally, along the Ionian Sea relative to Calabria and Sicily regions is defined a narrow area characterized by SS mechanism and regular NW SHmax orientations. To verify the reliability of the forecasts, we carry out a qualitative evaluation of the forecasts comparing them with testing data, not previously used to calibrate the model. We use nine earthquakes with Mw ≥ 3.9 occurred during 2016 in seven different Italian regions (Fig. 1), whose focal mechanism solutions are relative to the Time Domain Moment Tensor Catalogue (http://cnt.rm.ingv.it/en/tdmt). In Fig. 7, we show the observed (black lower hemisphere focal mechanisms) and the forecast NF (red) TF (blue) and SS (green) focal solutions. Moreover, we associate to each of them, the corresponding pie chart in the centre of cells, where the slices show the percentage of probability of occurrence associated to NF (light red slices) TF (light blue slices) and SS (light green slices) expected stress regime. Below, we describe each specific testing earthquake. Reggio Emilia (Fig. 7a): The Mw 4.0 Reggio Emilia earthquake has a NF mechanism and occurred very close to the boundary where NF kinematics moves toward a compressional tectonics. In fact, the seismic event is located in the middle of a cell showing normal and compressive focal mechanisms with consistent orientation of nodal planes. Terni (Fig. 7b): The forecast for the area around Terni Mw 4.1 seismic event shows that the most likely mechanism is NF (≈70 per cent), with a lower probability for strike-slip mechanism (≈30 per cent). The mechanism of the observed seismic event is then in agreement with the forecast of the kinematics and orientations. Amatrice (Fig. 7c): For the ongoing central Apennine seismic sequence of August 24 (Roselli & Mariucci 2016), we consider only three earthquakes relative to 2016 with M ≥ 5.5 that are the most energetic released during the sequence, because almost all the earthquakes have the same NW-NF kinematics. The three earthquakes fit well the forecast of the focal mechanisms and the expected orientation of the faults. Firenze (Fig. 7d): Although with Mw 3.9, we have also considered this event because it occurred in an area usually characterized by few earthquakes and located at ∼30 km southwest of Firenze town (Fig. 1). The strike-slip event agrees with the forecasts of the model. Campobasso (Fig. 7e): The Mw 4.3 Campobasso event shows an NW- NF mechanism. The earthquake is located in the middle of cells showing normal and strike-slip mechanisms. The orientation of T axes is in agreement with the observation. Siracusa (Fig. 7f): This Mw 4.2 strike-slip earthquake is located in a cell showing a prevalent forecast of compressional faulting, with only a minor strike-slip component. However, nodal planes (∼N–S and E–W oriented) and tensional/compressional axis orientations are in agreement with the forecast of the model. In any case, we note that the accuracy of the regions is very low (see Fig. 6), hence some discrepancy may be expected. Ionio (Fig. 7g): This Mw 4.0 strike-slip earthquake, although located at the boundary of the considered area, fits very well the forecast of the nodal plane and its kinematics. Figure 7. View largeDownload slide Comparison between nine observed (black) and forecast (coloured) earthquake focal mechanisms in seven different zones of Italian territory. Red, blue and green lower hemisphere focal mechanisms represent the synthetic NF, TF and SS focal mechanisms computed for the corresponding cell. In the centre of each cell, the slices of the pie chart show the percentage associated to the expected normal (red slices), reverse (blue slices) and strike-slip (green slices) faulting regime 2016 earthquakes: (a) Reggio Emilia (inner northern Apennine, Mw 4.0 December 9), (b) Terni (central Apennine, Mw 4.1 May 30), (c) Amatrice (central Apennine, Mw 6.0 August 24, Mw 5.9 October 26 and Mw 6.5 October 30), (d) Firenze (Tuscany, Mw 3.9 October 25), (e) Campobasso (Molise, Mw 4.3, January 16), (f) Siracusa (Sicily, Mw 4.2 February 8) and (g) Ionio (Ionian-Sea, Mw 4.0 March 6). Figure 7. View largeDownload slide Comparison between nine observed (black) and forecast (coloured) earthquake focal mechanisms in seven different zones of Italian territory. Red, blue and green lower hemisphere focal mechanisms represent the synthetic NF, TF and SS focal mechanisms computed for the corresponding cell. In the centre of each cell, the slices of the pie chart show the percentage associated to the expected normal (red slices), reverse (blue slices) and strike-slip (green slices) faulting regime 2016 earthquakes: (a) Reggio Emilia (inner northern Apennine, Mw 4.0 December 9), (b) Terni (central Apennine, Mw 4.1 May 30), (c) Amatrice (central Apennine, Mw 6.0 August 24, Mw 5.9 October 26 and Mw 6.5 October 30), (d) Firenze (Tuscany, Mw 3.9 October 25), (e) Campobasso (Molise, Mw 4.3, January 16), (f) Siracusa (Sicily, Mw 4.2 February 8) and (g) Ionio (Ionian-Sea, Mw 4.0 March 6). These results show a good agreement between the forecasts and the focal mechanism solution of independent earthquakes, supporting the reliability of the forecasting procedure. This is an important precondition for any practical use of such forecasts, such as, for example, for their use in the next PSHA model for Italy under development (Meletti et al.2017). 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The role of the passive sinking of a relic lithospheric slab, in The lithosphere in Italy , Vol. 80, pp. 157– 176, Advances in Earth Science Research, Italian National Committee for the International Lithosphere Program, Atti Convegni Lincei. Pierdominici S., Heidbach O., 2012. Stress field of Italy—mean stress orientation at different depths and wave-length of the stress pattern, Tectonophysics , 532, 301– 311. Google Scholar CrossRef Search ADS   Pondrelli S., Salimbeni S., Ekström G., Morelli A., Gasperini P., Vannucci G., 2006. The Italian CMT dataset from 1977 to the present, Phys. Earth planet. Inter. , 159( 3–4), 286– 303. Google Scholar CrossRef Search ADS   Roselli P., Mariucci M.T., 2016. Preliminary earthquake focal mechanism forecasts for the Amatrice sequence (central Italy), Ann. Geophys. , 59(Fast Track 5), doi:10.4401/ag-7306. Roselli P., Marzocchi W., Faenza L., 2016. Toward a new probabilistic framework to score and merge Ground-Motion Prediction Equations: the case of the Italian region, Bull. seism. Soc. Am. , 106( 2), 720– 733. Google Scholar CrossRef Search ADS   Royden L.E., Patacca E., Scandone P., 1987. Segmentation and configuration of subducted lithosphere in Italy: an important control on thrust-belt and foredeep-basin evolution, Geology , 15, 714– 717. Google Scholar CrossRef Search ADS   Scrocca D., Doglioni C., Innocenti F., 2003. Constraints for an interpretation of the Italian geodynamics: a review, Mem. Desc. Carta Geol. Ital. , 62, 15– 46. Selva J., Marzocchi W., 2004. Focal parameters, depth estimation, and plane selection of the worldwide shallow seismicity with Ms ≥ 7.0 for the period 1900–1976, Geochem. Geophys. Geosyst. , 5( 5), 1525– 2027. Google Scholar CrossRef Search ADS   Selvaggi G., Amato A., 1992. Subcrustal earthquakes in the northern Apennines (Italy): evidence for a still active subduction?, Geophys. Res. Lett. , 19, 2127– 2130. Google Scholar CrossRef Search ADS   Strasser F.O., Montaldo V., Douglas J., Bommer J.J., 2006. Comment on ‘Influence of Focal Mechanism in Probabilistic Seismic Hazard Analysis’ by Vincenzo Convertito and Andrè Herrero, Bull. seism. Soc. Am. , 96( 2), 750– 753. Google Scholar CrossRef Search ADS   Wortel M.J.R., Spakman W., 2000. Subduction and slab detachment in the Mediterranean-Carpathian region, Science , 290, 1910– 1917. Google Scholar CrossRef Search ADS PubMed  Zoback M.L., 1992. First- and second-order patterns of stress in the lithosphere: the world stress map project, J. geophys. Res. , 97( B8), 703– 728. Zoback M.L., Zoback M.D., 1980. State of stress in the conterminous United States, J. geophys. Res. , 85( B11), 6113– 6156. Google Scholar CrossRef Search ADS   SUPPORTING INFORMATION Supplementary data are available at GJI online. Figure S1. Distribution of C(TOT) and the related position of 33th and 66th percentiles shown in Fig. 6. (a) Histogram of the C(TOT) values obtained from eq. (7), where the 33th (magenta line) and 66th (yellow line) percentiles are shown. (b) Empirical distribution of the C(TOT) values obtained from eq. (7). Table S1. List of 1604 cell coordinates with expected depths, moment tensors and probability of occurrence for each faulting style with prevailing NF, computed by using the TWMT. Table S2. List of 1949 cell coordinates with expected depths, moment tensors and probability of occurrence for each faulting style with prevailing TF, computed by using the TWMT. Table S3. List of 1565 cell coordinates with expected depths, moment tensors and probability of occurrence for each faulting style with prevailing SS, computed by using the TWMT. Please note: Oxford University Press is not responsible for the content or functionality of any supporting materials supplied by the authors. Any queries (other than missing material) should be directed to the corresponding author for the paper. © The Authors 2017. Published by Oxford University Press on behalf of The Royal Astronomical Society. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Geophysical Journal International Oxford University Press

Earthquake focal mechanism forecasting in Italy for PSHA purposes

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Oxford University Press
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© The Authors 2017. Published by Oxford University Press on behalf of The Royal Astronomical Society.
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0956-540X
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Abstract

SUMMARY In this paper, we put forward a procedure that aims to forecast focal mechanism of future earthquakes. One of the primary uses of such forecasts is in probabilistic seismic hazard analysis (PSHA); in fact, aiming at reducing the epistemic uncertainty, most of the newer ground motion prediction equations consider, besides the seismicity rates, the forecast of the focal mechanism of the next large earthquakes as input data. The data set used to this purpose is relative to focal mechanisms taken from the latest stress map release for Italy containing 392 well-constrained solutions of events, from 1908 to 2015, with Mw ≥ 4 and depths from 0 down to 40 km. The data set considers polarity focal mechanism solutions until to 1975 (23 events), whereas for 1976–2015, it takes into account only the Centroid Moment Tensor (CMT)-like earthquake focal solutions for data homogeneity. The forecasting model is rooted in the Total Weighted Moment Tensor concept that weighs information of past focal mechanisms evenly distributed in space, according to their distance from the spatial cells and magnitude. Specifically, for each cell of a regular 0.1° × 0.1° spatial grid, the model estimates the probability to observe a normal, reverse, or strike-slip fault plane solution for the next large earthquakes, the expected moment tensor and the related maximum horizontal stress orientation. These results will be available for the new PSHA model for Italy under development. Finally, to evaluate the reliability of the forecasts, we test them with an independent data set that consists of some of the strongest earthquakes with Mw ≥ 3.9 occurred during 2016 in different Italian tectonic provinces. Europe, Earthquake ground motions, Earthquake interaction, forecasting, and prediction, Seismicity and tectonics, Statistical seismology 1 INTRODUCTION Probabilistic seismic hazard analysis (PSHA) is based on the forecast of seismicity in the next decades (the seismicity rate models) coupled with the use of ground motion prediction equations (GMPEs) to estimate the ground shaking caused by the expected earthquakes. The link between seismicity rate models and GMPEs is not always straightforward, because many common seismicity rate models estimate the expected number of earthquakes in each space and magnitude bin, while the most recent GMPEs need additional information, such as, for example, the expected style of faulting. This lack of information may affect PSHA, where a reasonable set of different seismicity rate models and GMPEs has to be considered altogether to quantify and to model the so-called epistemic uncertainty (Marzocchi et al.2015). For instance, the new ongoing seismic hazard model for Italy is planning to consider a set of seismicity rate models and different GMPEs, but most of the seismicity rate models do not provide a forecast of the style of faulting (Meletti et al.2017). Motivated by this lack, in this paper, we propose a forecast of the earthquake focal mechanism in Italy, from which the style of faulting and possibly the geometry of the expected ruptures may be derived. This forecasting model is built independently from the seismicity rate models, hence it can be easily coupled with the outcome of any seismicity rate model that does not provide such a kind of information. Eventually, this forecast is going to facilitate the use of all GMPEs with all seismicity rate models for PSHA purposes. Although we focus our attention on the Italian region, the adopted procedure is quite general, and it can be applied to any other country or geographical region. Italy is characterized by complex tectonics, which leads to a large spatial variability of the observed style of faulting. Although information of different nature is available to characterize the tectonics variability, in this paper we aim to forecast the focal mechanism of future earthquakes, and so, we use only the focal mechanisms of past earthquakes under the assumption that the main tectonic features remain stable over decades. The focal mechanism forecast for future large earthquakes is based on a procedure developed by Selva & Marzocchi (2004), which was inspired by the concept of total moment tensor proposed by Kostrov (1974). In the next sections, we briefly introduce the Italian tectonics setting and then describe, in detail, the data set used and the methodology. Finally, we show and discuss the results in comparison to the main Italian tectonic features in order to evaluate the quality of produced results. 2 ITALIAN TECTONIC SETTING The geodynamic setting of the Italian region is characterized by a complex interaction of different mechanisms, mainly related to the continental collision between Africa and Eurasia plates and by the presence of smaller intervening microplates (Fig. 1). A fundamental role has been played by Adria microplate that has complicated and influenced the tectonic processes, the distribution of seismicity and also the volcanic activity. In this convergence context, which is going on since the Early Tertiary, an Adriatic-Ionian lithosphere subduction beneath the Alps (to the north), Dinarides (to the east) and Apennines (to the west) has developed (Malinverno & Ryan 1986; Royden et al.1987; Ghisetti & Vezzani 1999; Faccenna et al.2001; Scrocca et al.2003). Figure 1. View largeDownload slide Tectonic sketch map of Italy with main thrust, normal and strike-slip faults (modified after Meletti et al.2000). In particular, letters in ‘bold’ indicates the epicentres of the 2016 strongest earthquakes (Mw ≥ 3.9) used as testing data (see also Table 4 and Fig. 7). Figure 1. View largeDownload slide Tectonic sketch map of Italy with main thrust, normal and strike-slip faults (modified after Meletti et al.2000). In particular, letters in ‘bold’ indicates the epicentres of the 2016 strongest earthquakes (Mw ≥ 3.9) used as testing data (see also Table 4 and Fig. 7). The actual mechanisms linked to the subduction process and to the complex slab geometry beneath the Apennines are still debated (Carminati & Doglioni 2012), including slab sinking (Mitrovica et al.1989), slab rollback (Carminati et al.2003; Carminati & Doglioni 2012), slab break off (Wortel & Spakman 2000) and slab-induced return flow (Faccenna & Becker 2010). In particular, as documented by tomography and also suggested by the absence of intermediate/deep seismicity, at depth the Adriatic slab is no longer intact: in the central and southern Apennines, the lithospheric slab is likely detached and the subduction has ended (Amato et al.1993; Lucente et al.1999; Wortel & Spakman 2000; De Gori et al.2001; Cimini & Marchetti 2006; Di Stefano et al. 2009). On the contrary, clear evidence of an oceanic slab is well documented by the occurrence of intermediate and deep seismicity beneath the southern Tyrrhenian basin with earthquakes located along a narrow 200-km-wide Benioff zone. The present-day regional geodynamic setting is then mainly characterized by the relation occurring between subduction and backarc extension (Karig 1971) and by the eastward/south-eastward rollback of the slab that led to the development of the thrust belt-foredeep Apennine system (among many others: Malinverno & Ryan 1986; Royden et al.1987; Patacca & Scandone 1989; Doglioni 1991; Carminati et al.2002; Faccenna et al.2003; Di Stefano et al.2009). The eastward migrating subduction hinge with the progressive retreat of the slab produced compression at the outer front and contemporaneous extension in the backarc Tyrrhenian region (e.g. Selvaggi & Amato 1992; Frepoli & Amato 1997; Lucente et al.1999; Cimini & Marchetti 2006). In the northern Apennines, the extension compression pair—eastward migrating from late Miocene—is still observable (e.g. Lavecchia et al.1994; Frepoli & Amato 1997; Mariucci et al.1999), whereas in the central-southern Apennines a prevailing extension is evident, at least since middle Pleistocene (e.g. Meletti et al.2000). Such a complex tectonic setting represents a challenge to provide reliable focal mechanism forecasts for the next earthquakes. 3 DATA AND METHOD 3.1 Input data: focal mechanisms and gridding The latest Italian data set of the contemporary stress field in the crust consists of 855 stress indicators: single earthquake focal mechanisms, data from formal inversion of earthquake focal mechanisms, borehole breakouts, mapped active faults and overcoring data (Montone & Mariucci 2016; Mariucci & Montone 2017). Each datum is quality-ranked according to the World Stress Map Project rules (http://www.world-stress-map.org; Heidbach et al.2010), from A the best to D the worst. ‘A’ quality means that the orientation is believed to be within ±15°, ‘B’ ±15°–20°, ‘C’ ±20°–25°, ‘D’ ±25–40° (a questionable orientation) and quality ‘E’ denotes unreliable information (>40°). Among all stress indicators currently available for Italy, in this work we select and use only the focal mechanism data, because they are more suitable for the purpose of this paper. Such focal mechanisms are taken from the latest stress map release for Italy (Montone & Mariucci 2016) which contains 392 well-constrained (C quality data) solutions of events (see Fig. 2), from 1908 to 2015, with Mw ≥ 4 and depths within the uppermost 40 km (85 per cent of hypocentres with depth ≤ 20 km). For the period 1908–1975, the data set considers polarity focal mechanism solutions (only 23 events), whereas for 1976–2015, it takes into account only the Centroid Moment Tensor (CMT)-like earthquake focal solutions for data homogeneity (European-Mediterranean Regional Centroid Moment Tensor database, http://www.bo.ingv.it/RCMT/; and ‘The Italian CMT dataset from 1976 to the present’, http://www.bo.ingv.it/RCMT/, Pondrelli et al.2006). Figure 2. View largeDownload slide Location map of 392 Mw ≥ 4 focal mechanisms (training data) split in 179 NF, 128 TF and 85 SS (red, blue and green lower hemisphere focal mechanisms, respectively), from 1908 to 2015. The grey points indicate the 8993 centres of the cells where the TWMTs have been computed. Black lines represent the main tectonic structures (DISS Working Group 2015). Figure 2. View largeDownload slide Location map of 392 Mw ≥ 4 focal mechanisms (training data) split in 179 NF, 128 TF and 85 SS (red, blue and green lower hemisphere focal mechanisms, respectively), from 1908 to 2015. The grey points indicate the 8993 centres of the cells where the TWMTs have been computed. Black lines represent the main tectonic structures (DISS Working Group 2015). At first approximation the elastic strain can be considered directly related to stress and the P, B and T axes are assumed to be equal to σ1, σ2 and σ3, respectively (e.g. Zoback & Zoback 1980). Assuming one of the three principal stresses as vertical, the other two lie on the horizontal plane and are defined as maximum and minimum horizontal stress (SHmax and Shmin), according to their relative magnitude. SHmax corresponds to σ1 [thrust (TF) and strike-slip faulting (SS) regime] or σ2 [normal faulting (NF) regime]. The principle axes of the derived moment tensor (compression P, null B and extension T) fully describe the focal mechanisms. Regional compilations of earthquake focal mechanisms show that the average orientation for compression (P), null (B) and extension (T) axes provides a good indication of the stress orientation along a region (e.g. Zoback & Zoback 1980). In order to identify the tectonic regime (according to Anderson 1951), we use a classification criterion related to the plunge of the P, T and B axes (see table 3 in Zoback 1992), discarding all the focal solutions with P, T and B axes that do not define a clear tectonic regime. We group the data into the three main tectonic regime categories: NF, TF and SS to perform our calculations for each group separately. The few ‘oblique’ focal mechanisms (17), classified with an intermediate regime (normal strike, NS and thrust strike, TS), are redistributed into the three main categories on the basis of the maximum plunge of the axes, considering that the vertical axis is P/σ1 for NF, T/σ3 for TF and B/σ2 for SS and also taking into account the most geologically plausible criterion. After this classification, our training data set consists of 179 NF, 128 TF and 85 SS faulting focal mechanisms (see Tables 1–3). Fig. 2 shows the location map and types of focal mechanisms as normal (red), thrust (blue) and strike-slip (green) lower hemisphere focal mechanisms, respectively. Table 1. List of 179 earthquakes selected as input data and classified as normal faulting focal mechanisms (NF, red lower hemisphere focal mechanisms in Fig. 2). Date  Lat (°)  Lon (°)  Depth (km)  Mw  Strike1 (°)  Dip1 (°)  Rake1 (°)  Strike2 (°)  Dip2 (°)  Rake2 (°)  1908 December 28  38.12  15.60  10.0  7.0  349  42  − 122  209  55  − 64  1915 January 13  41.99  13.65  8.0  6.9  135  63  − 90  315  26  − 89  1930 July 23  41.05  15.36  15.0  6.7  280  50  − 80  84  41  − 101  1939 February 11  44.07  11.65  7.0  4.7  310  49  − 120  171  49  − 60  1939 October 15  44.23  10.20  27.0  4.9  175  26  − 126  33  69  − 74  1941 March 16  38.44  12.12  20.0  6.9  217  39  − 76  19  52  − 101  1958 June 24  42.35  13.44  10.0  5.0  22  37  − 57  162  59  − 112  1962 August 21  41.13  14.95  8.0  5.7  310  65  − 130  201  54  − 31  1962 August 21  41.08  15.00  8.0  6.1  310  65  − 110  186  41  − 40  1967 December 09  42.00  16.50  33.0  4.7  277  74  − 90  97  15  − 89  1971 February 06  42.31  11.76  2.0  4.6  279  44  − 133  151  59  − 56  1971 February 12  43.23  12.49  33.0  4.5  290  48  − 139  169  60  − 50  1974 December 02  42.82  12.93  5.0  4.8  195  48  − 44  317  58  − 128  1977 June 05  37.88  14.46  10.0  4.6  61  26  − 139  293  73  − 70  1978 March 11  38.10  16.03  33.0  5.2  270  41  − 72  66  52  − 105  1978 July 30  42.65  12.46  10.0  4.4  209  42  − 55  345  57  − 117  1979 September 19  42.81  13.06  16.0  5.8  183  28  − 70  341  64  − 100  1980 February 20  39.30  16.21  12.0  4.3  14  43  − 78  178  48  − 101  1980 March 09  39.94  16.12  19.0  4.7  157  35  − 80  324  56  − 97  1980 May 14  40.46  15.85  24.0  4.8  119  38  − 112  326  56  − 74  1980 June 07  44.09  10.72  16.0  4.6  334  23  − 50  112  72  − 105  1980 June 09  42.29  13.88  20.0  4.7  266  37  − 88  84  53  − 91  1980 June 14  41.85  13.73  8.0  5.0  296  37  − 90  116  53  − 90  1980 November 23  40.91  15.37  10.0  6.9  135  41  − 80  303  50  − 98  1980 November 24  40.89  15.26  10.0  5.0  131  29  − 110  333  63  − 79  1980 November 25  40.70  15.47  10.0  4.9  129  26  − 65  281  67  − 102  1980 November 25  40.65  15.40  10.0  5.4  122  30  − 119  335  64  − 74  1981 January 16  40.95  15.37  15.0  5.2  115  30  − 93  298  60  − 89  1981 November 29  40.74  15.64  33.0  4.5  104  41  − 138  340  64  − 58  1982 March 21  39.70  15.64  18.9  5.2  15  39  − 127  239  60  − 64  1982 August 15  40.81  15.36  10.0  4.7  158  48  − 45  282  59  − 128  1982 October 17  43.12  12.59  13.0  4.6  132  39  − 125  354  59  − 65  1982 October 17  43.16  12.59  16.0  4.6  137  34  − 128  0  64  − 68  1982 October 18  43.13  12.63  19.0  4.6  143  27  − 131  8  70  − 71  1983 August 12  41.75  13.85  10.0  4.8  104  46  − 115  318  49  − 66  1984 April 22  43.62  10.19  15.0  4.6  349  38  − 67  141  56  − 107  1984 April 29  43.27  12.57  14.0  5.6  143  21  − 72  304  70  − 97  1984 May 07  41.77  13.89  10.0  5.9  174  31  − 52  312  66  − 110  1984 May 11  41.83  13.95  13.0  5.5  156  43  − 76  317  49  − 103  1986 October 01  44.34  10.19  28.0  4.5  135  43  − 91  316  47  − 90  1987 January 28  40.95  15.47  10.0  4.5  160  45  − 79  326  46  − 100  1987 July 05  43.78  12.23  11.0  4.5  298  43  − 83  108  48  − 97  1988 January 08  40.08  16.01  10.0  4.7  148  30  − 86  324  60  − 92  1993 June 05  43.12  12.68  8.0  4.6  139  37  − 108  341  55  − 77  1995 August 24  44.13  10.76  34.0  4.5  117  47  − 111  327  47  − 69  1996 April 03  40.76  15.49  10.0  4.9  123  30  − 110  325  62  − 79  1996 October 20  42.60  13.28  10.0  4.3  128  31  − 119  341  63  − 74  1996 December 14  37.81  13.84  40.0  4.3  123  23  − 43  254  74  − 108  1997 March 19  41.40  14.63  10.0  4.5  280  27  − 110  122  65  − 80  1997 September 03  43.01  12.90  10.2  4.5  137  30  − 88  315  60  − 91  1997 September 26  43.02  12.89  10.0  5.7  321  44  − 98  152  46  − 83  1997 September 26  43.03  12.85  10.0  6.0  144  42  − 80  312  49  − 98  1997 September 26  43.01  12.97  10.0  4.5  147  29  − 88  325  61  − 91  1997 September 26  43.06  12.85  10.0  4.3  193  45  − 43  316  61  − 126  1997 September 27  43.09  12.81  5.5  4.3  326  35  − 92  148  55  − 89  1997 September 27  43.02  12.83  10.0  4.2  288  36  − 135  160  66  − 63  1997 September 27  43.06  12.77  10.0  4.3  136  35  − 80  304  56  − 97  1997 October 02  43.64  12.14  10.0  4.4  158  41  − 58  298  56  − 115  1997 October 03  43.03  12.84  10.0  5.2  141  43  − 74  300  49  − 104  1997 October 04  42.90  12.90  10.0  4.4  299  42  − 101  133  49  − 81  1997 October 04  42.93  12.86  10.0  4.4  322  33  − 52  99  64  − 112  1997 October 04  42.94  12.93  10.0  4.7  318  42  − 80  125  49  − 99  1997 October 04  42.93  12.90  10.0  4.4  329  43  − 77  131  48  − 102  1997 October 06  43.02  12.84  10.0  5.4  145  40  − 80  312  51  − 98  1997 October 07  42.99  12.82  11.6  4.2  126  26  − 102  319  65  − 84  1997 October 07  43.03  12.85  10.0  4.5  141  42  − 77  304  49  − 101  1997 October 12  42.91  12.94  10.0  5.2  321  40  − 100  154  51  − 82  1997 October 12  42.86  12.97  10.0  4.3  271  14  − 133  136  80  − 80  1997 October 13  42.90  13.00  10.0  4.3  315  37  − 73  115  54  − 102  1997 October 13  42.89  12.92  10.0  4.4  305  35  − 96  133  56  − 86  1997 October 14  42.93  12.92  10.0  5.6  122  38  − 100  314  52  − 82  1997 October 15  42.93  12.89  10.0  4.4  329  40  − 65  117  55  − 110  1997 October 16  42.91  12.92  10.0  4.3  310  11  − 80  120  79  − 92  1997 October 16  42.98  12.89  10.0  4.1  118  35  − 88  295  55  − 92  1997 October 16  42.88  12.97  10.0  4.3  305  33  − 123  163  63  − 70  1997 October 17  42.89  12.91  10.0  4.2  326  48  − 53  97  54  − 124  1997 October 19  42.97  12.79  10.0  4.2  128  44  − 103  326  47  − 78  1997 October 25  42.84  13.01  10.0  4.3  333  33  − 54  112  64  − 111  1997 November 09  42.87  13.00  10.0  4.9  118  46  − 113  329  48  − 68  1997 November 30  42.88  12.95  10.0  4.3  125  36  − 119  339  59  − 70  1997 December 24  44.09  10.55  10.0  4.3  95  49  − 132  329  56  − 53  1997 December 31  42.87  12.99  10.0  4.3  293  35  − 135  164  66  − 64  1998 February 07  43.00  12.90  10.2  4.4  308  36  − 98  138  55  − 84  1998 March 21  42.90  12.90  10.0  5.0  137  15  − 97  325  75  − 88  1998 April 03  43.16  12.70  10.0  5.1  142  30  − 106  341  61  − 81  1998 April 03  43.23  12.67  10.0  4.3  152  33  − 108  352  59  − 79  1998 April 05  43.18  12.76  10.0  4.8  138  31  − 98  327  59  − 85  1998 June 02  43.17  12.73  10.0  4.3  311  42  − 124  173  56  − 63  1998 June 25  43.00  12.80  10.0  4.0  96  47  − 123  319  52  − 60  1998 August 15  42.41  12.98  10.0  4.4  298  26  − 52  76  70  − 107  1998 September 09  40.03  15.98  10.0  5.6  139  29  − 83  311  61  − 94  1999 February 14  38.17  15.06  33.0  4.7  18  39  − 108  220  53  − 76  1999 July 07  44.29  10.90  10.0  4.7  314  40  − 44  80  64  − 121  1999 October 10  42.67  13.19  10.0  4.2  348  50  − 47  112  55  − 129  1999 December 29  46.60  10.31  10.0  4.8  320  43  − 99  152  47  − 82  1999 December 31  46.60  10.32  10.0  4.1  13  34  − 45  143  67  − 116  2000 April 01  42.89  11.74  10.0  4.5  309  38  − 49  81  63  − 117  2000 April 06  46.60  10.33  5.0  4.0  359  47  − 64  144  49  − 115  2000 August 21  44.87  8.48  10.0  4.9  146  39  − 71  302  53  − 105  2000 October 03  44.27  10.80  10.0  4.2  317  24  − 105  153  67  − 83  2000 December 16  42.65  12.66  10.0  4.2  273  35  − 76  76  56  − 100  2001 October 18  39.10  16.61  10.0  4.3  332  44  − 88  149  46  − 92  2001 November 25  37.91  13.96  20.0  4.7  137  31  − 57  280  64  − 108  2001 November 26  43.60  12.10  10.0  4.7  358  21  − 72  158  70  − 97  2002 February 21  43.76  12.05  7.0  4.1  313  35  − 86  128  55  − 93  2002 April 18  40.69  15.58  10.0  4.5  329  13  − 72  131  77  − 94  2003 January 26  43.88  11.96  6.0  4.7  140  41  − 101  336  50  − 80  2003 January 26  43.88  11.95  7.0  4.5  291  37  − 130  158  62  − 64  2005 April 18  44.71  9.35  0.0  4.0  336  34  − 35  96  71  − 118  2006 February 27  38.15  15.20  9.0  4.4  22  24  − 95  208  66  − 88  2006 April 17  43.64  10.23  10.0  4.2  323  50  − 53  94  52  − 125  2006 December 19  37.78  14.91  23.0  4.2  18  16  − 40  147  80  − 102  2007 August 18  38.22  15.17  12.0  4.5  347  34  − 120  201  61  − 71  2007 October 21  42.38  12.97  10.0  4.2  330  31  − 44  100  69  − 113  2008 March 01  44.06  11.25  10.0  4.7  278  36  − 123  136  60  − 68  2008 March 01  44.35  11.49  10.0  4.0  318  32  − 108  160  60  − 79  2008 March 01  44.06  11.22  5.0  4.2  326  43  − 67  116  51  − 110  2008 April 08  39.16  16.66  10.0  4.4  235  49  − 35  350  64  − 134  2008 October 24  44.34  7.36  10.0  4.1  308  51  − 150  198  67  − 43  2009 March 30  42.33  13.36  11.0  4.4  2  35  − 70  158  57  − 104  2009 April 05  42.36  13.37  10.0  4.2  147  37  − 108  349  55  − 77  2009 April 06  42.33  13.33  10.0  6.3  326  35  − 80  134  56  − 97  2009 April 06  42.41  13.32  10.0  5.1  355  46  − 53  128  55  − 122  2009 April 06  42.38  13.34  10.0  4.5  340  25  − 103  175  66  − 84  2009 April 06  42.35  13.37  10.0  4.2  138  41  − 93  323  49  − 87  2009 April 06  42.36  13.33  10.0  4.4  348  40  − 64  135  55  − 111  2009 April 06  42.45  13.36  10.0  5.1  341  44  − 68  132  50  − 109  2009 April 07  42.34  13.39  10.0  5.1  341  41  − 64  128  54  − 111  2009 April 07  42.28  13.46  15.0  5.5  105  53  − 134  342  55  − 48  2009 April 07  42.38  13.38  10.0  4.5  321  41  − 64  108  54  − 110  2009 April 08  42.30  13.43  10.0  4.0  344  38  − 84  156  52  − 95  2009 April 08  42.51  13.36  10.0  4.1  319  40  − 76  121  51  − 101  2009 April 09  42.48  13.34  15.0  5.4  329  45  − 81  136  46  − 99  2009 April 09  42.50  13.36  17.0  5.2  321  44  − 83  132  46  − 97  2009 April 09  42.44  13.42  10.0  4.3  113  57  − 144  2  61  − 39  2009 April 13  42.50  13.36  10.0  5.0  337  38  − 71  133  54  − 104  2009 April 14  42.53  13.28  10.0  4.0  309  42  − 92  132  48  − 88  2009 April 15  42.54  13.28  10.0  4.1  113  33  − 126  333  64  − 69  2009 April 23  42.25  13.49  10.0  4.1  126  43  − 105  326  49  − 76  2009 April 23  42.23  13.48  10.0  4.3  323  27  − 95  149  63  − 87  2009 June 22  42.45  13.36  14.0  4.7  113  19  − 112  315  72  − 83  2009 July 03  42.41  13.39  10.0  4.1  144  42  − 108  348  50  − 74  2009 July 12  42.34  13.38  10.0  4.3  342  35  − 76  146  56  − 99  2009 September 24  42.45  13.33  10.0  4.2  184  35  − 76  347  56  − 100  2009 November 08  37.83  14.55  15.0  4.5  310  21  − 54  92  73  − 102  2010 April 15  43.49  12.44  2.0  4.1  144  21  − 57  288  72  − 102  2010 June 16  38.83  16.14  15.0  4.1  109  50  − 38  225  62  − 133  2010 August 28  42.85  12.66  15.0  4.1  159  44  − 113  9  50  − 70  2010 September 17  41.49  15.63  30.1  4.3  148  45  − 25  256  73  − 132  2011 April 24  35.82  14.88  20.3  4.2  28  34  − 76  191  57  − 99  2011 May 24  43.86  12.03  5.0  4.2  266  52  − 132  142  54  − 49  2011 June 23  38.06  14.76  7.4  4.7  59  44  − 130  289  58  − 58  2011 July 06  38.01  14.80  7.5  4.1  115  44  − 53  249  56  − 120  2011 July 12  43.92  11.86  7.8  4.3  103  34  − 114  311  59  − 74  2011 July 12  43.92  11.85  7.4  4.2  109  37  − 102  304  54  − 81  2011 July 12  43.93  11.86  15.0  4.0  126  26  − 86  301  64  − 92  2011 July 25  44.98  7.28  25.1  4.7  264  28  − 60  50  66  − 105  2012 March 05  44.54  9.38  10.5  4.3  297  19  − 114  143  73  − 82  2012 March 15  42.81  13.20  6.0  4.0  297  36  − 99  128  54  − 83  2012 April 13  38.19  13.31  20.0  4.5  273  43  − 120  131  54  − 65  2012 May 28  39.86  16.12  3.0  4.5  137  31  − 119  350  63  − 74  2012 October 03  44.57  7.21  10.0  4.0  161  35  − 88  338  55  − 92  2012 October 25  39.88  16.01  15.0  5.3  162  40  − 84  334  50  − 95  2013 January 04  37.81  14.80  10.0  4.4  297  32  − 70  94  60  − 102  2013 February 16  41.71  13.58  11.0  4.9  309  47  − 118  168  50  − 63  2013 June 21  44.15  10.14  5.1  5.4  247  32  − 141  123  71  − 64  2013 June 21  44.16  10.15  10.0  4.3  325  49  − 54  97  52  − 124  2013 June 23  44.18  10.21  9.5  4.7  249  35  − 132  117  65  − 65  2013 June 30  44.17  10.20  9.8  4.8  281  21  − 91  102  69  − 90  2013 December 18  43.38  12.53  15.0  4.2  316  21  − 80  125  69  − 94  2013 December 22  43.38  12.52  10.0  4.3  158  22  − 54  301  73  − 103  2013 December 29  41.37  14.44  15.0  5.2  109  46  − 123  332  53  − 61  2014 January 20  41.36  14.45  11.0  4.4  137  29  − 65  289  64  − 103  2014 June 06  39.90  16.09  10.0  4.3  178  26  − 48  313  71  − 108  2014 April 07  44.47  6.69  5.0  4.9  29  40  − 68  181  54  − 107  2014 September 07  44.11  10.66  12.0  4.4  130  31  − 139  3  70  − 66  2014 December 28  39.29  16.36  11.0  4.5  14  40  − 84  186  50  − 95  2015 February 28  41.98  13.53  17.0  4.4  326  39  − 73  125  53  − 103  2015 August 03  39.16  16.53  26.0  4.2  255  49  − 46  20  57  − 128  Date  Lat (°)  Lon (°)  Depth (km)  Mw  Strike1 (°)  Dip1 (°)  Rake1 (°)  Strike2 (°)  Dip2 (°)  Rake2 (°)  1908 December 28  38.12  15.60  10.0  7.0  349  42  − 122  209  55  − 64  1915 January 13  41.99  13.65  8.0  6.9  135  63  − 90  315  26  − 89  1930 July 23  41.05  15.36  15.0  6.7  280  50  − 80  84  41  − 101  1939 February 11  44.07  11.65  7.0  4.7  310  49  − 120  171  49  − 60  1939 October 15  44.23  10.20  27.0  4.9  175  26  − 126  33  69  − 74  1941 March 16  38.44  12.12  20.0  6.9  217  39  − 76  19  52  − 101  1958 June 24  42.35  13.44  10.0  5.0  22  37  − 57  162  59  − 112  1962 August 21  41.13  14.95  8.0  5.7  310  65  − 130  201  54  − 31  1962 August 21  41.08  15.00  8.0  6.1  310  65  − 110  186  41  − 40  1967 December 09  42.00  16.50  33.0  4.7  277  74  − 90  97  15  − 89  1971 February 06  42.31  11.76  2.0  4.6  279  44  − 133  151  59  − 56  1971 February 12  43.23  12.49  33.0  4.5  290  48  − 139  169  60  − 50  1974 December 02  42.82  12.93  5.0  4.8  195  48  − 44  317  58  − 128  1977 June 05  37.88  14.46  10.0  4.6  61  26  − 139  293  73  − 70  1978 March 11  38.10  16.03  33.0  5.2  270  41  − 72  66  52  − 105  1978 July 30  42.65  12.46  10.0  4.4  209  42  − 55  345  57  − 117  1979 September 19  42.81  13.06  16.0  5.8  183  28  − 70  341  64  − 100  1980 February 20  39.30  16.21  12.0  4.3  14  43  − 78  178  48  − 101  1980 March 09  39.94  16.12  19.0  4.7  157  35  − 80  324  56  − 97  1980 May 14  40.46  15.85  24.0  4.8  119  38  − 112  326  56  − 74  1980 June 07  44.09  10.72  16.0  4.6  334  23  − 50  112  72  − 105  1980 June 09  42.29  13.88  20.0  4.7  266  37  − 88  84  53  − 91  1980 June 14  41.85  13.73  8.0  5.0  296  37  − 90  116  53  − 90  1980 November 23  40.91  15.37  10.0  6.9  135  41  − 80  303  50  − 98  1980 November 24  40.89  15.26  10.0  5.0  131  29  − 110  333  63  − 79  1980 November 25  40.70  15.47  10.0  4.9  129  26  − 65  281  67  − 102  1980 November 25  40.65  15.40  10.0  5.4  122  30  − 119  335  64  − 74  1981 January 16  40.95  15.37  15.0  5.2  115  30  − 93  298  60  − 89  1981 November 29  40.74  15.64  33.0  4.5  104  41  − 138  340  64  − 58  1982 March 21  39.70  15.64  18.9  5.2  15  39  − 127  239  60  − 64  1982 August 15  40.81  15.36  10.0  4.7  158  48  − 45  282  59  − 128  1982 October 17  43.12  12.59  13.0  4.6  132  39  − 125  354  59  − 65  1982 October 17  43.16  12.59  16.0  4.6  137  34  − 128  0  64  − 68  1982 October 18  43.13  12.63  19.0  4.6  143  27  − 131  8  70  − 71  1983 August 12  41.75  13.85  10.0  4.8  104  46  − 115  318  49  − 66  1984 April 22  43.62  10.19  15.0  4.6  349  38  − 67  141  56  − 107  1984 April 29  43.27  12.57  14.0  5.6  143  21  − 72  304  70  − 97  1984 May 07  41.77  13.89  10.0  5.9  174  31  − 52  312  66  − 110  1984 May 11  41.83  13.95  13.0  5.5  156  43  − 76  317  49  − 103  1986 October 01  44.34  10.19  28.0  4.5  135  43  − 91  316  47  − 90  1987 January 28  40.95  15.47  10.0  4.5  160  45  − 79  326  46  − 100  1987 July 05  43.78  12.23  11.0  4.5  298  43  − 83  108  48  − 97  1988 January 08  40.08  16.01  10.0  4.7  148  30  − 86  324  60  − 92  1993 June 05  43.12  12.68  8.0  4.6  139  37  − 108  341  55  − 77  1995 August 24  44.13  10.76  34.0  4.5  117  47  − 111  327  47  − 69  1996 April 03  40.76  15.49  10.0  4.9  123  30  − 110  325  62  − 79  1996 October 20  42.60  13.28  10.0  4.3  128  31  − 119  341  63  − 74  1996 December 14  37.81  13.84  40.0  4.3  123  23  − 43  254  74  − 108  1997 March 19  41.40  14.63  10.0  4.5  280  27  − 110  122  65  − 80  1997 September 03  43.01  12.90  10.2  4.5  137  30  − 88  315  60  − 91  1997 September 26  43.02  12.89  10.0  5.7  321  44  − 98  152  46  − 83  1997 September 26  43.03  12.85  10.0  6.0  144  42  − 80  312  49  − 98  1997 September 26  43.01  12.97  10.0  4.5  147  29  − 88  325  61  − 91  1997 September 26  43.06  12.85  10.0  4.3  193  45  − 43  316  61  − 126  1997 September 27  43.09  12.81  5.5  4.3  326  35  − 92  148  55  − 89  1997 September 27  43.02  12.83  10.0  4.2  288  36  − 135  160  66  − 63  1997 September 27  43.06  12.77  10.0  4.3  136  35  − 80  304  56  − 97  1997 October 02  43.64  12.14  10.0  4.4  158  41  − 58  298  56  − 115  1997 October 03  43.03  12.84  10.0  5.2  141  43  − 74  300  49  − 104  1997 October 04  42.90  12.90  10.0  4.4  299  42  − 101  133  49  − 81  1997 October 04  42.93  12.86  10.0  4.4  322  33  − 52  99  64  − 112  1997 October 04  42.94  12.93  10.0  4.7  318  42  − 80  125  49  − 99  1997 October 04  42.93  12.90  10.0  4.4  329  43  − 77  131  48  − 102  1997 October 06  43.02  12.84  10.0  5.4  145  40  − 80  312  51  − 98  1997 October 07  42.99  12.82  11.6  4.2  126  26  − 102  319  65  − 84  1997 October 07  43.03  12.85  10.0  4.5  141  42  − 77  304  49  − 101  1997 October 12  42.91  12.94  10.0  5.2  321  40  − 100  154  51  − 82  1997 October 12  42.86  12.97  10.0  4.3  271  14  − 133  136  80  − 80  1997 October 13  42.90  13.00  10.0  4.3  315  37  − 73  115  54  − 102  1997 October 13  42.89  12.92  10.0  4.4  305  35  − 96  133  56  − 86  1997 October 14  42.93  12.92  10.0  5.6  122  38  − 100  314  52  − 82  1997 October 15  42.93  12.89  10.0  4.4  329  40  − 65  117  55  − 110  1997 October 16  42.91  12.92  10.0  4.3  310  11  − 80  120  79  − 92  1997 October 16  42.98  12.89  10.0  4.1  118  35  − 88  295  55  − 92  1997 October 16  42.88  12.97  10.0  4.3  305  33  − 123  163  63  − 70  1997 October 17  42.89  12.91  10.0  4.2  326  48  − 53  97  54  − 124  1997 October 19  42.97  12.79  10.0  4.2  128  44  − 103  326  47  − 78  1997 October 25  42.84  13.01  10.0  4.3  333  33  − 54  112  64  − 111  1997 November 09  42.87  13.00  10.0  4.9  118  46  − 113  329  48  − 68  1997 November 30  42.88  12.95  10.0  4.3  125  36  − 119  339  59  − 70  1997 December 24  44.09  10.55  10.0  4.3  95  49  − 132  329  56  − 53  1997 December 31  42.87  12.99  10.0  4.3  293  35  − 135  164  66  − 64  1998 February 07  43.00  12.90  10.2  4.4  308  36  − 98  138  55  − 84  1998 March 21  42.90  12.90  10.0  5.0  137  15  − 97  325  75  − 88  1998 April 03  43.16  12.70  10.0  5.1  142  30  − 106  341  61  − 81  1998 April 03  43.23  12.67  10.0  4.3  152  33  − 108  352  59  − 79  1998 April 05  43.18  12.76  10.0  4.8  138  31  − 98  327  59  − 85  1998 June 02  43.17  12.73  10.0  4.3  311  42  − 124  173  56  − 63  1998 June 25  43.00  12.80  10.0  4.0  96  47  − 123  319  52  − 60  1998 August 15  42.41  12.98  10.0  4.4  298  26  − 52  76  70  − 107  1998 September 09  40.03  15.98  10.0  5.6  139  29  − 83  311  61  − 94  1999 February 14  38.17  15.06  33.0  4.7  18  39  − 108  220  53  − 76  1999 July 07  44.29  10.90  10.0  4.7  314  40  − 44  80  64  − 121  1999 October 10  42.67  13.19  10.0  4.2  348  50  − 47  112  55  − 129  1999 December 29  46.60  10.31  10.0  4.8  320  43  − 99  152  47  − 82  1999 December 31  46.60  10.32  10.0  4.1  13  34  − 45  143  67  − 116  2000 April 01  42.89  11.74  10.0  4.5  309  38  − 49  81  63  − 117  2000 April 06  46.60  10.33  5.0  4.0  359  47  − 64  144  49  − 115  2000 August 21  44.87  8.48  10.0  4.9  146  39  − 71  302  53  − 105  2000 October 03  44.27  10.80  10.0  4.2  317  24  − 105  153  67  − 83  2000 December 16  42.65  12.66  10.0  4.2  273  35  − 76  76  56  − 100  2001 October 18  39.10  16.61  10.0  4.3  332  44  − 88  149  46  − 92  2001 November 25  37.91  13.96  20.0  4.7  137  31  − 57  280  64  − 108  2001 November 26  43.60  12.10  10.0  4.7  358  21  − 72  158  70  − 97  2002 February 21  43.76  12.05  7.0  4.1  313  35  − 86  128  55  − 93  2002 April 18  40.69  15.58  10.0  4.5  329  13  − 72  131  77  − 94  2003 January 26  43.88  11.96  6.0  4.7  140  41  − 101  336  50  − 80  2003 January 26  43.88  11.95  7.0  4.5  291  37  − 130  158  62  − 64  2005 April 18  44.71  9.35  0.0  4.0  336  34  − 35  96  71  − 118  2006 February 27  38.15  15.20  9.0  4.4  22  24  − 95  208  66  − 88  2006 April 17  43.64  10.23  10.0  4.2  323  50  − 53  94  52  − 125  2006 December 19  37.78  14.91  23.0  4.2  18  16  − 40  147  80  − 102  2007 August 18  38.22  15.17  12.0  4.5  347  34  − 120  201  61  − 71  2007 October 21  42.38  12.97  10.0  4.2  330  31  − 44  100  69  − 113  2008 March 01  44.06  11.25  10.0  4.7  278  36  − 123  136  60  − 68  2008 March 01  44.35  11.49  10.0  4.0  318  32  − 108  160  60  − 79  2008 March 01  44.06  11.22  5.0  4.2  326  43  − 67  116  51  − 110  2008 April 08  39.16  16.66  10.0  4.4  235  49  − 35  350  64  − 134  2008 October 24  44.34  7.36  10.0  4.1  308  51  − 150  198  67  − 43  2009 March 30  42.33  13.36  11.0  4.4  2  35  − 70  158  57  − 104  2009 April 05  42.36  13.37  10.0  4.2  147  37  − 108  349  55  − 77  2009 April 06  42.33  13.33  10.0  6.3  326  35  − 80  134  56  − 97  2009 April 06  42.41  13.32  10.0  5.1  355  46  − 53  128  55  − 122  2009 April 06  42.38  13.34  10.0  4.5  340  25  − 103  175  66  − 84  2009 April 06  42.35  13.37  10.0  4.2  138  41  − 93  323  49  − 87  2009 April 06  42.36  13.33  10.0  4.4  348  40  − 64  135  55  − 111  2009 April 06  42.45  13.36  10.0  5.1  341  44  − 68  132  50  − 109  2009 April 07  42.34  13.39  10.0  5.1  341  41  − 64  128  54  − 111  2009 April 07  42.28  13.46  15.0  5.5  105  53  − 134  342  55  − 48  2009 April 07  42.38  13.38  10.0  4.5  321  41  − 64  108  54  − 110  2009 April 08  42.30  13.43  10.0  4.0  344  38  − 84  156  52  − 95  2009 April 08  42.51  13.36  10.0  4.1  319  40  − 76  121  51  − 101  2009 April 09  42.48  13.34  15.0  5.4  329  45  − 81  136  46  − 99  2009 April 09  42.50  13.36  17.0  5.2  321  44  − 83  132  46  − 97  2009 April 09  42.44  13.42  10.0  4.3  113  57  − 144  2  61  − 39  2009 April 13  42.50  13.36  10.0  5.0  337  38  − 71  133  54  − 104  2009 April 14  42.53  13.28  10.0  4.0  309  42  − 92  132  48  − 88  2009 April 15  42.54  13.28  10.0  4.1  113  33  − 126  333  64  − 69  2009 April 23  42.25  13.49  10.0  4.1  126  43  − 105  326  49  − 76  2009 April 23  42.23  13.48  10.0  4.3  323  27  − 95  149  63  − 87  2009 June 22  42.45  13.36  14.0  4.7  113  19  − 112  315  72  − 83  2009 July 03  42.41  13.39  10.0  4.1  144  42  − 108  348  50  − 74  2009 July 12  42.34  13.38  10.0  4.3  342  35  − 76  146  56  − 99  2009 September 24  42.45  13.33  10.0  4.2  184  35  − 76  347  56  − 100  2009 November 08  37.83  14.55  15.0  4.5  310  21  − 54  92  73  − 102  2010 April 15  43.49  12.44  2.0  4.1  144  21  − 57  288  72  − 102  2010 June 16  38.83  16.14  15.0  4.1  109  50  − 38  225  62  − 133  2010 August 28  42.85  12.66  15.0  4.1  159  44  − 113  9  50  − 70  2010 September 17  41.49  15.63  30.1  4.3  148  45  − 25  256  73  − 132  2011 April 24  35.82  14.88  20.3  4.2  28  34  − 76  191  57  − 99  2011 May 24  43.86  12.03  5.0  4.2  266  52  − 132  142  54  − 49  2011 June 23  38.06  14.76  7.4  4.7  59  44  − 130  289  58  − 58  2011 July 06  38.01  14.80  7.5  4.1  115  44  − 53  249  56  − 120  2011 July 12  43.92  11.86  7.8  4.3  103  34  − 114  311  59  − 74  2011 July 12  43.92  11.85  7.4  4.2  109  37  − 102  304  54  − 81  2011 July 12  43.93  11.86  15.0  4.0  126  26  − 86  301  64  − 92  2011 July 25  44.98  7.28  25.1  4.7  264  28  − 60  50  66  − 105  2012 March 05  44.54  9.38  10.5  4.3  297  19  − 114  143  73  − 82  2012 March 15  42.81  13.20  6.0  4.0  297  36  − 99  128  54  − 83  2012 April 13  38.19  13.31  20.0  4.5  273  43  − 120  131  54  − 65  2012 May 28  39.86  16.12  3.0  4.5  137  31  − 119  350  63  − 74  2012 October 03  44.57  7.21  10.0  4.0  161  35  − 88  338  55  − 92  2012 October 25  39.88  16.01  15.0  5.3  162  40  − 84  334  50  − 95  2013 January 04  37.81  14.80  10.0  4.4  297  32  − 70  94  60  − 102  2013 February 16  41.71  13.58  11.0  4.9  309  47  − 118  168  50  − 63  2013 June 21  44.15  10.14  5.1  5.4  247  32  − 141  123  71  − 64  2013 June 21  44.16  10.15  10.0  4.3  325  49  − 54  97  52  − 124  2013 June 23  44.18  10.21  9.5  4.7  249  35  − 132  117  65  − 65  2013 June 30  44.17  10.20  9.8  4.8  281  21  − 91  102  69  − 90  2013 December 18  43.38  12.53  15.0  4.2  316  21  − 80  125  69  − 94  2013 December 22  43.38  12.52  10.0  4.3  158  22  − 54  301  73  − 103  2013 December 29  41.37  14.44  15.0  5.2  109  46  − 123  332  53  − 61  2014 January 20  41.36  14.45  11.0  4.4  137  29  − 65  289  64  − 103  2014 June 06  39.90  16.09  10.0  4.3  178  26  − 48  313  71  − 108  2014 April 07  44.47  6.69  5.0  4.9  29  40  − 68  181  54  − 107  2014 September 07  44.11  10.66  12.0  4.4  130  31  − 139  3  70  − 66  2014 December 28  39.29  16.36  11.0  4.5  14  40  − 84  186  50  − 95  2015 February 28  41.98  13.53  17.0  4.4  326  39  − 73  125  53  − 103  2015 August 03  39.16  16.53  26.0  4.2  255  49  − 46  20  57  − 128  View Large Table 2. List of 128 earthquakes selected as input data and classified as thrust faulting focal mechanisms (TF, blue lower hemisphere focal mechanisms in Fig. 2). Date  Lat (°)  Lon (°)  Depth (km)  Mw  Strike1 (°)  Dip1 (°)  Rake1 (°)  Strike2 (°)  Dip2 (°)  Rake2 (°)  1967 December 30  44.63  12.01  33.0  5.2  322  56  84  152  34  98  1968 January 15  37.75  12.98  10.0  5.4  156  64  134  270  50  35  1976 May 06  46.36  13.27  11.7  6.4  282  23  119  71  70  78  1976 May 07  46.25  13.30  25.6  4.9  95  37  63  307  58  108  1976 May 09  46.26  13.36  19.7  5.1  89  48  60  310  50  119  1976 May 11  46.31  13.00  13.3  5.0  283  35  123  65  61  69  1976 September 11  46.33  13.20  9.6  5.3  271  38  116  60  56  71  1976 September 11  46.34  13.20  23.9  5.6  260  24  91  79  66  90  1976 September 15  46.32  13.20  1.9  5.9  246  36  84  73  54  94  1976 September 15  46.32  13.17  12.0  6.0  272  29  115  64  64  77  1977 September 16  46.33  13.00  12.0  5.2  291  35  119  77  60  72  1979 January 20  38.67  12.86  9.0  4.9  72  29  53  293  67  109  1979 December 08  38.28  11.74  33.0  5.3  235  45  67  87  50  111  1980 January 05  45.03  7.46  12.0  4.8  300  48  31  187  67  133  1980 May 28  38.48  14.25  14.0  5.7  83  43  99  252  48  82  1980 June 01  38.39  14.33  10.0  4.8  65  39  91  243  51  89  1981 February 14  41.05  14.60  10.0  4.9  254  46  157  1  73  46  1981 June 07  37.67  12.47  18.0  4.9  48  29  48  274  69  110  1981 June 22  38.49  14.09  13.0  4.8  71  47  116  215  49  65  1983 November 09  44.69  10.32  37.0  5.0  14  43  29  262  71  129  1986 January 08  42.59  15.31  27.0  4.7  312  43  95  125  47  86  1986 January 26  42.63  15.33  10.0  4.3  311  33  108  110  58  78  1986 August 29  46.34  12.47  10.0  4.7  219  47  62  77  50  117  1987 July 03  43.25  13.94  12.0  5.1  107  53  44  347  56  134  1988 April 26  42.37  16.57  24.0  5.4  289  44  121  68  53  63  1988 April 26  42.21  16.48  15.0  4.4  105  28  105  268  63  82  1990 February 01  42.20  15.57  10.0  4.4  227  29  66  74  64  103  1992 July 16  42.43  14.30  5.0  4.2  89  29  138  218  71  68  1995 September 30  41.90  15.97  10.0  5.2  197  32  58  53  64  108  1996 October 15  44.79  10.78  10.0  5.4  217  53  47  94  54  132  1996 October 15  44.78  10.73  10.0  4.4  275  45  139  36  63  53  1998 January 17  38.40  12.90  10.0  4.8  58  29  71  260  62  100  1998 May 06  46.24  13.71  10.0  4.3  247  44  40  127  64  127  1998 June 20  38.46  13.08  10.0  5.2  69  22  76  264  68  96  1998 June 21  38.50  13.10  10.0  4.6  69  36  77  265  55  99  1998 June 21  38.43  12.67  10.0  4.6  88  38  102  252  53  80  1998 September 14  38.46  13.60  10.0  5.0  72  30  80  263  60  96  1999 December 30  38.29  11.85  10.0  4.8  50  33  82  240  57  95  2000 April 26  40.98  10.10  10.0  4.8  179  39  83  8  51  96  2000 May 02  44.24  12.02  10.0  4.2  304  41  81  136  50  98  2000 May 06  44.14  11.97  10.0  4.1  287  33  64  137  61  106  2000 May 08  44.30  11.90  10.0  4.6  326  33  85  152  57  93  2000 May 09  44.20  12.00  10.0  4.3  308  31  96  121  59  87  2000 May 10  44.30  11.90  10.0  4.8  309  43  97  120  47  84  2000 May 11  44.34  11.91  10.0  4.2  303  46  117  86  50  64  2000 May 12  44.35  11.95  10.0  4.4  282  43  85  108  47  94  2000 June 27  40.95  10.03  10.0  4.3  184  27  82  13  64  94  2000 August 01  43.98  12.34  10.0  4.3  212  28  42  84  72  112  2000 September 02  43.26  12.99  33.0  4.4  325  40  82  156  51  97  2001 February 25  43.46  7.47  8.0  4.5  229  37  60  85  59  111  2001 May 26  37.46  16.34  33.0  4.5  71  54  134  192  55  46  2001 November 07  41.30  10.20  10.0  4.5  334  29  77  169  62  97  2002 April 05  38.48  14.74  10.0  4.4  90  41  108  246  52  75  2002 June 08  44.34  10.64  10.0  4.2  301  45  116  86  51  66  2002 June 18  44.44  10.80  33.0  4.3  293  44  103  95  48  78  2002 September 06  38.38  13.70  5.0  5.8  37  42  64  251  53  112  2002 September 06  38.44  13.73  4.0  4.7  252  48  126  24  53  56  2002 September 10  38.47  13.70  5.0  4.4  71  29  126  211  67  72  2002 September 20  38.46  13.74  5.0  4.7  46  33  77  241  58  99  2002 September 27  38.44  13.69  5.0  5.1  39  38  68  246  56  106  2002 September 28  38.47  13.71  5.0  4.6  79  39  103  243  52  80  2002 October 02  38.46  13.72  5.0  4.9  33  41  59  252  56  115  2002 October 23  42.61  17.16  16.0  4.3  103  43  69  311  50  108  2003 March 27  43.15  15.34  10.0  4.9  133  44  128  266  57  59  2003 March 29  43.11  15.46  10.0  5.5  287  41  85  114  49  95  2003 March 30  43.17  15.43  10.0  4.2  99  41  101  264  50  80  2003 March 30  43.17  15.53  10.0  4.6  98  43  83  287  47  96  2003 March 31  43.13  15.47  10.0  4.5  290  43  97  101  48  84  2003 April 03  43.15  15.43  10.0  4.3  105  25  116  256  67  78  2003 April 26  43.16  15.26  10.0  4.4  118  48  114  264  48  66  2003 April 29  43.25  15.57  10.0  4.4  109  32  61  322  63  107  2003 May 05  43.22  15.51  10.0  4.1  105  52  40  348  60  134  2003 June 21  43.07  15.31  10.0  4.4  249  40  62  103  56  111  2003 September 14  44.24  11.42  20.0  5.3  246  40  68  94  53  107  2003 December 07  44.16  12.18  9.0  4.2  284  45  71  130  48  108  2004 July 12  46.34  13.63  10.0  5.2  117  54  138  235  57  45  2004 November 24  45.63  10.56  17.0  5.0  235  25  92  53  65  89  2004 November 25  43.17  15.36  21.0  5.3  111  41  99  280  49  82  2004 December 03  43.09  15.50  10.0  4.6  279  32  91  97  58  89  2004 December 18  40.89  10.15  10.0  4.6  144  49  51  15  54  126  2006 April 16  44.02  11.81  10.0  4.5  295  34  91  114  56  89  2006 May 29  41.80  15.90  31.0  4.6  260  39  112  53  55  73  2006 June 22  39.73  16.60  15.0  4.7  173  44  100  339  47  80  2006 September 07  40.57  16.19  34.0  4.1  178  55  35  66  62  139  2006 December 10  41.94  16.20  35.0  4.5  28  31  83  217  59  94  2007 May 09  44.80  10.52  20.0  4.2  258  45  63  115  51  115  2008 February 21  37.82  17.97  30.0  4.7  333  27  134  106  71  71  2008 December 23  44.56  10.41  28.0  5.5  295  34  97  107  56  86  2008 December 23  44.52  10.39  31.0  4.9  286  34  84  113  57  94  2009 April 05  44.24  12.00  28.0  4.8  244  41  44  118  63  122  2009 September 07  38.59  14.04  10.0  4.8  276  41  124  54  57  64  2009 October 19  44.88  9.79  20.0  4.1  41  43  59  260  54  115  2010 June 04  42.37  16.59  15.0  4.3  61  48  62  279  49  117  2010 September 05  44.11  12.17  15.0  4.0  200  43  125  336  56  62  2011 July 07  42.06  7.60  10.0  5.1  43  39  93  219  51  87  2011 July 17  45.01  11.41  8.1  4.8  66  26  47  292  71  108  2011 October 20  44.53  9.41  10.0  4.2  278  34  62  131  60  108  2011 October 29  45.71  10.92  15.0  4.1  101  44  125  237  55  61  2012 March 04  42.03  7.63  2.0  4.5  35  33  84  222  57  94  2012 May 19  44.90  11.26  15.0  4.3  85  32  50  310  66  112  2012 May 20  44.89  11.25  10.0  6.1  109  30  99  279  60  85  2012 May 20  44.86  11.15  10.0  5.1  103  27  89  284  63  91  2012 May 20  44.83  11.49  15.0  5.2  100  37  64  312  57  109  2012 May 20  44.88  11.38  15.0  4.5  235  43  72  79  50  106  2012 May 21  44.85  11.35  15.0  4.1  243  37  92  60  53  89  2012 May 23  44.87  11.25  10.0  4.1  77  43  63  292  52  113  2012 May 29  44.85  11.09  15.0  6.0  110  20  103  276  71  85  2012 May 29  44.90  10.94  15.0  4.7  105  21  94  281  69  88  2012 May 29  44.89  11.01  6.8  5.5  112  32  101  279  59  83  2012 May 29  44.84  10.95  10.0  5.2  280  39  81  111  51  97  2012 June 03  44.90  10.94  15.0  4.9  92  16  37  326  81  103  2012 June 06  44.43  12.35  25.6  4.2  35  46  36  278  65  130  2012 June 09  46.21  12.44  7.1  4.2  240  31  88  62  59  91  2012 June 12  44.88  10.89  15.0  4.2  56  52  39  299  60  135  2012 August 13  38.52  13.73  26.5  4.2  19  24  63  229  69  102  2013 June 13  43.58  13.87  6.0  4.1  161  27  117  311  66  77  2013 July 21  43.53  13.74  10.0  5.2  109  41  56  331  57  116  2013 July 21  43.51  13.73  10.0  4.2  144  39  126  281  59  64  2013 August 22  43.58  13.69  10.0  4.5  144  30  93  321  60  89  2013 November 21  44.91  9.00  10.0  4.0  86  27  44  315  72  110  2013 December 15  36.67  14.94  15.0  4.1  83  47  143  200  63  49  2014 October 09  38.46  14.84  4.0  4.1  87  35  91  265  55  89  2014 August 28  45.67  10.70  10.0  4.0  72  45  123  209  54  61  2014 December 24  41.70  14.96  17.6  4.2  90  48  138  210  60  50  2015 May 29  42.92  14.30  10.0  4.5  338  41  108  135  51  75  2015 December 06  42.62  15.17  18.0  4.4  33  45  98  201  46  82  2015 December 06  42.45  15.30  5.0  4.6  229  34  120  15  61  72  2015 December 20  38.35  13.58  5.0  4.4  29  19  68  232  72  97  Date  Lat (°)  Lon (°)  Depth (km)  Mw  Strike1 (°)  Dip1 (°)  Rake1 (°)  Strike2 (°)  Dip2 (°)  Rake2 (°)  1967 December 30  44.63  12.01  33.0  5.2  322  56  84  152  34  98  1968 January 15  37.75  12.98  10.0  5.4  156  64  134  270  50  35  1976 May 06  46.36  13.27  11.7  6.4  282  23  119  71  70  78  1976 May 07  46.25  13.30  25.6  4.9  95  37  63  307  58  108  1976 May 09  46.26  13.36  19.7  5.1  89  48  60  310  50  119  1976 May 11  46.31  13.00  13.3  5.0  283  35  123  65  61  69  1976 September 11  46.33  13.20  9.6  5.3  271  38  116  60  56  71  1976 September 11  46.34  13.20  23.9  5.6  260  24  91  79  66  90  1976 September 15  46.32  13.20  1.9  5.9  246  36  84  73  54  94  1976 September 15  46.32  13.17  12.0  6.0  272  29  115  64  64  77  1977 September 16  46.33  13.00  12.0  5.2  291  35  119  77  60  72  1979 January 20  38.67  12.86  9.0  4.9  72  29  53  293  67  109  1979 December 08  38.28  11.74  33.0  5.3  235  45  67  87  50  111  1980 January 05  45.03  7.46  12.0  4.8  300  48  31  187  67  133  1980 May 28  38.48  14.25  14.0  5.7  83  43  99  252  48  82  1980 June 01  38.39  14.33  10.0  4.8  65  39  91  243  51  89  1981 February 14  41.05  14.60  10.0  4.9  254  46  157  1  73  46  1981 June 07  37.67  12.47  18.0  4.9  48  29  48  274  69  110  1981 June 22  38.49  14.09  13.0  4.8  71  47  116  215  49  65  1983 November 09  44.69  10.32  37.0  5.0  14  43  29  262  71  129  1986 January 08  42.59  15.31  27.0  4.7  312  43  95  125  47  86  1986 January 26  42.63  15.33  10.0  4.3  311  33  108  110  58  78  1986 August 29  46.34  12.47  10.0  4.7  219  47  62  77  50  117  1987 July 03  43.25  13.94  12.0  5.1  107  53  44  347  56  134  1988 April 26  42.37  16.57  24.0  5.4  289  44  121  68  53  63  1988 April 26  42.21  16.48  15.0  4.4  105  28  105  268  63  82  1990 February 01  42.20  15.57  10.0  4.4  227  29  66  74  64  103  1992 July 16  42.43  14.30  5.0  4.2  89  29  138  218  71  68  1995 September 30  41.90  15.97  10.0  5.2  197  32  58  53  64  108  1996 October 15  44.79  10.78  10.0  5.4  217  53  47  94  54  132  1996 October 15  44.78  10.73  10.0  4.4  275  45  139  36  63  53  1998 January 17  38.40  12.90  10.0  4.8  58  29  71  260  62  100  1998 May 06  46.24  13.71  10.0  4.3  247  44  40  127  64  127  1998 June 20  38.46  13.08  10.0  5.2  69  22  76  264  68  96  1998 June 21  38.50  13.10  10.0  4.6  69  36  77  265  55  99  1998 June 21  38.43  12.67  10.0  4.6  88  38  102  252  53  80  1998 September 14  38.46  13.60  10.0  5.0  72  30  80  263  60  96  1999 December 30  38.29  11.85  10.0  4.8  50  33  82  240  57  95  2000 April 26  40.98  10.10  10.0  4.8  179  39  83  8  51  96  2000 May 02  44.24  12.02  10.0  4.2  304  41  81  136  50  98  2000 May 06  44.14  11.97  10.0  4.1  287  33  64  137  61  106  2000 May 08  44.30  11.90  10.0  4.6  326  33  85  152  57  93  2000 May 09  44.20  12.00  10.0  4.3  308  31  96  121  59  87  2000 May 10  44.30  11.90  10.0  4.8  309  43  97  120  47  84  2000 May 11  44.34  11.91  10.0  4.2  303  46  117  86  50  64  2000 May 12  44.35  11.95  10.0  4.4  282  43  85  108  47  94  2000 June 27  40.95  10.03  10.0  4.3  184  27  82  13  64  94  2000 August 01  43.98  12.34  10.0  4.3  212  28  42  84  72  112  2000 September 02  43.26  12.99  33.0  4.4  325  40  82  156  51  97  2001 February 25  43.46  7.47  8.0  4.5  229  37  60  85  59  111  2001 May 26  37.46  16.34  33.0  4.5  71  54  134  192  55  46  2001 November 07  41.30  10.20  10.0  4.5  334  29  77  169  62  97  2002 April 05  38.48  14.74  10.0  4.4  90  41  108  246  52  75  2002 June 08  44.34  10.64  10.0  4.2  301  45  116  86  51  66  2002 June 18  44.44  10.80  33.0  4.3  293  44  103  95  48  78  2002 September 06  38.38  13.70  5.0  5.8  37  42  64  251  53  112  2002 September 06  38.44  13.73  4.0  4.7  252  48  126  24  53  56  2002 September 10  38.47  13.70  5.0  4.4  71  29  126  211  67  72  2002 September 20  38.46  13.74  5.0  4.7  46  33  77  241  58  99  2002 September 27  38.44  13.69  5.0  5.1  39  38  68  246  56  106  2002 September 28  38.47  13.71  5.0  4.6  79  39  103  243  52  80  2002 October 02  38.46  13.72  5.0  4.9  33  41  59  252  56  115  2002 October 23  42.61  17.16  16.0  4.3  103  43  69  311  50  108  2003 March 27  43.15  15.34  10.0  4.9  133  44  128  266  57  59  2003 March 29  43.11  15.46  10.0  5.5  287  41  85  114  49  95  2003 March 30  43.17  15.43  10.0  4.2  99  41  101  264  50  80  2003 March 30  43.17  15.53  10.0  4.6  98  43  83  287  47  96  2003 March 31  43.13  15.47  10.0  4.5  290  43  97  101  48  84  2003 April 03  43.15  15.43  10.0  4.3  105  25  116  256  67  78  2003 April 26  43.16  15.26  10.0  4.4  118  48  114  264  48  66  2003 April 29  43.25  15.57  10.0  4.4  109  32  61  322  63  107  2003 May 05  43.22  15.51  10.0  4.1  105  52  40  348  60  134  2003 June 21  43.07  15.31  10.0  4.4  249  40  62  103  56  111  2003 September 14  44.24  11.42  20.0  5.3  246  40  68  94  53  107  2003 December 07  44.16  12.18  9.0  4.2  284  45  71  130  48  108  2004 July 12  46.34  13.63  10.0  5.2  117  54  138  235  57  45  2004 November 24  45.63  10.56  17.0  5.0  235  25  92  53  65  89  2004 November 25  43.17  15.36  21.0  5.3  111  41  99  280  49  82  2004 December 03  43.09  15.50  10.0  4.6  279  32  91  97  58  89  2004 December 18  40.89  10.15  10.0  4.6  144  49  51  15  54  126  2006 April 16  44.02  11.81  10.0  4.5  295  34  91  114  56  89  2006 May 29  41.80  15.90  31.0  4.6  260  39  112  53  55  73  2006 June 22  39.73  16.60  15.0  4.7  173  44  100  339  47  80  2006 September 07  40.57  16.19  34.0  4.1  178  55  35  66  62  139  2006 December 10  41.94  16.20  35.0  4.5  28  31  83  217  59  94  2007 May 09  44.80  10.52  20.0  4.2  258  45  63  115  51  115  2008 February 21  37.82  17.97  30.0  4.7  333  27  134  106  71  71  2008 December 23  44.56  10.41  28.0  5.5  295  34  97  107  56  86  2008 December 23  44.52  10.39  31.0  4.9  286  34  84  113  57  94  2009 April 05  44.24  12.00  28.0  4.8  244  41  44  118  63  122  2009 September 07  38.59  14.04  10.0  4.8  276  41  124  54  57  64  2009 October 19  44.88  9.79  20.0  4.1  41  43  59  260  54  115  2010 June 04  42.37  16.59  15.0  4.3  61  48  62  279  49  117  2010 September 05  44.11  12.17  15.0  4.0  200  43  125  336  56  62  2011 July 07  42.06  7.60  10.0  5.1  43  39  93  219  51  87  2011 July 17  45.01  11.41  8.1  4.8  66  26  47  292  71  108  2011 October 20  44.53  9.41  10.0  4.2  278  34  62  131  60  108  2011 October 29  45.71  10.92  15.0  4.1  101  44  125  237  55  61  2012 March 04  42.03  7.63  2.0  4.5  35  33  84  222  57  94  2012 May 19  44.90  11.26  15.0  4.3  85  32  50  310  66  112  2012 May 20  44.89  11.25  10.0  6.1  109  30  99  279  60  85  2012 May 20  44.86  11.15  10.0  5.1  103  27  89  284  63  91  2012 May 20  44.83  11.49  15.0  5.2  100  37  64  312  57  109  2012 May 20  44.88  11.38  15.0  4.5  235  43  72  79  50  106  2012 May 21  44.85  11.35  15.0  4.1  243  37  92  60  53  89  2012 May 23  44.87  11.25  10.0  4.1  77  43  63  292  52  113  2012 May 29  44.85  11.09  15.0  6.0  110  20  103  276  71  85  2012 May 29  44.90  10.94  15.0  4.7  105  21  94  281  69  88  2012 May 29  44.89  11.01  6.8  5.5  112  32  101  279  59  83  2012 May 29  44.84  10.95  10.0  5.2  280  39  81  111  51  97  2012 June 03  44.90  10.94  15.0  4.9  92  16  37  326  81  103  2012 June 06  44.43  12.35  25.6  4.2  35  46  36  278  65  130  2012 June 09  46.21  12.44  7.1  4.2  240  31  88  62  59  91  2012 June 12  44.88  10.89  15.0  4.2  56  52  39  299  60  135  2012 August 13  38.52  13.73  26.5  4.2  19  24  63  229  69  102  2013 June 13  43.58  13.87  6.0  4.1  161  27  117  311  66  77  2013 July 21  43.53  13.74  10.0  5.2  109  41  56  331  57  116  2013 July 21  43.51  13.73  10.0  4.2  144  39  126  281  59  64  2013 August 22  43.58  13.69  10.0  4.5  144  30  93  321  60  89  2013 November 21  44.91  9.00  10.0  4.0  86  27  44  315  72  110  2013 December 15  36.67  14.94  15.0  4.1  83  47  143  200  63  49  2014 October 09  38.46  14.84  4.0  4.1  87  35  91  265  55  89  2014 August 28  45.67  10.70  10.0  4.0  72  45  123  209  54  61  2014 December 24  41.70  14.96  17.6  4.2  90  48  138  210  60  50  2015 May 29  42.92  14.30  10.0  4.5  338  41  108  135  51  75  2015 December 06  42.62  15.17  18.0  4.4  33  45  98  201  46  82  2015 December 06  42.45  15.30  5.0  4.6  229  34  120  15  61  72  2015 December 20  38.35  13.58  5.0  4.4  29  19  68  232  72  97  View Large Table 3. List of 85 earthquakes selected as input data and classified as strike-slip faulting focal mechanisms (SS, green lower hemisphere focal mechanisms in Fig. 2). Date  Lat (°)  Lon (°)  Depth (km)  Mw  Strike1 (°)  Dip1 (°)  Rake1 (°)  Strike2 (°)  Dip2 (°)  Rake2 (°)  1951 May 15  45.33  9.33  6.0  5.0  235  73  − 171  142  81  − 17  1951 May 16  45.33  9.33  6.0  4.5  123  64  − 17  220  74  − 152  1967 October 31  37.84  14.60  38.0  5.0  9  62  − 169  273  80  − 28  1970 August 19  43.25  10.77  33.0  4.7  35  57  − 156  291  70  − 35  1971 May 06  41.20  15.24  33.0  4.8  252  85  174  161  85  5  1971 November 29  40.34  15.77  4.0  4.7  23  84  6  292  84  173  1975 June 19  41.65  15.73  18.0  4.9  281  71  168  14  78  19  1975 November 16  44.75  9.52  20.0  4.8  312  62  − 32  58  62  − 147  1978 April 15  38.39  15.07  14.0  6.0  135  60  − 176  43  86  − 30  1979 April 18  46.36  13.28  10.0  4.7  323  66  169  58  80  24  1980 December 23  44.71  9.94  10.0  4.6  35  61  − 20  135  72  − 149  1981 February 14  41.05  14.60  10.0  4.9  254  46  157  1  73  46  1987 May 02  44.82  10.72  10.0  4.7  45  73  8  312  83  163  1989 September 13  45.80  11.21  10.0  4.9  56  89  0  146  90  − 179  1989 December 22  43.06  12.76  33.0  4.6  185  47  12  87  81  136  1990 May 05  40.75  15.85  26.0  5.8  184  73  13  90  78  162  1990 May 05  40.75  15.81  15.0  4.8  282  83  173  13  83  7  1990 October 29  36.23  14.67  23.0  4.8  198  72  − 13  292  78  − 161  1990 December 13  37.32  15.25  10.0  5.6  274  64  174  7  85  26  1991 February 11  44.87  6.70  14.0  4.5  224  76  − 11  316  79  − 166  1991 May 26  40.73  15.77  8.0  5.1  183  71  − 9  276  81  − 160  1993 June 26  37.92  14.21  10.0  4.8  170  53  6  76  85  143  1995 May 29  37.90  12.07  11.0  4.8  82  70  − 180  351  90  − 20  1995 October 10  44.18  10.01  10.0  4.8  89  68  178  180  88  22  1995 December 31  44.47  10.65  27.0  4.0  144  70  − 174  52  84  − 20  1997 March 25  36.93  16.03  33.0  4.5  104  78  179  194  89  12  1997 October 16  43.04  12.89  10.0  4.3  287  80  175  18  85  10  1998 April 12  46.24  13.65  10.0  5.6  218  67  − 4  309  87  − 157  1999 January 25  44.02  11.92  33.0  4.4  91  66  17  354  75  155  2000 June 18  44.76  10.73  5.0  4.4  308  68  − 161  210  73  − 23  2001 April 22  37.72  15.10  10.0  4.2  316  56  27  210  68  143  2001 July 17  46.70  11.30  10.0  4.8  210  72  7  117  83  162  2001 July 18  44.84  8.40  10.0  4.1  95  49  179  185  89  41  2002 October 27  37.79  15.16  10.0  4.9  320  60  171  55  82  30  2002 October 27  37.92  15.18  10.0  4.5  67  54  19  326  75  142  2002 October 29  37.67  15.27  10.0  4.7  316  61  − 173  223  84  − 29  2002 October 29  37.69  15.56  10.0  4.2  207  54  − 28  314  68  − 141  2002 October 31  41.79  14.87  10.0  5.7  174  67  − 8  267  82  − 157  2002 November 01  41.73  14.88  10.0  5.7  170  75  − 4  261  86  − 165  2002 November 01  41.87  14.83  10.0  4.5  263  56  − 166  165  78  − 35  2002 November 12  41.66  14.77  10.0  4.6  72  80  171  163  82  10  2003 April 11  44.79  8.89  4.0  4.8  297  75  − 165  203  75  − 16  2003 June 01  41.66  14.82  12.0  4.5  167  72  − 12  261  79  − 162  2003 July 07  36.01  14.90  10.0  4.3  350  62  4  258  87  152  2003 December 30  41.64  14.85  5.0  4.5  187  53  − 6  281  85  − 142  2005 August 22  41.47  12.53  10.0  4.8  341  62  180  71  90  28  2005 September 08  46.00  6.90  7.0  4.5  317  61  − 15  54  77  − 151  2006 April 10  43.40  13.49  33.0  4.1  89  71  − 169  355  80  − 20  2006 April 17  39.57  17.14  10.0  4.7  223  83  177  314  87  7  2006 October 04  42.07  15.75  36.0  4.3  274  79  178  4  89  11  2006 October 21  43.65  13.00  36.0  4.2  34  60  12  298  80  150  2006 November 23  35.97  12.94  10.0  4.8  357  70  − 2  88  88  − 160  2006 November 24  36.26  15.76  11.0  4.4  188  82  0  98  90  172  2008 March 19  41.91  15.85  28.0  4.2  69  57  145  179  61  38  2008 November 20  39.14  17.49  15.0  4.5  166  82  − 2  256  88  − 172  2008 November 28  37.54  13.69  35.0  4.4  337  74  9  245  81  164  2009 March 19  36.52  12.72  28.0  4.4  255  48  − 180  165  90  − 42  2009 April 09  42.34  13.44  18.0  4.4  67  50  − 170  331  83  − 40  2009 September 20  43.40  13.39  37.0  4.7  21  78  − 3  112  87  − 168  2009 December 15  43.01  12.28  15.0  4.2  163  75  2  72  88  165  2009 December 19  37.78  14.94  15.0  4.3  119  47  − 178  28  89  − 43  2010 January 12  43.26  13.47  31.0  4.1  52  48  − 161  309  76  − 44  2010 April 02  37.76  15.11  2.0  4.2  274  55  10  178  82  145  2010 August 16  38.36  14.95  10.0  4.7  221  73  − 6  312  85  − 163  2010 October 13  44.14  12.37  35.2  4.1  17  65  22  278  70  153  2010 October 15  38.87  16.66  15.0  4.4  287  62  173  20  84  28  2011 May 06  37.78  14.96  22.2  4.3  13  57  15  275  77  146  2011 November 15  38.26  14.67  15.0  4.2  7  63  − 6  99  85  − 152  2012 January 24  45.54  10.97  15.0  4.1  107  66  − 170  13  81  − 24  2012 Januray 25  44.85  10.54  33.0  5.0  335  46  − 16  76  79  − 135  2012 July 04  37.69  16.87  40.0  4.6  186  74  3  95  87  164  2012 August 12  41.77  16.27  8.4  4.1  267  55  149  16  65  39  2012 October 03  44.85  9.77  30.0  4.5  216  85  − 2  306  88  − 175  2012 November 22  37.80  14.96  10.0  4.1  258  65  154  359  66  28  2012 November 22  37.77  14.99  20.0  4.2  6  57  23  263  71  145  2013 January 25  44.17  10.45  15.0  5.0  246  68  − 167  151  78  − 22  2013 March 24  37.76  16.50  30.0  4.6  257  87  178  347  88  3  2014 January 14  38.37  14.92  12.0  4.1  315  78  171  46  81  12  2014 January 14  38.36  14.94  11.0  4.2  308  47  159  52  75  45  2014 December 19  43.61  11.26  10.0  4.3  257  50  − 166  157  79  − 40  2014 September 26  36.78  16.50  40.0  4.2  267  75  170  359  80  16  2014 December 19  43.60  11.25  10.0  4.2  345  78  − 9  76  81  − 168  2015 April 16  41.79  15.34  22.5  4.1  4  73  12  271  78  163  2015 August 08  38.55  14.26  14.0  4.0  350  77  4  259  86  167  2015 August 29  46.31  13.58  10.0  4.0  139  55  147  249  64  40  Date  Lat (°)  Lon (°)  Depth (km)  Mw  Strike1 (°)  Dip1 (°)  Rake1 (°)  Strike2 (°)  Dip2 (°)  Rake2 (°)  1951 May 15  45.33  9.33  6.0  5.0  235  73  − 171  142  81  − 17  1951 May 16  45.33  9.33  6.0  4.5  123  64  − 17  220  74  − 152  1967 October 31  37.84  14.60  38.0  5.0  9  62  − 169  273  80  − 28  1970 August 19  43.25  10.77  33.0  4.7  35  57  − 156  291  70  − 35  1971 May 06  41.20  15.24  33.0  4.8  252  85  174  161  85  5  1971 November 29  40.34  15.77  4.0  4.7  23  84  6  292  84  173  1975 June 19  41.65  15.73  18.0  4.9  281  71  168  14  78  19  1975 November 16  44.75  9.52  20.0  4.8  312  62  − 32  58  62  − 147  1978 April 15  38.39  15.07  14.0  6.0  135  60  − 176  43  86  − 30  1979 April 18  46.36  13.28  10.0  4.7  323  66  169  58  80  24  1980 December 23  44.71  9.94  10.0  4.6  35  61  − 20  135  72  − 149  1981 February 14  41.05  14.60  10.0  4.9  254  46  157  1  73  46  1987 May 02  44.82  10.72  10.0  4.7  45  73  8  312  83  163  1989 September 13  45.80  11.21  10.0  4.9  56  89  0  146  90  − 179  1989 December 22  43.06  12.76  33.0  4.6  185  47  12  87  81  136  1990 May 05  40.75  15.85  26.0  5.8  184  73  13  90  78  162  1990 May 05  40.75  15.81  15.0  4.8  282  83  173  13  83  7  1990 October 29  36.23  14.67  23.0  4.8  198  72  − 13  292  78  − 161  1990 December 13  37.32  15.25  10.0  5.6  274  64  174  7  85  26  1991 February 11  44.87  6.70  14.0  4.5  224  76  − 11  316  79  − 166  1991 May 26  40.73  15.77  8.0  5.1  183  71  − 9  276  81  − 160  1993 June 26  37.92  14.21  10.0  4.8  170  53  6  76  85  143  1995 May 29  37.90  12.07  11.0  4.8  82  70  − 180  351  90  − 20  1995 October 10  44.18  10.01  10.0  4.8  89  68  178  180  88  22  1995 December 31  44.47  10.65  27.0  4.0  144  70  − 174  52  84  − 20  1997 March 25  36.93  16.03  33.0  4.5  104  78  179  194  89  12  1997 October 16  43.04  12.89  10.0  4.3  287  80  175  18  85  10  1998 April 12  46.24  13.65  10.0  5.6  218  67  − 4  309  87  − 157  1999 January 25  44.02  11.92  33.0  4.4  91  66  17  354  75  155  2000 June 18  44.76  10.73  5.0  4.4  308  68  − 161  210  73  − 23  2001 April 22  37.72  15.10  10.0  4.2  316  56  27  210  68  143  2001 July 17  46.70  11.30  10.0  4.8  210  72  7  117  83  162  2001 July 18  44.84  8.40  10.0  4.1  95  49  179  185  89  41  2002 October 27  37.79  15.16  10.0  4.9  320  60  171  55  82  30  2002 October 27  37.92  15.18  10.0  4.5  67  54  19  326  75  142  2002 October 29  37.67  15.27  10.0  4.7  316  61  − 173  223  84  − 29  2002 October 29  37.69  15.56  10.0  4.2  207  54  − 28  314  68  − 141  2002 October 31  41.79  14.87  10.0  5.7  174  67  − 8  267  82  − 157  2002 November 01  41.73  14.88  10.0  5.7  170  75  − 4  261  86  − 165  2002 November 01  41.87  14.83  10.0  4.5  263  56  − 166  165  78  − 35  2002 November 12  41.66  14.77  10.0  4.6  72  80  171  163  82  10  2003 April 11  44.79  8.89  4.0  4.8  297  75  − 165  203  75  − 16  2003 June 01  41.66  14.82  12.0  4.5  167  72  − 12  261  79  − 162  2003 July 07  36.01  14.90  10.0  4.3  350  62  4  258  87  152  2003 December 30  41.64  14.85  5.0  4.5  187  53  − 6  281  85  − 142  2005 August 22  41.47  12.53  10.0  4.8  341  62  180  71  90  28  2005 September 08  46.00  6.90  7.0  4.5  317  61  − 15  54  77  − 151  2006 April 10  43.40  13.49  33.0  4.1  89  71  − 169  355  80  − 20  2006 April 17  39.57  17.14  10.0  4.7  223  83  177  314  87  7  2006 October 04  42.07  15.75  36.0  4.3  274  79  178  4  89  11  2006 October 21  43.65  13.00  36.0  4.2  34  60  12  298  80  150  2006 November 23  35.97  12.94  10.0  4.8  357  70  − 2  88  88  − 160  2006 November 24  36.26  15.76  11.0  4.4  188  82  0  98  90  172  2008 March 19  41.91  15.85  28.0  4.2  69  57  145  179  61  38  2008 November 20  39.14  17.49  15.0  4.5  166  82  − 2  256  88  − 172  2008 November 28  37.54  13.69  35.0  4.4  337  74  9  245  81  164  2009 March 19  36.52  12.72  28.0  4.4  255  48  − 180  165  90  − 42  2009 April 09  42.34  13.44  18.0  4.4  67  50  − 170  331  83  − 40  2009 September 20  43.40  13.39  37.0  4.7  21  78  − 3  112  87  − 168  2009 December 15  43.01  12.28  15.0  4.2  163  75  2  72  88  165  2009 December 19  37.78  14.94  15.0  4.3  119  47  − 178  28  89  − 43  2010 January 12  43.26  13.47  31.0  4.1  52  48  − 161  309  76  − 44  2010 April 02  37.76  15.11  2.0  4.2  274  55  10  178  82  145  2010 August 16  38.36  14.95  10.0  4.7  221  73  − 6  312  85  − 163  2010 October 13  44.14  12.37  35.2  4.1  17  65  22  278  70  153  2010 October 15  38.87  16.66  15.0  4.4  287  62  173  20  84  28  2011 May 06  37.78  14.96  22.2  4.3  13  57  15  275  77  146  2011 November 15  38.26  14.67  15.0  4.2  7  63  − 6  99  85  − 152  2012 January 24  45.54  10.97  15.0  4.1  107  66  − 170  13  81  − 24  2012 Januray 25  44.85  10.54  33.0  5.0  335  46  − 16  76  79  − 135  2012 July 04  37.69  16.87  40.0  4.6  186  74  3  95  87  164  2012 August 12  41.77  16.27  8.4  4.1  267  55  149  16  65  39  2012 October 03  44.85  9.77  30.0  4.5  216  85  − 2  306  88  − 175  2012 November 22  37.80  14.96  10.0  4.1  258  65  154  359  66  28  2012 November 22  37.77  14.99  20.0  4.2  6  57  23  263  71  145  2013 January 25  44.17  10.45  15.0  5.0  246  68  − 167  151  78  − 22  2013 March 24  37.76  16.50  30.0  4.6  257  87  178  347  88  3  2014 January 14  38.37  14.92  12.0  4.1  315  78  171  46  81  12  2014 January 14  38.36  14.94  11.0  4.2  308  47  159  52  75  45  2014 December 19  43.61  11.26  10.0  4.3  257  50  − 166  157  79  − 40  2014 September 26  36.78  16.50  40.0  4.2  267  75  170  359  80  16  2014 December 19  43.60  11.25  10.0  4.2  345  78  − 9  76  81  − 168  2015 April 16  41.79  15.34  22.5  4.1  4  73  12  271  78  163  2015 August 08  38.55  14.26  14.0  4.0  350  77  4  259  86  167  2015 August 29  46.31  13.58  10.0  4.0  139  55  147  249  64  40  View Large 3.2 Testing data The independent data set used to evaluate the reliability of the results consists of a set of earthquake focal mechanism solutions (http://cnt.rm.ingv.it/tdmt—2017 March 9) occurred within the Italian gridding zone (Fig. 1) during the year 2016 and characterized by the same boundary parameters of the input-data earthquakes, as magnitude ≥ 4 (except for only one Mw 3.9 earthquake) and hypocentral depth less than 40 km. We consider nine out-of-sample earthquakes (Fig. 1 and Table 4): Reggio Emilia (inner northern Apennine, Mw 4.0 December 9), Terni (central Apennine, Mw 4.1 May 30), Amatrice (central Apennine, Mw 6.0 August 24, Mw 5.9 October 26 and Mw 6.5 October 30), Firenze (Tuscany, Mw 3.9 October 25), Campobasso (Molise, Mw 4.3 January 16), Siracusa (Sicily, Mw 4.2 February 8) and Ionio (Ionian-Sea, Mw 4.0 March 6). Table 4. List of nine earthquakes focal mechanism s parameters (http://cnt.rm.ingv.it/) used as testing data shown in Fig. 1 (location) and Fig. 7 (black and white lower hemisphere focal mechanisms). Date  Location  Lat (°)  Lon (°)  Depth (km)  Mw  Strike1 (°)  Dip1 (°)  Rake1 (°)  Strike2 (°)  Dip2 (°)  Rake2 (°)  2016 January 16  e  41.5337  14.5995  6  4.3  305  49  102  143  43  77  2016 February 08  f  36.9765  14.8692  6  4.2  282  83  170  191  80  7  2016 March 06  g  38.1838  16.7505  39  4.0  248  75  158  344  69  16  2016 May 30  b  42.7115  11.9648  5  4.1  124  47  − 87  300  43  − 93  2016 August 24  c  42.7063  13.2232  5  6.0  155  49  − 87  331  41  − 93  2016 October 25  d  43.6007  10.994  9  3.9  260  89  158  350  68  1  2016 October 26  c  42.9152  13.1278  6  5.9  159  47  − 93  344  43  − 87  2016 October 30  c  42.8398  13.1102  5  6.5  151  47  − 89  330  43  − 91  2016 December 09  a  44.3298  10.5002  6  4.0  162  53  − 82  329  38  − 100  Date  Location  Lat (°)  Lon (°)  Depth (km)  Mw  Strike1 (°)  Dip1 (°)  Rake1 (°)  Strike2 (°)  Dip2 (°)  Rake2 (°)  2016 January 16  e  41.5337  14.5995  6  4.3  305  49  102  143  43  77  2016 February 08  f  36.9765  14.8692  6  4.2  282  83  170  191  80  7  2016 March 06  g  38.1838  16.7505  39  4.0  248  75  158  344  69  16  2016 May 30  b  42.7115  11.9648  5  4.1  124  47  − 87  300  43  − 93  2016 August 24  c  42.7063  13.2232  5  6.0  155  49  − 87  331  41  − 93  2016 October 25  d  43.6007  10.994  9  3.9  260  89  158  350  68  1  2016 October 26  c  42.9152  13.1278  6  5.9  159  47  − 93  344  43  − 87  2016 October 30  c  42.8398  13.1102  5  6.5  151  47  − 89  330  43  − 91  2016 December 09  a  44.3298  10.5002  6  4.0  162  53  − 82  329  38  − 100  View Large 3.3 The forecasting model Here, we describe the model that is used to forecast the focal mechanism and faulting style of the next moderate to large earthquakes in the Italian region. The model assumes that the stress field in Italy of the next decades will be the same of the past decades; hence, we combine the focal mechanism of the past seismicity to obtain an ‘average’ moment tensor for the next earthquakes. The methodology is inspired by the Cumulative Moment Tensor technique proposed by Kostrov (1974) and subsequently exploited by Selva & Marzocchi (2004). The Cumulative Moment Tensor describes the contribution of each earthquake to the average strain tensor ε within a rock volume V. This strain is proportional to the moment tensor $${{\cal M}_{ij}}$$, so that the average strain induced by earthquakes is given by   \begin{equation}{\varepsilon _{ij}} = \ \frac{1}{{2\mu V}}\mathop \sum \limits_{k = 1}^N {\cal M}_{ij}^{( {\boldsymbol{k}})}\end{equation} (1)where μ is the shear modulus, and the sum is taken for the N earthquakes located within the volume. Eq. (1) represents a basic equation of moment tensor summation method that defines seismic deformation for a defined small area. Selva & Marzocchi (2004) generalize the same concept introducing the Weighted Cumulative Moment Tensor (WCMT) that takes into account the distance of the information from a specific point, for instance, the centre of the cell of a grid. In this case, the cumulative seismic moment tensor for a generic kth cell is   \begin{equation} \widetilde {{{\cal M}_k}} = \ \frac{{\mathop \sum \nolimits_{l = 1}^{{N_k}} {{\cal M}_l} \cdot {\omega _{lk}}}}{{\mathop \sum \nolimits_{l = 1}^{{N_k}} {\omega _{lk}}}}\end{equation} (2)where $$\widetilde {{{\cal M}_k}}$$ is the average seismic moment tensor of the kth cell, $${{\cal M}_l}$$ is the seismic moment tensor of the lth earthquake at a distance Δlk from the centre of the kth cell and ωlk is   \begin{equation}{\omega _{lk}} = \ \frac{1}{{{\rm{\Delta }}_{lk}^2}}\end{equation} (3)Eq. (3) is applied only for a maximum distance R = 50 km. This threshold accounts for the geological and geodynamic complexity of Italy and the highly heterogeneous spatial distribution of the considered stress data. Previous papers on stress interpolation analysis (Pierdominici & Heidbach 2012; Carafa & Barba 2013) investigated extensively the problem to define a meaningful search radius in Italy, finding comparable R-values. From a practical point of view, by using this threshold, we exclude data too distant to be considered representative for the kth cell. Adopting the WCMT concept, we estimate the seismic moment tensor parameters for each one of 8993 cells (0.1° × 0.1° spaced) in which we have equally divided the study area (Fig. 2). In particular, we apply eq. (2) to calculate the average moment tensor for each possible faulting style α = {NF, TF, SS} where NF, TF and SS mean normal, reverse and strike-slip faulting, respectively. In other words, we average only the same faulting style information defining the Total Weighted Moment Tensor ($${\rm{TWMT}}_k^{( \alpha )}$$)   \begin{equation}{\rm{TWMT}}_k^{(\alpha)} = \widetilde{{\cal M}}_k^{( \alpha)} = \ \frac{{\mathop \sum \nolimits_{l = 1}^{N_k^{(\alpha)}} {\cal M}_l^{(\alpha)} \cdot {\omega _{lk}}}}{{\mathop \sum \nolimits_{l = 1}^{N_k^{(\alpha)}} {\omega _{lk}}}}\end{equation} (4)where $$N_k^{( \alpha )}$$ is the number of past earthquakes at a distance Δlk ≤ R from the kth each. The eigenvalues and eigenvectors of the tensor $${\rm{TWMT}}_k^{( \alpha )}$$ are the average $$T_k^{( \alpha )},\ P_k^{( \alpha )},\ B_k^{( \alpha )}$$, that is, they are the average orientations of T, P and B axes in the kth cell. Then, applying the Zoback (1992) criteria, we obtain the weighted azimuths of SHmax for each kth cell. The last step of the procedure is to compute the conditional probability of mechanism α given an earthquake is occurred in the kth cell. For this purpose, we define   \begin{equation}C_k^{(\alpha)} = \ \mathop \sum \limits_{l = 1}^{N_k^{(\alpha)}} {\omega _{lk}}\end{equation} (5)that provides the overall weight of the information related to the faulting type α. Hence, the conditional probability of the next focal mechanism α in the kth cell given the occurrence of an earthquake can be estimated by   \begin{equation}P_k^{(\alpha)} = \ \frac{{C_k^{(\alpha)}}}{{C_k^{\left( {{\rm{TOT}}} \right)}}}\end{equation} (6)where   \begin{equation}C_k^{\left( {{\rm{TOT}}} \right)} = \ C_k^{\left( {{\rm{NF}}} \right)} + C_k^{\left( {{\rm{TF}}} \right)} + C_k^{\left( {{\rm{SS}}} \right)}\end{equation} (7) The use of eq. (6) to estimate the conditional probability of the focal mechanism α in the kth cell requires some further discussion. This definition of probability satisfies the Kolmogorov axioms (Kolmogorov 1956) and it can be interpreted in the Bayesian perspective of bet quotient or degree of belief (e.g. Lindley 2000). Assuming that only one specific (unknown) focal mechanism is allowed in each cell of the grid for earthquakes of interest in PSHA, the probability of eq. (6) does not describe the expected frequency of focal mechanisms that are going to be observed in the cell, but it describes only the epistemic uncertainty through the subjective concept of bet quotient. For practical purpose, the user may consider all possibilities (to fully consider the epistemic uncertainty) or just take the most likely outcome. We also assign a sort of degree of accuracy of the results taking into account the value of $$C_k^{( {{\rm{TOT}}} )}$$ in eq. (7); de facto, this quantity gives a measure of how many earthquakes and their proximity to the cell have been considered to estimate the focal mechanisms. We define three classes based on the total contribution of weights in the cell of interest (eq. 7): (i) if $$C_k^{( {{\rm{TOT}}} )}$$ ≤ 33th percentile of the distribution of $$C_k^{( {{\rm{TOT}}} )}$$ for all cells, the kth cell belongs to ‘Class 1’; (ii) if $$C_k^{( {{\rm{TOT}}} )}$$ is comprised between 33th and 66th percentile the cell belongs to ‘Class 2’ and (iii) if $$C_k^{( {{\rm{TOT}}} )}$$ ≥ 66th percentile the cell belongs to ‘Class 3’. As final consideration, we remark that using eq. (6) we may get probability equal to 1 in some cell. Although here we do not deepen this problem, we strongly encourage practitioners to avoid using probabilities equal to 1. This can be easily done introducing a 'surprise' factor ε   \begin{equation}\widetilde {P_k^{(\alpha)}} = \ P_k^{(\alpha)} - \epsilon \end{equation} (8)and using $$\widetilde {P_k^{( \alpha )}}$$ instead of $$P_k^{( \alpha )}$$. The surprise factor is the probability that the next earthquake may have an unexpected focal mechanism; hence it may depend on the class of accuracy defined above. 4 RESULTS We compute separately the TWMT for each possible faulting style according to eq. (4). In Table S1–S3 (Supporting Information), we show all expected moment tensors and the probability of occurrence associated to different faulting styles, for each cell of the grid. In Fig. 3, we show the spatial distribution of the prevailing focal mechanisms represented by lower hemisphere focal mechanisms (NF in red, TF in blue and SS in green). The map shows all tectonic regimes with prevailing NF along the entire Apennines, reverse faulting along the outer areas and strike-slip located in specific areas, while in some regions, different styles of faulting coexist in close proximity with different focal mechanism orientations. Overall, the different style of faulting are distributed in about 33 per cent NF, 35 per cent TF and 32 per cent SS. Figure 3. View largeDownload slide The prevailing moment tensor computed in each cell shown as focal mechanism. The red, blue and green lower hemisphere focal mechanisms correspond to the weighted focal mechanisms obtained and classified as normal (NF), reverse (TF) and strike-slip (SS) faulting, respectively. Figure 3. View largeDownload slide The prevailing moment tensor computed in each cell shown as focal mechanism. The red, blue and green lower hemisphere focal mechanisms correspond to the weighted focal mechanisms obtained and classified as normal (NF), reverse (TF) and strike-slip (SS) faulting, respectively. In Fig. 4, we show for each cell the conditional probabilities of the different expected faulting styles, as from eqs (6) to (8). In particular, the computed conditional probabilities associated to the style of faulting are represented by a three slices pie chart representing the NF (red), TF (blue) and SS (green) probability of occurrence, for each cell. Figure 4. View largeDownload slide Pie charts resulting from the computation conditional probability for the next NF (red), TF (blue) and SS (green) events expected for each cell. Figure 4. View largeDownload slide Pie charts resulting from the computation conditional probability for the next NF (red), TF (blue) and SS (green) events expected for each cell. In Fig. 5, we show the SHmax forecasts, which describe well the tectonics complexity discussed in the previous section of the paper (cf. Section 2 and Fig. 1). Figure 5. View largeDownload slide SHmax orientation obtained for each cell after the TWMT and conditional probability computations. The orientations are coloured according to the tectonic regime (red, NF; green, SS and blue, TF). Figure 5. View largeDownload slide SHmax orientation obtained for each cell after the TWMT and conditional probability computations. The orientations are coloured according to the tectonic regime (red, NF; green, SS and blue, TF). In Fig. 6 (and for details Fig. S1, Supporting Information), we show the accuracy of the results according the three-classes scheme described before; in particular, results belonging to ‘Class 1’, ‘Class 2’ and ‘Class 3’ are represented in white, yellow and orange dots, respectively. Figure 6. View large Download slide Map of the accuracy classes based on the total contribution of weights in each cell (eq. 7): (i) if $$C_k^{( {{\rm{TOT}}} )}$$≤ 33th percentile of the distribution of $$C_k^{( {{\rm{TOT}}} )}$$ for all cells, the kth cell belongs to ‘Class 1’; (ii) if $$C_k^{( {{\rm{TOT}}} )}$$ is comprised between 33th and 66th percentile the cell belongs to ‘Class 2’ and (iii) if $$C_k^{( {{\rm{TOT}}} )}$$ ≥ 66th percentile the cell belongs to ‘Class 3’ (for statistical distribution details see Fig. S1, Supporting Information). Figure 6. View large Download slide Map of the accuracy classes based on the total contribution of weights in each cell (eq. 7): (i) if $$C_k^{( {{\rm{TOT}}} )}$$≤ 33th percentile of the distribution of $$C_k^{( {{\rm{TOT}}} )}$$ for all cells, the kth cell belongs to ‘Class 1’; (ii) if $$C_k^{( {{\rm{TOT}}} )}$$ is comprised between 33th and 66th percentile the cell belongs to ‘Class 2’ and (iii) if $$C_k^{( {{\rm{TOT}}} )}$$ ≥ 66th percentile the cell belongs to ‘Class 3’ (for statistical distribution details see Fig. S1, Supporting Information). It is worth stressing that, in general, the quality of the forecasts is unavoidably related to the number of input information. While it is obvious that the larger the number of data, the better, conversely it is not possible to identify the minimum number of information above which the forecasts can be considered reliable. The only way to evaluate the forecasts and to validate a model is through the comparison with independent data (e.g. Marzocchi & Jordan 2014); if the independent data set is limited, also a qualitative comparison between forecasts and the geological knowledge of the territory may increase the confidence on the quality of the forecasts. This is what we do in the next section. 5 DISCUSSION AND CONCLUSIONS In this paper, we provide spatial forecasts of the focal mechanism of the future moderate-large earthquake in a spatial grid 0.1°–0.1° that covers the whole Italian territory. One of the main applications of these forecasts is to contribute to reduce the epistemic uncertainty in PSHA. In fact, it has been proposed that earthquakes with the same magnitude and distance from a specific site induce different ground shaking as a function of the focal mechanism that characterize them (e.g. Campbell 1984; Bommer et al. 2003; Convertito & Herrero 2004; Convertito & Herrero 2006; Strasser et al. 2006; Roselli et al. 2016): on average, ground shaking caused by reverse earthquakes is larger than ground shaking caused by same magnitude and distance strike-slip earthquakes that, in turn, is larger than NF earthquakes (Campbell 1984; Strasser et al.2006). By using the TWMT, we map the results obtained for each cell along the entire Italian territory with different degrees of accuracy. The results allow us defining (i) the expected focal mechanism (Tables S1–S3, Supporting Information) and the faulting style, normal, reverse or strike-slip (Fig. 3); (ii) their probability of occurrence (Fig. 4); (iii) the SHmax orientation map (Fig. 5) as a function of the tectonic regimes. The forecasts of Figs 3–5 highlight some interesting features. Moving from north to south (Fig. 5 and subordinately Figs 3 and 4) and considering only the most likely focal mechanism solution for each cell, the results show that the Italian northern sector is characterized by a strong inhomogeneity mainly because of the presence of three different tectonic regimes (see Figs 3 and 5) and, only to a lesser extent because of the SHmax orientation. The latter (Fig. 5) looks uniform, N–S oriented, along the central and eastern part of this sector (Po Plain and Friuli area); the western part however is characterized by a not homogeneous SHmax both in tectonic regime and in orientation except for local areas (less than 100 km length). The Apennines—from Tuscany to Calabria region—show a wide distribution of NF mechanisms mainly aligned with the NW–SE Apennine belt. Only along the coastal Tyrrhenian areas beside to NF mechanisms, local strike-slip mechanisms are present with different SHmax orientations. Along the Adriatic side, the reverse faulting mechanisms characterize the most part of the Adriatic foredeep from the Po Plain up to Gargano area. Strike-slip mechanisms are also present but restricted to few zones. The SHmax orientations well depict the sectors with northward and NE compressions almost reaching the Dinarides. In the Calabria–Sicily region, the SHmax rotation following the natural curvature of the Calabrian arc is very well defined with NF mechanisms. The Sicilian Tyrrhenian zone is comparable with the previous Po Plain sector characterized by N-S compression and prevalent reverse faulting mechanisms. Finally, along the Ionian Sea relative to Calabria and Sicily regions is defined a narrow area characterized by SS mechanism and regular NW SHmax orientations. To verify the reliability of the forecasts, we carry out a qualitative evaluation of the forecasts comparing them with testing data, not previously used to calibrate the model. We use nine earthquakes with Mw ≥ 3.9 occurred during 2016 in seven different Italian regions (Fig. 1), whose focal mechanism solutions are relative to the Time Domain Moment Tensor Catalogue (http://cnt.rm.ingv.it/en/tdmt). In Fig. 7, we show the observed (black lower hemisphere focal mechanisms) and the forecast NF (red) TF (blue) and SS (green) focal solutions. Moreover, we associate to each of them, the corresponding pie chart in the centre of cells, where the slices show the percentage of probability of occurrence associated to NF (light red slices) TF (light blue slices) and SS (light green slices) expected stress regime. Below, we describe each specific testing earthquake. Reggio Emilia (Fig. 7a): The Mw 4.0 Reggio Emilia earthquake has a NF mechanism and occurred very close to the boundary where NF kinematics moves toward a compressional tectonics. In fact, the seismic event is located in the middle of a cell showing normal and compressive focal mechanisms with consistent orientation of nodal planes. Terni (Fig. 7b): The forecast for the area around Terni Mw 4.1 seismic event shows that the most likely mechanism is NF (≈70 per cent), with a lower probability for strike-slip mechanism (≈30 per cent). The mechanism of the observed seismic event is then in agreement with the forecast of the kinematics and orientations. Amatrice (Fig. 7c): For the ongoing central Apennine seismic sequence of August 24 (Roselli & Mariucci 2016), we consider only three earthquakes relative to 2016 with M ≥ 5.5 that are the most energetic released during the sequence, because almost all the earthquakes have the same NW-NF kinematics. The three earthquakes fit well the forecast of the focal mechanisms and the expected orientation of the faults. Firenze (Fig. 7d): Although with Mw 3.9, we have also considered this event because it occurred in an area usually characterized by few earthquakes and located at ∼30 km southwest of Firenze town (Fig. 1). The strike-slip event agrees with the forecasts of the model. Campobasso (Fig. 7e): The Mw 4.3 Campobasso event shows an NW- NF mechanism. The earthquake is located in the middle of cells showing normal and strike-slip mechanisms. The orientation of T axes is in agreement with the observation. Siracusa (Fig. 7f): This Mw 4.2 strike-slip earthquake is located in a cell showing a prevalent forecast of compressional faulting, with only a minor strike-slip component. However, nodal planes (∼N–S and E–W oriented) and tensional/compressional axis orientations are in agreement with the forecast of the model. In any case, we note that the accuracy of the regions is very low (see Fig. 6), hence some discrepancy may be expected. Ionio (Fig. 7g): This Mw 4.0 strike-slip earthquake, although located at the boundary of the considered area, fits very well the forecast of the nodal plane and its kinematics. Figure 7. View largeDownload slide Comparison between nine observed (black) and forecast (coloured) earthquake focal mechanisms in seven different zones of Italian territory. Red, blue and green lower hemisphere focal mechanisms represent the synthetic NF, TF and SS focal mechanisms computed for the corresponding cell. In the centre of each cell, the slices of the pie chart show the percentage associated to the expected normal (red slices), reverse (blue slices) and strike-slip (green slices) faulting regime 2016 earthquakes: (a) Reggio Emilia (inner northern Apennine, Mw 4.0 December 9), (b) Terni (central Apennine, Mw 4.1 May 30), (c) Amatrice (central Apennine, Mw 6.0 August 24, Mw 5.9 October 26 and Mw 6.5 October 30), (d) Firenze (Tuscany, Mw 3.9 October 25), (e) Campobasso (Molise, Mw 4.3, January 16), (f) Siracusa (Sicily, Mw 4.2 February 8) and (g) Ionio (Ionian-Sea, Mw 4.0 March 6). Figure 7. View largeDownload slide Comparison between nine observed (black) and forecast (coloured) earthquake focal mechanisms in seven different zones of Italian territory. Red, blue and green lower hemisphere focal mechanisms represent the synthetic NF, TF and SS focal mechanisms computed for the corresponding cell. In the centre of each cell, the slices of the pie chart show the percentage associated to the expected normal (red slices), reverse (blue slices) and strike-slip (green slices) faulting regime 2016 earthquakes: (a) Reggio Emilia (inner northern Apennine, Mw 4.0 December 9), (b) Terni (central Apennine, Mw 4.1 May 30), (c) Amatrice (central Apennine, Mw 6.0 August 24, Mw 5.9 October 26 and Mw 6.5 October 30), (d) Firenze (Tuscany, Mw 3.9 October 25), (e) Campobasso (Molise, Mw 4.3, January 16), (f) Siracusa (Sicily, Mw 4.2 February 8) and (g) Ionio (Ionian-Sea, Mw 4.0 March 6). These results show a good agreement between the forecasts and the focal mechanism solution of independent earthquakes, supporting the reliability of the forecasting procedure. This is an important precondition for any practical use of such forecasts, such as, for example, for their use in the next PSHA model for Italy under development (Meletti et al.2017). 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Lett. , 19, 2127– 2130. Google Scholar CrossRef Search ADS   Strasser F.O., Montaldo V., Douglas J., Bommer J.J., 2006. Comment on ‘Influence of Focal Mechanism in Probabilistic Seismic Hazard Analysis’ by Vincenzo Convertito and Andrè Herrero, Bull. seism. Soc. Am. , 96( 2), 750– 753. Google Scholar CrossRef Search ADS   Wortel M.J.R., Spakman W., 2000. Subduction and slab detachment in the Mediterranean-Carpathian region, Science , 290, 1910– 1917. Google Scholar CrossRef Search ADS PubMed  Zoback M.L., 1992. First- and second-order patterns of stress in the lithosphere: the world stress map project, J. geophys. Res. , 97( B8), 703– 728. Zoback M.L., Zoback M.D., 1980. State of stress in the conterminous United States, J. geophys. Res. , 85( B11), 6113– 6156. Google Scholar CrossRef Search ADS   SUPPORTING INFORMATION Supplementary data are available at GJI online. Figure S1. Distribution of C(TOT) and the related position of 33th and 66th percentiles shown in Fig. 6. (a) Histogram of the C(TOT) values obtained from eq. (7), where the 33th (magenta line) and 66th (yellow line) percentiles are shown. (b) Empirical distribution of the C(TOT) values obtained from eq. (7). Table S1. List of 1604 cell coordinates with expected depths, moment tensors and probability of occurrence for each faulting style with prevailing NF, computed by using the TWMT. Table S2. List of 1949 cell coordinates with expected depths, moment tensors and probability of occurrence for each faulting style with prevailing TF, computed by using the TWMT. Table S3. List of 1565 cell coordinates with expected depths, moment tensors and probability of occurrence for each faulting style with prevailing SS, computed by using the TWMT. Please note: Oxford University Press is not responsible for the content or functionality of any supporting materials supplied by the authors. Any queries (other than missing material) should be directed to the corresponding author for the paper. © The Authors 2017. Published by Oxford University Press on behalf of The Royal Astronomical Society.

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Geophysical Journal InternationalOxford University Press

Published: Jan 1, 2018

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