Relocation of recent seismicity and seismotectonic properties in the Gulf of Corinth (Greece)

Relocation of recent seismicity and seismotectonic properties in the Gulf of Corinth (Greece) Summary Recent seismicity (2008–2014) taking place in the Gulf of Corinth and recorded, since the establishment of the Hellenic Unified Seismological Network is relocated in this study. All the available P and S manually picked phases along with the waveforms of 55 broad-band, three-component seismological stations were used. The relocation is performed using the double difference method with differential times derived from phase-picked data and waveform cross-correlation. The accuracy of the relocated catalogue, estimated using a bootstrap approach, is of the order of few hundred metres. In an attempt to define the stress regime in the area, we compute moment tensors of 72 earthquakes with ML ≥ 3.0 and use them to calculate the total seismic moment tensor. A dominant strike of 270° that found in the westernmost part, was changed to 270°–290° at the centre of the gulf, perpendicular to the almost N–S extension of the rift. Further to the east, a gradual change in fault orientation is observed. In the easternmost part, the strike becomes 240°, in agreement with the geometry of the rift. The highly accurate earthquake catalogue, consisting of ∼26 000 events, reveals two patterns of activity in the western Corinth Gulf, namely, strongly clustered seismicity in both space and time in shallow depths and below that activity a very narrow shallow north-dipping seismic zone. Earthquake clusters, mainly located in the western study area, are identified using CURATE algorithm and associated with different north or south-dipping fault segments. The seismicity in the shallow north-dipping seismic zone, defined in detail in this study, is continuous and free of earthquake clusters. This continuous activity most probably defines the boundaries between brittle and ductile layers. The central and eastern parts of the study area mainly accommodate spatiotemporal clusters. Waveform inversion, Seismicity and tectonics, Continental tectonics: extensional, Dynamics: seismotectonics 1 INTRODUCTION The Corinth Gulf (Fig. 1), located in central Greece, is one of the most seismically active areas in Europe (Papazachos & Papazachou 2003; Ambraseys 2009). Its overall shape is an asymmetric half-graben, trending WNW–ESE with its width increasing from a minimum in westernmost part (Psathopyrgos fault, Fig. 1) to a maximum in the central part (Xylokastro fault, Fig. 1; Armijo et al.1996). Geodetic measurements have shown that the extension rate is different in the two parts of the gulf (Billiris et al.1991; Clarke et al.1998; Briole et al.2000; Avallone et al.2004; Chousianitis et al.2015). The western part extends at a rate of 13–14 mm yr−1, with the largest opening rate measured near Aigio fault (Fig. 1, Briole et al.2000). The eastern part is deforming with lower extension rate of approximately 10–12 mm yr−1. Figure 1. View largeDownload slide Morphological map of the Corinth Gulf along with fault segments of: 01—Psathopyrgos, 02—Aigion, 03—Heliki, 04—Offshore Akrata, 05—Xylokastro, 06—Offshore Perachora, 07—Skinos, 08—Alepochori, 09—Kaparelli, 10—Lidoriki, 11—Delphi, 12—Trichonida and 13—Achaia (Armijo et al.1996; Kiratzi et al.2008; Console et al.2013; Karakostas et al.2017). Earthquakes that occurred since 1900 with M ≥ 6.0 and depth ≤ 50 km are shown by stars (Papazachos & Papazachou 2003). Red circles show earthquakes that occurred between 2008 and 2014 and were relocated in this study, whereas green circles show the relocated catalogue of Karakostas et al. (2017). The stations of the Hellenic Unified Seismological Network (HUSN) are displayed by triangles. Inset map: the backarc Aegean sea and the surrounded area, with the dominant seismotectonic features, including the Hellenic trench along with the subduction of the East Mediterranean lithosphere under the Aegean, and the North Anatolian Fault (NAF) which accommodates the westward extrusion of the Anatolian plate into the Aegean. The tectonic setting is supplemented with the existence of the Cephalonia (CTF) and Rhodes (RTF) transform faults. The study area is enclosed in the rectangle. Figure 1. View largeDownload slide Morphological map of the Corinth Gulf along with fault segments of: 01—Psathopyrgos, 02—Aigion, 03—Heliki, 04—Offshore Akrata, 05—Xylokastro, 06—Offshore Perachora, 07—Skinos, 08—Alepochori, 09—Kaparelli, 10—Lidoriki, 11—Delphi, 12—Trichonida and 13—Achaia (Armijo et al.1996; Kiratzi et al.2008; Console et al.2013; Karakostas et al.2017). Earthquakes that occurred since 1900 with M ≥ 6.0 and depth ≤ 50 km are shown by stars (Papazachos & Papazachou 2003). Red circles show earthquakes that occurred between 2008 and 2014 and were relocated in this study, whereas green circles show the relocated catalogue of Karakostas et al. (2017). The stations of the Hellenic Unified Seismological Network (HUSN) are displayed by triangles. Inset map: the backarc Aegean sea and the surrounded area, with the dominant seismotectonic features, including the Hellenic trench along with the subduction of the East Mediterranean lithosphere under the Aegean, and the North Anatolian Fault (NAF) which accommodates the westward extrusion of the Anatolian plate into the Aegean. The tectonic setting is supplemented with the existence of the Cephalonia (CTF) and Rhodes (RTF) transform faults. The study area is enclosed in the rectangle. The Corinth Gulf is bounded to the south by a series of major north-dipping normal faults and a few south-dipping ones at its northern part (Fig. 1). The south faults are, from west to east, the Psathopyrgos, Aigion, Heliki and Xylokastro faults (Fig. 1), with lengths between 15 and 25 km, an average strike of 270°–285° and a northward dip of about 50° near surface (Armijo et al.1996). At the eastern extremity of the gulf, the main fault segments (Offshore Perachora, Skinos and Alepochori, Fig. 1) strike at 250°–270°. Fault plane solutions presented by several researchers (Jackson et al.1982; Taymaz et al.1991; Baker et al.1997; Papazachos et al.1998) support the aforementioned strike and faulting type, in consistency with the rift structure. The west edge of the rift is connected with two major strike-slip faults, north and south of it (Fig. 1). The first one (12 in Fig. 1) is a left-lateral strike-slip fault located near Lake Trichonida, associated with the 1975 M = 6.0 earthquake (Kiratzi et al.2008). The second one (13 in Fig. 1) is a right-lateral strike-slip fault related to the 2008 M = 6.4 Achaia earthquake south of Patraikos Gulf (e.g. Serpetsidaki et al.2014; Karakostas et al.2017). Several destructive earthquakes struck the study area both in historical and instrumental eras (e.g. Papazachos & Papazachou 2003; Ambraseys 2009; Makropoulos et al.2012), with 10 of them with M ≥ 6.0 since 1900 (Fig. 1, Papazachos & Papazachou 2003). Several attempts to record the intense microseismicity in the study area were made in the past three decades. In 1991, a local network consisted of 51 seismological stations was installed in the western Corinth Gulf and operated for two months (Rigo et al.1996; Latorre et al.2004). During the summer of 1993, a temporary seismological network was installed over a period of seven weeks around the eastern Corinth Gulf (Hatzfeld et al.2000). Since 2000, the Corinth Rift Laboratory (CRL) has been in operation in the western part of Corinth Gulf (Lyon-Caen et al.2004; Bernard et al.2006; Lambotte et al.2014). Since 2008, permanent stations of the Hellenic Unified Seismological Network (HUSN) have been in continuous operation with adequate density for microseismicity monitoring and investigation (Fig. 1). The adequate coverage of the seismological networks secures the record of the frequent seismic excitations since 2000. The 2001 Agios Ioannis earthquake swarm took place in the southern part of the study area and was attributed to fluid-driven seismicity (Pacchiani & Lyon-Caen 2010). The next two seismic crises were originated offshore in 2003–2004 and 2006–2007, and for the first one evidence is provided that was related to fluid diffusion process (Bourouis & Cornet 2009; Duverger et al.2015). On 2007 April 08, the Trichonida earthquake swarm initiated near the area where the 1975 M = 6.0 earthquake occurred (Evangelidis et al.2008; Kiratzi et al.2008; Kassaras et al.2014). On 2010 January 18, an earthquake doublet occurred near Efpalio beneath the north coasts of the westernmost part of Corinth Gulf with two Mw = 5.5 events (Karakostas et al.2012; Sokos et al.2012; Ganas et al.2013). On 2013 May 22, an earthquake swarm that initiated near Aigio, with more than 1500 earthquakes detected in three months (Chouliaras et al.2015; Kapetanidis et al.2015; Mesimeri et al.2016; Kaviris et al.2017). The underlying mechanism responsible for the high seismic activity is still under question even though several studies were conducted by different research groups (e.g. Rigo et al.1996; Sorel 2000; Sachpazi et al.2003; Bell et al.2008, 2009; Taylor et al.2011; Godano et al.2014; Lambotte et al.2014; Beckers et al.2015). An outstanding feature revealed from the microseismicity in the area of western Corinth Gulf is the very shallow north-dipping seismic zone. Rigo et al. (1996) observed microseismicity defining the shallow north-dipping seismic zone and interpreted it as a hypothetical detachment zone on which the mapped north-dipping normal faults are rooting. Similar observations have been made since the operation of the CRL network (Lyon-Caen et al.2004; Bernard et al.2006; Lambotte et al.2014). Lambotte et al. (2014), in particular, identified several multiplets that match the geometry of the shallow north-dipping seismic zone. The fault plane solutions of these multiplets also advocate this seismic zone (Godano et al.2014). Lambotte et al. (2014) and Godano et al. (2014) relate the shallow north-dipping seismic zone with the existence of an immature detachment that is currently under development. On the contrary, Hatzfeld et al. (2000) proposed that the seismicity is probably related to the seismic–aseismic transition. A seismic reflection study conducted by Bell et al. (2008) suggests that the shallow geometry is more easily reconciled with a model in which faults are steep to a brittle–ductile transition, at 8–10 km, in agreement with the proposed model by Hatzfeld et al. (2000). Bell et al. (2008) found no evidence of fault listricity in shallower depths, and concluded that the existence of dominant south-dipping faults in their data is incompatible with a low angle north-dipping detachment. In this study, we compiled, for the first time, a highly accurate earthquake catalogue for the entire area of the Corinth Gulf, aiming to contribute to the discussion on the structures governing the seismogenic process. The relocation was performed considering seven years of seismicity (2008–2014) and using differential times from waveform cross-correlation and phase-picked data. We further attempt to interpret the seismotectonic regime in the study area, by combining the relocated earthquake catalogue along with fault plane solutions computed in this study. The contribution to the seismic hazard assessment is the identification of the earthquake clusters and their association with certain fault patches. These fault patches are then compared to the geometry of the major faults for investigating a possible correlation between the occurrence of strong earthquakes and earthquake clusters. The earthquake clusters were also compared with the background seismicity looking for possible patterns in the spatial distribution of earthquakes. 2 EARTHQUAKE RELOCATION PROCEDURE 2.1 Data All the available data (i.e. P, S phases and waveforms) of seven years (2008–2014) seismic activity in the study area are selected. Phases are gathered from the Geophysics Department of the Aristotle University of Thessaloniki (GD-AUTh, http://geophysics.geo.auth.gr/ss/) and the Geodynamics Institute of the National Observatory of Athens (NOA, http://bbnet.gein.noa.gr/HL/). Due to technical reasons, phases from NOA were also collected from the Euro-Mediterranean Seismological Center (http://www.emsc-csem.org/) where they are available in the appropriate format (Godey et al.2006). Then, we merged the bulletins and an initial earthquake catalogue was compiled, containing approximately 24 500 events for the western and 5300 events for the eastern part of the gulf. Regarding the waveforms, the recordings of the HUSN, which is in operation since 2008, are used. Particularly, we selected all the available recordings of 55 broad-band seismological stations with a sampling rate of 100 samples s−1. These recordings were archived in calendar order (approximately 3 TB) and used for the waveform cross-correlation process. Fig. 2 shows the distribution of the P and S phases with the epicentral distances in each subarea. For the western part, where the network is denser, 60 per cent and 93 per cent of the P, and 68 per cent and 96 per cent of the S phases are recorded in stations within distances of 50 and 100 km, respectively. In the eastern part, we observe that 66 per cent and 86 per cent of P, and 75 per cent and 90 per cent of S phases are recorded in distances up to 75 and 100 km, respectively. Figure 2. View largeDownload slide Number of P and S phases against epicentral distance (a) for western and (b) eastern Corinth Rift, respectively. Figure 2. View largeDownload slide Number of P and S phases against epicentral distance (a) for western and (b) eastern Corinth Rift, respectively. 2.2 Relocation process Due to differences in spatial distribution of seismicity, earthquake relocation was performed for each data set separately (western and eastern parts of the study area). For the initial earthquake location, we used the HYPOINVERSE (Klein 2002) software and all the available manually picked P and S phases. The inputs required in this software are a Vp/Vs ratio and an appropriate local velocity model. For defining the Vp/Vs ratio, we applied the Wadati method to two data sets consisting of 411 and 136 earthquakes with more than 20 S phases for each subarea. The resulting Vp/Vs ratio equals to 1.79 and 1.76 for the western and eastern parts, respectively. The 1-D local velocity model used for both subareas (Rigo et al.1996), after testing several crustal models, does not account for lateral variations in the velocity structure. Thus, an important factor in the location is the consideration of station corrections, which improve the performance of the velocity model. Station delays should be carefully calculated especially in large areas, where different type of phases are observed (Pg, Pb and Pn). In our case, it is not possible to calculate stations corrections for all the events simultaneously due to their relatively large interevent distance and the possible mix up of different P phases. For that reason, the two subareas are further divided into smaller parts, based on the spatial distribution of the seismicity. Stations residuals were calculated using HYPOINVERSE software and data sets consisting of the most recent events (2013–2014). After locating the earthquakes with HYPOINVERSE, we calculated a mean residual from all the available P phases and for each station. Then, we locate again the earthquakes taking into account the mean residual for each station and repeat the calculations until the changes in mean values in each station are negligible (Karakostas et al.2012, 2014). The selected data sets include almost all the stations used in this study, as they were gradually added to the network over the years. For a few stations that were not in operation at that time, the corrections were separately calculated. The obtained delays were used for locating all the earthquakes and the resulting solutions are used as input in the double difference method. In order to further improve the obtained locations, we relocate the earthquakes using the double difference package hypoDD (Waldhauser & Ellsworth 2000; Waldhauser 2001). Initially, we computed traveltime differences between the manually picked events in the catalogue, after choosing a maximum number of 10 neighbours per event within a 10 km distance. The event pairs with at least eight observations were kept, since the number of unknowns for one pair of events is eight and a maximum number of observations in each event pair was set equal to 40. This resulted to one million P phase pairs and 740 000 S phases pairs for the western part and 230 000 P phase pairs and 145 000 S phase pairs for the eastern part. An important factor in the application of hypoDD is the determination of the maximum interevent distance between pairs of events. It has been shown that the traveltime error increases with increasing interevent distance (e.g. Waldhauser & Ellsworth 2000; Waldhauser & Schaff 2008). For the phase-picked data, this is mainly caused by heterogeneities in the velocity structure. Considering this effect, we tested several values for maximum separation distance for the two areas. In Fig. 3, the median traveltime residuals are plotted as a function of binned interevent distance for the western and eastern subareas, respectively. The residuals become unstable (i.e. deviation from zero) with increasing distance, which is illustrated in distances greater than 5 km for the western and 6 km for the eastern subarea. These values are used as the maximum distance between linked events in the application of hypoDD for the phase-picked differential times. Figure 3. View largeDownload slide Median residuals against offset in 100 m bins for (a) and (b) phase-picked data and (c) and (d) cross-correlation data for the different parts of the Corinth Gulf. Figure 3. View largeDownload slide Median residuals against offset in 100 m bins for (a) and (b) phase-picked data and (c) and (d) cross-correlation data for the different parts of the Corinth Gulf. The relocated earthquakes obtained from the hypoDD application, using phase-picked data, are considered for preparing the waveforms for the cross-correlation process. Waveforms with 60 s duration, starting from the origin time of each event, were selected and archived by station in calendar order. The resulting database consists of several millions of waveforms for each subarea (∼65 GB). Then, the waveforms were bandpass filtered [2–10 Hz] and updated for P and S phase picks, when available. Cross-correlation measurements were performed in the time domain for all possible event pairs using 1 and 2 s window lengths for both P and S wave trains (Schaff et al.2004; Schaff & Waldhauser 2005). A lag search over ± 1 s was set in order to find the highest value of the correlation coefficient (CC), even if the seismic phases are misidentified. All event pairs with CC above 0.7 (70 per cent) were saved separately for each component, window length and subarea, resulting to several millions of correlation measurements. In order to prepare a robust data set of the acquired correlation measurements and reduce possible outliers, we applied the following restrictions. First, we considered only the event pairs with high similarity, namely CC ≥ 0.8 (80 per cent). Then, we looked for consistency of the measurements made in different window lengths (1 and 2 s). Therefore, we kept delay times based on the 1 s window length, if differences between same event pairs at the different windows are less than the sampling rate (0.01 s). Although all phases were manually picked and no theoretical times were calculated, we used this restriction to avoid bias from the routine analysis and possible misidentification of P and/or S phases. Finally, we selected event pairs with at least 4P or 4S delay time measurements. For the sake of comparison, we used only the differential times derived from waveform cross-correlation and relocated the events with hypoDD. Figs 3(c) and (d) shows that the median of residuals increases with increasing interevent distance for both subareas. According to the residual distribution, we can consider a value for interevent distance of 2–4 km for the cross-correlated data. At the final step of relocation, we exploit the ability of hypoDD to combine differential times derived from phase-picked data and waveform cross-correlation. We performed a joint inversion of all available differential times in order to obtain a highly accurate earthquake catalogue. A crucial part of the relocation process is the weighting and reweighting of the different kind of data (Waldhauser & Ellsworth 2000). For the current data sets, we used four sets with five iterations in each one and appropriate reweighting of the differential times. For the first 10 iterations, we downweight, by a factor of 100, the cross-correlation to allow location using only the catalogue data in larger interevent distances (5–6 km). Then, for the last 10 iterations we downweight, by a factor of 100, the pick data and let the cross-correlation differential times locate the earthquakes having shorter interevent distances (∼2 km). All the calculations were performed using the conjugate gradients method after appropriate damping of the data (LSQR, Paige & Saunders 1982). The final catalogue contains 22 078 events in the western part, almost 90 per cent of the initial events, and 4323 events in the eastern part, almost 88 per cent of the initial catalogue. Events are rejected during the relocation process due to insufficient number of phases and number of links after the application of the weighting function. In the western part, 64 per cent of the earthquakes were located using both cross-correlation and phase-picked data, whereas a remaining 36 per cent using only catalogue data, which mostly concerns earthquakes that occurred in the early period (before 2011) when the available stations were fewer. On the other hand, only 37 per cent of the earthquakes in the eastern part were relocated using both cross-correlation and phase-picked data and 63 per cent of them using only phase-picked data. The low percentage of cross-correlated events is most probably due to the large interevent distances, which results to few cross-correlation pairs. Fig. 4 presents the effect of interevent distance and magnitude difference to the CC. In the western part, the CC decreases with increasing interevent distance (Fig. 4a). A similar pattern is observed in the eastern part (Fig. 4b), where higher CCs were found, and could be considered as the result of cross-correlations concerning seismic excitations very restricted spatially (e.g. Villia sequence, 2013). The CC decreases with increasing difference in magnitude between event pairs in both subareas (Figs 4c and d). In the western part, the CC has a median lower than 90 per cent for ΔM ≤ 1.5, whereas in the eastern part the median approaches 90 per cent for ΔM ≤ 1.5. Figure 4. View largeDownload slide (a) and (b) Mean correlation coefficient against hypocentre separation in 100 m bins and (c) and (d) boxplots of correlation coefficient against difference in magnitude in bins of 0.5. Figure 4. View largeDownload slide (a) and (b) Mean correlation coefficient against hypocentre separation in 100 m bins and (c) and (d) boxplots of correlation coefficient against difference in magnitude in bins of 0.5. Fig. 5 shows the focal distribution obtained for each stage of the relocation process, along a vertical profile in an approximately N–S (195°) direction, almost normal to the dominant fault strike in both subareas. The initial locations derived from the routine analysis of different Institutes (GD-AUTh and NOA) exhibit an undefined cloud of seismicity, placed in depths between 0 and 20 km for both subareas (Figs 5a and b), mainly concentrated between 7 and 13 km for the western part. There are many alignments of the foci along horizontal lines at different depths, which more likely correspond to fixed depths or low resolution of the reported depths. After considering a local velocity model, a Vp/Vs ratio derived from the data and station corrections, the focal distribution is changed (Figs 5c and d). The foci of the western part are confined in a seismogenic zone 5 km thick (6–11 km depths, Fig. 5c) after the inclusion of stations corrections. In the eastern part, a change in focal depths distribution is also observed (Fig. 5d). The foci alignment is not observed in this stage. The relocation results after the application of hypoDD with the phase-picked data are shown in Figs 5(e) and (f). The seismogenic zone in the western region seems to be narrower without any significant shift in the cluster centroid (Fig. 5e). The final locations are shown in Figs 5(g) and (h), where the improvement in the locations is clearly shown. The seismogenic zone in the western part is still confined in the depth range 6–11 km (Fig. 5g). In the eastern part, the interevent distances are reduced but the seismicity is not concentrated at certain depths, instead it is evenly distributed between 3 and 13 km. Figure 5. View largeDownload slide Different stages of relocation process for the two areas of Corinth Gulf. (a) and (b) Initial location obtained from routine analysis, (c) and (d) application of single-event location with station corrections, (e) and (f) application of hypoDD with phase-picked data and (g) and (h) final locations after joint inversion of cross-correlation measurements and phase-picked data. Figure 5. View largeDownload slide Different stages of relocation process for the two areas of Corinth Gulf. (a) and (b) Initial location obtained from routine analysis, (c) and (d) application of single-event location with station corrections, (e) and (f) application of hypoDD with phase-picked data and (g) and (h) final locations after joint inversion of cross-correlation measurements and phase-picked data. 2.3 Error estimation Errors in the final locations estimated by hypoDD, using the LSQR method, are not representative of the real location errors (Waldhauser 2001). Their values are of the order of few metres (3–5 m) and have no physical meaning. In order to estimate the accuracy of the final locations, we perform error analysis concerning the time delay uncertainties and the effect of the station distribution to the final locations. First, a bootstrap resampling method (Efron 1982) is applied by creating 200 samples, with replacement, of the final residual vector derived from the double difference joint inversion. The residuals are then added to all differential traveltimes with unit weights and the relocation is repeated for each sample. The distribution of the differences between the final locations and the 200 samples is used to compute the 95 per cent confidence error ellipse per event. Table 1 summarizes the uncertainty estimates for each direction, type of data and subarea. It is observed that median errors are larger in the eastern part, whereas in the western part they are of the order of few hundred metres. In addition, it is shown that for both areas the phase-picked data have larger uncertainties than events located using both cross-correlation and phase-picked data. Table 1. Median errors of the relocated catalogue in the three directions for the different parts of Corinth Gulf and the different type of data (phase-pick and cross-correlation). All errors are in metres.   Western part  Eastern part  Direction  All  Phase pick  CC  All  Phase pick  CC  X  380  660  282  856  1230  617  Y  260  439  190  629  864  441  Z  300  513  221  655  933  436    Western part  Eastern part  Direction  All  Phase pick  CC  All  Phase pick  CC  X  380  660  282  856  1230  617  Y  260  439  190  629  864  441  Z  300  513  221  655  933  436  View Large Taking into account that the most recent earthquakes are located using cross-correlation differential times, we looked for any significant temporal variations in the errors. Fig. 6 shows the median errors in the three directions as a function of time for the two types of data (phase-picked and cross-correlation) in each subarea separately. The median errors are calculated within a moving window of 300 events and step of five events. For the western part (Fig. 6, upper panel), the errors for the cross-correlated data are decreasing with time. On the other hand, the phase-picked data have larger errors for the entire period with an increasing trend in the late years. This is due to the lower accuracy of the few remaining events relocated with phase data compared to cross-correlated ones. For the eastern part of the gulf (Fig. 6, lower panel), we do not observe a decreasing trend of error uncertainties with time. However, in two cases, which are associated with certain seismic excitations occurred in 2011 and 2013, respectively, a decrease in error is illustrated. This is mainly due to the high density of seismic activity in both excitations. The spatial distribution of the errors in three directions evidences that errors are smaller in areas where seismic activity is denser (Fig. C1). Figure 6. View largeDownload slide Median error in the three directions as a function of time for the phase-picked data (red lines) and the cross-correlated one (black lines) for the western (upper panel) and eastern Corinth Gulf (lower panel), respectively. Figure 6. View largeDownload slide Median error in the three directions as a function of time for the phase-picked data (red lines) and the cross-correlated one (black lines) for the western (upper panel) and eastern Corinth Gulf (lower panel), respectively. The effect of station distribution in the final locations is tested by applying a jackknife method (Efron 1982). Particularly, we repeat the relocation process of the initial data set by omitting one station at a time (Waldhauser & Ellsworth 2000). Then, we calculate the standard deviation of the differences between the initial locations and the ones obtained from the jackknife method for each event in the three spatial directions. The median errors for the western part are 101, 68 and 79 m for the two horizontal and the vertical directions, respectively. These values are significantly smaller than the ones introduced by noise in the data in bootstrapping method. The median errors in the eastern part are 123, 132 and 446 m for the three directions, respectively, implying that the network geometry affects the final locations. 3 MOMENT TENSORS Focal mechanisms are computed on a routine basis, for events with ML ≥ 4.0 occurring in the broader area of Greece, using regional or local data and different algorithms for waveform inversion (Konstantinou et al.2010; Roumelioti et al.2011; Serpetsidaki et al.2016). For the area of Corinth Gulf, several studies with fault plane solutions were performed, using P-wave onsets from a local network (e.g. Rigo et al.1996; Hatzfeld et al.2000; Godano et al.2014) or after studying a certain seismic excitation (e.g. Hatzfeld et al.1996; Karakostas et al.2012; Kapetanidis et al.2015; Mesimeri et al.2016). Waveform inversion techniques were also applied in the study area in order to compute fault plane solutions for moderate to strong events in several cases (e.g. Baker et al.1997; Evangelidis et al.2008; Zahradnik et al.2008; Sokos et al.2012). Aiming to obtain a reliable and homogeneous data set of fault plane solutions for the study area, we used the ISOLA software (Sokos & Zahradnik 2008, 2013) to compute centroid moment tensors for ML ≥ 3.0 events that occurred between 2011 and 2014. ISOLA uses the iterative deconvolution method of Kikuchi & Kanamori (1991) modified for regional distances. The set of stations used for relocation purposes is considered here along with the velocity model proposed by Rigo et al. (1996). The inversion was performed for a deviatoric moment tensor and the waveforms are filtered to a frequency range of 0.03–0.09 Hz. From the 58 events of the relocated catalogue with ML ≥ 3.5, we computed 50 moment tensors (86 per cent). Due to the density of the network, we were able to look for possible moment tensors for events within the magnitude range 3.0 ≤ ML < 3.5. Even though it is difficult to determine fault plane solutions for smaller magnitude earthquakes, we computed 22 focal mechanisms out of 116 events with 3.0 ≤ ML < 3.5 (∼18 per cent). The spatial distribution of the 72 focal mechanisms is shown in Fig. 7 and relevant information is provided in Appendix  A. Figure 7. View largeDownload slide Fault plane solutions obtained in this study. The boxes define the different subregions used for the estimation of the TSMT. Inset panel: TSMT solutions for the different subregions. Figure 7. View largeDownload slide Fault plane solutions obtained in this study. The boxes define the different subregions used for the estimation of the TSMT. Inset panel: TSMT solutions for the different subregions. At the latest version of ISOLA package, the user has the ability to estimate the quality and the uncertainties of the computed moment tensors using several quantitative criteria (Sokos & Zahradnik 2013). The first two estimated factors after the waveform inversion are the variance reduction (VR), which reflects the similarity between the synthetic and the observed waveforms, and the condition number (CN), which measures the stability of the inversion. Two additional indicators of solution quality regarding the space–time variability of the solution could be obtained. Focal-Mechanism Variability Index (FMVAR), which compares the obtained solutions with the optimal solution using the Kagan angle (Kagan 1991), and Space-Time Variability Index (STVAR), which measures the size of the space–time area corresponding to the given correlation threshold. The solutions with low values of FMVAR (<30) and STVAR (<0.30) are considered more stable. The aforementioned quantitative criteria are estimated for the 72 moment tensors computed in this study, which have CN < 7 with a mean value of 2.74 and mean VR equal to 0.5. The mean values of the FMVAR and STVAR parameters are 9.0 and 0.19, respectively, supporting solutions stability. For the 82 per cent of the solutions six or more stations are taken, a number which is considered quite satisfactory for the waveform inversion. The mean percentage participation of the double-couple component in the moment tensor is 85 per cent for the 72 moment tensors. In order to quantify the stress regime in the study area, we calculated the total seismic moment tensor (TSMT), which is the sum of the moment tensors calculated from the individual solutions   \begin{equation} M_{ij}^{{\rm{total}}} = \sum\limits_{k = 1}^N {M_0^km_{ij}^k} \end{equation} (1)where k is the number of earthquakes, M0 the scalar seismic moment of each event and mij the seismic moment tensor components (Buforn et al.2004). TSMT, compared to other approaches (e.g. Frohlich & Apperson 1992), has the advantage of taking into consideration the magnitude of each earthquake and using it as a weighting factor. As a result, the earthquakes with high M0 values have the largest contribution in the estimation of TSMT. The study area is now divided into eight subregions based on the spatial extent of the major faults in the area and the spatial distribution of the focal mechanisms (Fig. 7). For each subregion, we estimate the TSMT using only the focal mechanisms computed in this study (Fig. 7 inset panel and Table 2). Starting with the westernmost part north of the Patraikos Gulf (subregion 01), where the dominant structure is a left-lateral strike-slip fault (Evangelidis et al.2008; Kiratzi et al.2008; Kassaras et al.2014), we observe a right-lateral strike-slip motion near the Lake Trichonida, which is orthogonal to the left-lateral structure. Normal faults are prevalent in Corinth Gulf striking from 260° and gradually reaching 290° at the eastern edge. The mean strike in subregion 02 is 260°, where the Psathopyrgos fault is located, equal to 277° in subregion 03 (Aigion fault). In subregions 05, 06 and 07 the mean strikes are equal to 298°, 298° and 273°, respectively, showing a change in faulting orientation from north to south. The major faults in the area (Offshore Akrata, Xylokastro and Offshore Perachora) have a strike of 280°–290°, similar with that obtained from TSMT analysis in the southern part of the area. In 2013 May, an earthquake swarm took place in subregion 04 with more than 1500 earthquakes occurring in only months, revealing microstructures striking almost E-W. The focal mechanisms obtained here, using the ISOLA package and the waveform inversion method, are in accordance with those computed using P-wave onsets (Kapetanidis et al.2015; Mesimeri et al.2016) for events with smaller magnitudes (ML > 2.0). At the easternmost part (subregion 08), the TSMT reveals normal faulting striking SW–NE (240°). Table 2. Total Seismic Moment Tensor solutions (TSMT) for each subregion along with the number of fault plane solutions (FPS) used and the CLVD percentage.       Plane 1  Plane 2  T-axis  P-axis  Subregion  Number of FPS  CLVD (per cent)  Strike (°)  Dip (°)  Rake (°)  Strike (°)  Dip (°)  Rake (°)  Trend (°)  Coplunge (°)  Trend (°)  Coplunge (°)  01  3  16  63  66  174  155  85  25  21  69  286  77  02  23  15  263  43  −84  76  48  −95  169  87  292  5  03  24  3  277  27  −86  93  63  −92  185  72  359  18  04  5  1.5  271  36  −86  87  54  −92  179  81  347  9  05  5  2  289  71  −49  40  44  −152  351  74  242  43  06  6  1  298  22  −70  96  70  −98  193  66  354  25  07  4  5  273  31  −95  98  59  −87  186  76  16  14  08  2  2  240  42  −87  56  48  −93  148  87  297  4        Plane 1  Plane 2  T-axis  P-axis  Subregion  Number of FPS  CLVD (per cent)  Strike (°)  Dip (°)  Rake (°)  Strike (°)  Dip (°)  Rake (°)  Trend (°)  Coplunge (°)  Trend (°)  Coplunge (°)  01  3  16  63  66  174  155  85  25  21  69  286  77  02  23  15  263  43  −84  76  48  −95  169  87  292  5  03  24  3  277  27  −86  93  63  −92  185  72  359  18  04  5  1.5  271  36  −86  87  54  −92  179  81  347  9  05  5  2  289  71  −49  40  44  −152  351  74  242  43  06  6  1  298  22  −70  96  70  −98  193  66  354  25  07  4  5  273  31  −95  98  59  −87  186  76  16  14  08  2  2  240  42  −87  56  48  −93  148  87  297  4  View Large 4 DETERMINATION OF ACTIVE SEGMENTS AND SEISMOTECTONIC PROPERTIES In an attempt to identify the active fault segments in the study area by exploiting the high accuracy of the relocated seismicity, we looked for seismic excitations that took place in the Corinth Gulf during the time span of the relocated catalogue. The identification of seismic excitations, known as earthquake clusters, is performed using the CURATE algorithm (Jacobs et al.2013) on the relocated earthquake catalogue. CURATE focuses on periods when the seismicity rate is increased above the background rate in a given area, and identifies earthquake clusters by applying an interevent distance and day rule for each earthquake in the catalogue. Taking into consideration, the errors in hypocentre locations, calculated using the bootstrap method, we set a distance rule for the CURATE algorithm equal to 2 km for the western subarea. We chose a low value due to the high location accuracy and spatial density of the earthquakes, which are mainly associated with small fault segments. For the eastern part, the distance rule was set to 4 km due to the larger location errors. The day rule was set to two days for both subareas. The identified spatiotemporal clusters are initially filtered based on the number of events (N ≥ 10). Then, it was attempted to relate them to fault segments by constructing several cross-sections normal to a wide range of strikes for each identified cluster. The cross-section in which the foci delineate a seismogenic zone is selected as the most appropriate one in each case and the dip for each selected cross-section was measured. The search for earthquake clusters is performed for each subarea separately and a correlation between their spatial distribution and seismicity in the area is attempted. 4.1 Western Corinth Gulf In the western Corinth Gulf 185 clusters with 10 or more earthquakes are identified by CURATE algorithm, with 47 of them being related to fault segments dipping north (37) and south (10) with angles ranging from 30° to 65° and striking in the range 220°–300° and 90°–110°, respectively. The differences between the strikes and dips of the identified segments, and the TSMT solutions are shown in Table B1. The deviations indicate that seismic excitations take place not in patches of the major faults which are locked but in patches of buried/blind secondary faults in the area. In Fig. 8, the identified clusters with N ≥ 10 which occurred since 2011 are plotted (green circles) along with the clusters that are associated with a fault segment (red circles) and the background activity (white circles). The majority of the clusters are located offshore with only few onshore exceptions. It is notable that several clusters are located north of the fault associated with the 1995 Aigion Mw 6.5 earthquake (Bernard et al.1997), whereas a lack of earthquake clusters is observed north of the westernmost edge of Psathopyrgos fault. Forty two (42) of the 47 identified segments are associated with seismic excitations that occurred after 2011, indicating that the earlier locations or the network detectability were not adequate for defining fault segments. Figure 8. View largeDownload slide Spatial distribution of the relocated catalogue occurred since 2011 in the western Corinth Gulf along with the major faults in the area (see Fig. 1). White circles show seismicity that is not part of a cluster, green circles show events that are members of a cluster with N ≥ 10, whereas red circles show the clusters that are associated with a fault segment. The epicentres of the Aigio 2013 earthquake swarm obtained from Mesimeri et al. (2016) are depicted with magenta. The traces of the fault segments at the mean depth of each cluster are shown with thick black lines and thin black lines correspond to the vertical cross-sections shown in Fig. 9. Figure 8. View largeDownload slide Spatial distribution of the relocated catalogue occurred since 2011 in the western Corinth Gulf along with the major faults in the area (see Fig. 1). White circles show seismicity that is not part of a cluster, green circles show events that are members of a cluster with N ≥ 10, whereas red circles show the clusters that are associated with a fault segment. The epicentres of the Aigio 2013 earthquake swarm obtained from Mesimeri et al. (2016) are depicted with magenta. The traces of the fault segments at the mean depth of each cluster are shown with thick black lines and thin black lines correspond to the vertical cross-sections shown in Fig. 9. We constructed a set of 20 cross-sections (Fig. 9) normal to the main strike of the rift, taking into account the major north-dipping faults, the fault plane solutions and the TSMTs computed in this study, in order to correlate the earthquake clusters with the spatial distribution of seismicity. Considering the time dependency of the errors, we plot the events which occurred between 2008 and 2010 in the background (grey circles) in order to compare them with the ones that occurred later (2011–2014, black circles). Earthquakes belonging to clusters were plotted as in the map of Fig. 9. Figure 9. View large Download slide View large Download slide Set of 20, normal to the main trend of the gulf, cross-sections as denoted in Fig. 8. Black dots show the earthquakes that occurred since 2011, whereas grey dots show the seismicity from 2008 to 2010. Green dots show the clusters with N ≥ 10, red dots show the clusters related to a fault segment and magenta dots show the Aigio 2013 earthquake swarm (Mesimeri et al.2016). Black lines indicate the major faults. The width of each cross-sections is 3 km. Figure 9. View large Download slide View large Download slide Set of 20, normal to the main trend of the gulf, cross-sections as denoted in Fig. 8. Black dots show the earthquakes that occurred since 2011, whereas grey dots show the seismicity from 2008 to 2010. Green dots show the clusters with N ≥ 10, red dots show the clusters related to a fault segment and magenta dots show the Aigio 2013 earthquake swarm (Mesimeri et al.2016). Black lines indicate the major faults. The width of each cross-sections is 3 km. The earthquakes of the first two cross-sections (W01 and W02) are located in the Patraikos Gulf, where the seismicity is sparse and the dominant strike differs from the rest of the study area. The foci distribution is comprised into almost vertical groups of seismicity, which have been identified as spatiotemporal clusters but are not associated with a fault segment, and clusters (red circles) defining segments striking at 250°–260°. The W03–W20 cross-sections are normal to a mean strike of 285°N, even though the segments defined by the earthquake clusters have variable strikes. In cross-sections W03–W05, earthquake clusters and background activity occur at focal depths of 7–12 km. A different pattern is illustrated in the next four cross-sections (W06–W09), where the most recent events (black circles) form a very narrow, shallow north-dipping zone, which initially has a shorter length but becomes longer as we move to the east. The earthquake clusters that are associated with fault segments (red circles) or they do not define any structure (green circles) occur at shallower depths. Few events belonging to spatiotemporal clusters that are found very close to the narrow zone are located with larger errors (>300 m), whereas their cluster centroid is shallower. It is also noteworthy that the earthquakes in this cross-section are located in the area between the two major faults Aigion and Psathopyrgos (Fig. 8). Comparison between the two data sets, namely, the 2008–2010 (grey dots in Fig. 9) and 2011–2014 (black dots in Fig. 9), shows that the earlier ones form a cloud around the later ones, revealing the location improvement with time. Moving further to the east (W10–W14) across the Aigion fault, we observe that the defined clusters and the background activity are located at the same depths. A different pattern is observed during the 2013 Aigion swarm (magenta circles), illustrated in cross-sections W12–W14 (Fig. 9). This cross-section contains the well-studied earthquake swarm, which was initiated in 2013 May and lasted almost three months (Chouliaras et al.2015; Kapetanidis et al.2015; Mesimeri et al.2016; Kaviris et al.2017). It reveals a north-dipping structure at the southern part of the western Corinth Gulf. This activity is located south of the shallow north-dipping seismic zone and could not be associated with the offshore activity. Finally, east of W14 cross-section, the last six cross-sections (W15–W20) were constructed in an area with sparse seismicity where the association of clusters with active fault segments is not feasible. As we reach the eastern part of Corinth Gulf, the seismicity is reduced and this pattern continues to the eastern Corinth Gulf. 4.2 Eastern Corinth Gulf After applying the CURATE algorithm 35, spatiotemporal clusters with at least 10 events are identified and two of them are related to a certain fault segment. The first cluster that is related to a fault segment occurred in 2009 May following an ML = 4.4 earthquake. The second one refers to the Villia sequence that occurred in 2013 June near Kaparelli fault and lasted approximately one month (Kaviris et al.2014, Appendix  B). In Fig. 10, we show the spatial distribution of the background activity (white circles) along with the identified spatiotemporal clusters with N ≥ 10 (green circles) and those that are related to fault segments (red circles). As in the western part, we consider only events since 2011 due to the improvement in the location accuracy. Figure 10. View largeDownload slide Spatial distribution of the relocated catalogue for the eastern Corinth Gulf along with the major faults in the area. The notation is the same as in Fig. 8. Figure 10. View largeDownload slide Spatial distribution of the relocated catalogue for the eastern Corinth Gulf along with the major faults in the area. The notation is the same as in Fig. 8. A set of 18 cross-sections (Fig. 10) are constructed normal to the main orientation of the eastern part keeping the same notation as in Fig. 9. A clear difference in the seismicity distribution is observed, compared to the western part. In the first 15 cross-sections (Fig. 11), we could not define any structure, but a pattern of vertical distributions of foci, which in several cases are identified as spatiotemporal clusters (green circles), is depicted. An example of this pattern is the E06 cross-section, which shows two vertical groups of foci in different depths (green circles). Most of these events occurred in 2012 September following an Mw = 5.1 earthquake. Due to the vertical distribution of the foci, we looked for a possible relation to fluid intrusion by applying distance–time plots. These plots, in cases of fluid intrusion, describe the migration of seismicity, which is evident by a characteristic triggering front (Shapiro 2015). However, for this particular sequence, we did not find evidence for fluid migration, whereas a further examination of fluid intrusion in the eastern Corinth Gulf is beyond the scope of this study. Figure 11. View largeDownload slide Set of 18, normal to the main trend of the gulf, cross-sections as denoted in Fig. 10. The notation is the same as in Fig. 9. Figure 11. View largeDownload slide Set of 18, normal to the main trend of the gulf, cross-sections as denoted in Fig. 10. The notation is the same as in Fig. 9. At the easternmost part of the study area, the dominant fault strike is again changing, also shown by the TSMTs. The final three cross-sections (E16–E18) include the 2013 Villia sequence (E17 red circles) and two sequences that occurred in 2009 (E18 grey circles) and 2013 (E16 green circles), respectively. A south-dipping structure related to the Villia sequence (2013 June) is shown in cross-section E17, located at focal depths of 7–9 km. The 2009 sequence located south of the Villia sequence forms an almost vertical structure confined in shallower depths, very close to the surface. Due to the sparse seismicity in the area, with only two exceptions, the location accuracy is not adequate for making strong conclusions about the active structures in the area. 5 DISCUSSION A highly accurate earthquake catalogue for the area of Corinth Gulf is compiled for the first time, using the data of the HUSN from 2008 to 2014. Approximately 22 000 events are located in the western study area, which is twice the number of events in the relocated catalogue of Lambotte et al. (2014) which however covers a different time period (2000–2007). Additionally, for the first time a massive relocation of recent seismicity has been performed for the eastern Corinth Gulf (∼4000 events). The catalogue is considered highly accurate, especially in the western Corinth Gulf, with the uncertainty in horizontal and vertical directions of the order of few hundred metres. The major finding of this study is that the spatial distribution of the relocated seismicity revealed two patterns of activity in the western subarea, namely, strongly clustered seismicity in both space and time in depths shallower than 10 km and below that activity a very narrow shallow north-dipping zone void of spatiotemporal clusters. The earthquake clusters identified in the western subarea, after applying certain space–time criteria, were examined and related to 47 fault segments having variable strikes and dipping either to the north or to the south. The majority of the clusters are located offshore between 22.00° and 22.20°Ε with high dip angles [40°–60°], strikes of 270°–290° and their depths in the range 6–10 km. In the westernmost part of the study area, few clusters are aligned at slightly different strikes [250°–270°]. The north-dipping seismic zone observed in several previous seismicity studies (Rietbrock et al.1996; Rigo et al.1996; Hatzfeld et al.2000; Lyon-Caen et al.2004; Bernard et al.2006; Lambotte et al.2014) is also identified in this study, particularly in the W06–W09 (Figs 8 and 9) cross-sections. However, the underlying mechanism that triggers the seismicity in this seismic zone has been questioned for over three decades. We found here that the observed shallow north-dipping seismic zone is free of spatiotemporal earthquake clusters and the activity is continuous throughout the study period. The space–time-clustered events (earthquake clusters) are located in different parts of the rift, whereas only a few of them are located above the shallow north-dipping seismic zone in shallower depths. Assuming that the multiplets defined by Lambotte et al. (2014) are comprised in the same shallow north-dipping seismic zone that is found in this study, we observe that these multiplets last several years, and in a few cases, span the entire period of the CRL operation (table A1 in Lambotte et al.2014). Additionally, there is no seismic activity below the shallow north-dipping seismic zone, as it is illustrated in the cross-sections (Fig. 9). Thus, the continuous microseismic activity, observed only in the western part of Corinth Gulf, most probably defines the seismic–aseismic transition (Hatzfeld et al.2000). The seismicity in the eastern subarea is relatively low and highly sparse compared to the western Corinth Gulf. Two out of the 35 spatiotemporal clusters identified in the study period are related to a certain fault segment. The most recent cluster related to a fault segment occurred in 2013 June, lasted almost one month and comprised some hundreds events with magnitudes 0.5 ≤ ML ≤ 3.5 (cluster E01, Table B1). This activity forms a south-dipping structure (E17 in Fig. 11) and exhibits similar characteristics as the Kaparelli fault, which was activated during the 1981 Alkyonides sequence (Papazachos et al.1984; King et al.1985). In a few cases (E06 and E18 in Fig. 11), it appeared that seismic activity is clustered in shallow depths and forms almost vertical lines, which could not be attributed to any known fault segment. However, the location uncertainty, the limited data, as well as the local network geometry are not favourable for making strong conclusions. The moment tensors computed for 72 earthquakes using waveform inversion techniques and the fault plane solutions are in accordance with the N–S extension of the rift. We followed a different approach from Godano et al. (2014) as we considered events with M ≥ 3.0 for the entire Corinth Gulf regardless of their correlation with earthquake clusters. However, the results of both studies are quite similar for the central part of the western subarea. The computation of total moment seismic tensor for eight different subregions revealed gradual strike changes from west to east. The seismic activity is still on near Trichonida Lake with few strike-slip fault plane solutions, which exhibit SW–NE orientation, perpendicular to the spatial alignment of the 1975 aftershock sequence and the 2007 swarm (Kiratzi et al.2008; Kassaras et al.2014). The faults of the westernmost and the easternmost extremities are striking almost at 250°. 6 CONCLUSIONS A firm conclusion traced in this study is that the difference in seismicity between the two parts of the Corinth Gulf is clearly depicted and can be attributed to the different extension rates estimated from geodetic data. The highly accurate catalogue defines in great detail the existence of a shallow north-dipping seismic zone which lacks of spatiotemporal earthquake clusters and is characterized by continuous seismic activity. It is evident that the seismic activity ceases below this structure and the lower depth can be interpreted as the boundary between the seismic and aseismic layers. The absence of recent strong earthquakes (M > 6.0) in the dominant faults (Psathopyrgos and Aigion) along with spatially clustered continuing activity raises questions about the possibility of creeping faults in that area. Thus, the full exploitation of the recorded seismic activity, the catalogue compilation and its future updates will be a valuable tool in the direction of understanding the underlying mechanism of earthquake process in the Corinth Gulf and constitutes an indispensable component for any seismic hazard assessment study. 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Google Scholar CrossRef Search ADS   APPENDIX A: FAULT PLANE SOLUTIONS Table A1. Fault plane solutions for 72 events with ML ≥ 3.0 occurred in the Corinth Gulf in 2011–2014.                   Plane 1  Plane 2  P-axis  T-axis            Year  Date  Origin time  Latitude (°N)  Longitude (°E)  Depth (km)  ML  Mw  M (N m)  Strike (°)  Dip (°)  Rake (°)  Strike (°)  Dip (°)  Rake (°)  Trend (°)  Plunge (°)  Trend (°)  Plunge (°)  VR  CN  N  FMVAR  STVAR  2011  02 05  02:52:38.47  38.4179  22.0244  7.79  3.5  3.6  3.662 × 1014  307  70  −79  97  22  −118  234  63  28  25  0.18  3.4  7  8  0.12  2011  02 11  17:56:56.00  38.3932  21.7899  10.12  4.2  4.0  1.407 × 1015  129  90  −25  219  65  −180  81  17  176  17  0.70  2.1  10  9  0.24  2011  02 12  11:37:36.58  38.3897  21.7895  10.99  3.6  3.7  3.999 × 1014  224  71  168  319  78  20  91  5  183  22  0.32  1.9  9  10  0.23  2011  02 20  19:24:07.94  38.4991  21.6624  14.46  3.3  3.6  2.842 × 1014  75  72  −179  344  89  −18  298  14  31  12  0.50  2.3  8  8  0.24  2011  02 20  21:57:16.62  38.5002  21.6627  14.36  3.7  3.7  3.958 × 1014  341  85  −31  74  59  −174  293  25  31  18  0.54  2.3  9  9  0.23  2011  02 24  23:29:46.08  38.3904  21.8013  10.71  3.7  3.6  3.390 × 1014  126  59  −22  228  71  −147  91  36  355  7  0.27  3.0  7  21  0.33  2011  04 13  02:32:27.09  38.2667  22.1924  9.68  3.4  3.4  1.394 × 1014  269  19  84  83  71  −92  349  64  174  26  0.27  2.6  5  7  0.09  2011  05 04  12:39:42.86  38.2867  22.3976  13.27  4.0  3.8  6.153 × 1014  89  60  −88  264  31  −94  5  75  177  15  0.62  1.9  7  7  0.20  2011  05 04  14:35:15.76  38.3457  21.8141  9.90  3.6  3.4  1.881 × 1014  242  23  −140  114  75  −72  48  56  190  28  0.42  4.0  7  9  0.11  2011  06 06  11:06:01.57  38.4366  21.8307  13.09  3.4  3.4  1.672 × 1014  257  26  −106  94  65  −83  19  69  178  20  0.54  2.6  5  6  0.24  2011  06 07  23:39:15.06  38.4318  22.0633  6.55  3.3  3.2  7.355 × 1013  256  28  −83  68  63  −94  330  72  161  18  0.62  5.4  5  9  0.03  2011  07 18  03:58:51.62  38.2368  22.5373  19.19  3.3  3.3  9.813 × 1013  305  34  −54  83  63  −111  316  65  189  16  0.43  1.9  6  13  0.21  2012  07 16  20:26:48.44  38.3947  22.0013  9.64  3.1  3.3  1.161 × 1014  291  28  −79  99  63  −96  356  72  193  18  0.57  2.1  6  5  0.26  2012  08 16  21:22:54.36  38.2661  22.5302  14.40  3.5  3.7  4.153 × 1014  234  57  −131  111  50  −45  87  57  351  4  0.36  1.7  9  7  0.26  2012  09 08  16:40:14.70  38.3757  22.0631  10.59  3.7  3.5  2.456 × 1014  322  30  −56  104  66  −108  343  65  207  19  0.28  1.8  8  8  0.30  2012  09 19  00:55:36.94  38.351  22.3146  15.51  3.1  3.3  1.239 × 1014  299  31  −64  89  63  −105  330  69  190  17  0.53  1.9  4  9  0.28  2012  09 21  15:21:21.12  38.3534  22.0147  8.41  3.9  3.9  8.287 × 1014  292  23  −75  95  67  −96  354  67  190  22  0.59  1.9  10  7  0.20  2012  09 22  03:52:24.52  38.0740  22.7446  15.99  5.1  4.9  2.660 × 1016  300  21  −68  96  71  −98  353  63  193  25  0.60  1.7  12  8  0.29  2012  10 18  19:27:53.28  38.5509  21.9171  18.69  3.1  3.3  1.319 × 1014  238  48  −131  110  56  −54  77  61  175  4  0.44  1.9  5  4  0.22  2012  12 09  01:23:06.11  37.9479  22.6038  10.28  4.1  4.0  1.313 × 1015  271  30  −97  99  60  −86  19  75  186  15  0.46  1.8  9  5  0.21  2012  12 27  23:20:53.86  38.2181  21.8490  9.06  3.8  3.9  9.652 × 1014  255  35  −138  128  68  −63  76  58  198  18  0.80  2.0  10  13  0.26  2013  01 28  04:14:06.67  38.3250  22.1627  9.52  3.6  3.7  4.707 × 1014  277  27  −83  89  63  −94  351  72  182  18  0.54  2.1  12  11  0.21  2013  05 19  12:00:41.08  38.3916  21.7607  13.88  3.1  3.3  1.013 × 1014  203  46  −135  78  60  −54  40  58  143  8  0.27  2.4  8  11  0.23  2013  05 28  01:13:00.49  38.2261  22.1059  9.85  3.6  3.6  3.109 × 1014  287  42  −67  78  52  −109  290  74  181  5  0.44  2.7  9  8  0.17  2013  05 31  08:57:25.28  38.2293  22.1097  10.14  4.0  3.7  3.856 × 1014  226  26  −112  71  66  −79  0  67  153  20  0.44  2.2  10  5  0.23  2013  06 11  19:36:16.60  38.1590  23.1956  10.00  3.5  3.6  3.128 × 1014  252  26  −73  54  65  −98  307  69  150  20  0.36  1.8  8  10  0.25  2013  06 27  17:24:43.40  38.2169  22.1197  9.18  3.8  3.8  5.454 × 1014  103  48  −91  285  42  −89  358  87  194  3  0.53  2.0  7  8  0.24  2013  07 09  21:46:19.96  38.4156  21.9633  9.80  3.1  3.2  8.332 × 1013  282  26  −75  85  65  −97  340  70  181  19  0.44  3.0  6  13  0.27  2013  07 14  07:46:58.39  38.2298  22.0917  10.95  3.3  3.5  2.006 × 1014  256  40  −105  95  51  −78  57  79  176  5  0.85  3.2  5  24  0.22  2013  07 24  02:55:49.81  38.2298  22.0986  10.98  3.5  3.7  4.312 × 1014  263  39  −98  94  51  −83  41  82  179  6  0.70  2.1  9  6  0.16  2013  09 20  02:05:19.26  38.1670  23.1052  13.42  4.4  4.4  4.304 × 1015  56  47  −92  238  43  −88  301  87  147  2  0.34  2.0  11  6  0.25  2013  09 26  02:34:36.34  38.3019  22.1353  8.39  3.7  3.8  7.233 × 1014  261  25  −103  95  65  −84  17  69  181  20  0.81  2.5  6  6  0.13  2013  09 26  05:25:12.02  38.2999  22.1292  8.85  3.1  3.1  6.028 × 1013  246  21  −121  99  73  −79  26  61  180  27  0.40  2.5  5  12  0.21  2013  10 22  03:38:57.90  38.3669  21.8797  8.19  3.1  3.1  9.891 × 1013  131  59  −13  227  79  −148  93  30  355  13  0.76  2.7  6  13  0.22  2013  12 09  08:59:35.62  38.3807  21.7454  14.54  3.7  3.6  3.308 × 1014  64  47  −74  221  45  −106  47  78  143  1  0.54  1.7  7  6  0.19  2013  12 22  18:04:02.94  37.8548  22.7335  13.74  3.5  3.6  3.080 × 1014  293  36  −82  103  54  −96  349  80  197  9  0.23  1.4  6  5  0.29  2014  01 24  22:08:48.30  38.3374  21.9980  7.91  3.8  3.8  6.244 × 1014  311  49  −65  96  47  −115  291  72  24  1  0.48  3.6  9  9  0.09  2014  01 29  09:14:23.47  38.3411  21.9822  8.48  3.9  4.1  1.637 × 1015  306  52  −72  98  41  −112  273  75  24  5  0.72  5.6  7  8  0.06  2014  01 29  18:23:44.88  38.342  21.9804  8.47  3.1  3.3  1.31 × 1014  310  60  −66  88  38  −125  264  66  23  12  0.53  6.3  6  15  0.11  2014  01 30  23:48:14.98  38.3857  21.8672  9.04  3.7  3.7  4.311 × 1014  231  26  −132  96  71  −72  31  60  172  24  0.57  2.9  7  11  0.22  2014  02 04  18:19:32.44  38.3397  21.9749  8.94  3.4  3.5  2.501 × 1014  311  58  −57  81  45  −131  275  62  18  7  0.63  6.8  6  9  0.06  2014  02 04  22:49:01.50  38.3339  21.9769  8.67  3.9  3.9  7.897 × 1014  111  45  −93  296  45  −87  282  88  23  0  0.73  5.1  7  9  0.04  2014  02 07  01:21:53.22  38.3144  21.7066  16.29  4.3  4.2  2.221 × 1015  303  77  −41  44  51  −163  255  37  359  17  0.65  2.1  9  12  0.28  2014  02 12  07:41:01.26  37.9327  22.5926  11.70  3.5  3.5  2.315 × 1014  264  29  −109  105  63  −80  36  70  188  18  0.13  2.1  5  6  0.22  2014  02 28  22:13:55.08  38.1975  22.5207  8.14  3.5  3.7  3.920 × 1014  300  33  −63  88  61  −107  323  69  190  14  0.24  2.1  8  9  0.15  2014  03 21  18:35:49.92  38.4122  22.4547  10.21  4.0  3.9  7.537 × 1014  25  41  −171  288  84  −49  234  37  347  27  0.51  2.0  10  11  0.27  2014  04 07  20:15:11.86  38.3348  21.8022  9.29  3.2  3.3  1.01 × 1014  232  25  −140  105  74  −70  41  57  179  26  0.74  3.5  4  11  0.14  2014  04 10  17:40:45.16  37.9305  22.5980  10.47  3.5  3.5  2.577 × 1014  110  48  −78  273  43  −103  84  81  192  3  0.12  1.7  5  8  0.25  2014  04 17  07:04:04.56  38.4092  22.4625  9.57  3.7  3.8  5.569 × 1014  281  64  −56  44  42  −138  237  57  347  12  0.20  1.9  10  20  0.28  2014  04 18  05:07:36.93  38.4223  21.8443  11.25  4.2  3.9  7.888 × 1014  102  86  −72  204  18  −168  30  46  176  39  0.63  3.0  7  13  0.33  2014  05 10  03:04:50.13  38.4164  22.4471  9.99  4.2  4.1  1.889 × 1015  286  69  −64  53  33  −138  232  58  357  19  0.31  2.2  9  11  0.35  2014  05 11  17:34:06.24  38.4361  21.6997  15.02  3.6  3.6  2.879 × 1014  38  78  173  130  83  12  264  3  354  13  0.73  2.7  8  8  0.27  2014  06 08  15:10:51.81  38.3260  22.0525  4.30  4.3  4.2  2.506 × 1015  105  46  −84  276  45  −97  95  85  191  0  0.53  2.1  12  4  0.09  2014  06 10  02:14:30.72  38.3332  22.062  8.76  3.3  3.5  1.96 × 1014  95  46  −91  277  44  −89  328  89  186  1  0.30  2.5  8  7  0.14  2014  06 10  22:52:42.08  38.3315  22.0668  8.15  3.6  3.5  2.196 × 1014  272  57  −100  110  34  −75  154  76  9  12  0.51  2.2  5  12  0.18  2014  06 20  01:53:28.78  38.323  22.0492  8.32  3.3  3.4  1.754 × 1014  112  41  −90  291  49  −90  200  86  22  4  0.39  4.3  8  5  0.07  2014  06 25  09:21:41.85  38.3597  21.7543  17.93  4.2  4.1  1.605 × 1015  197  69  −136  88  50  −28  60  45  318  12  0.40  2.1  9  14  0.29  2014  06 27  00:47:23.63  38.3852  21.9995  9.44  3.0  3.2  8.258 × 1013  325  31  −53  104  66  −110  341  64  209  19  0.49  2.6  7  9  0.35  2014  07 30  07:56:35.32  38.3487  21.8156  9.74  3.4  3.4  1.877 × 1014  239  24  −125  97  70  −76  29  62  176  24  0.40  2.5  10  9  0.16  2014  08 09  22:22:24.28  38.3603  21.8744  8.51  3.0  3.0  4.529 × 1013  236  39  −120  93  57  −67  53  69  167  9  0.56  2.9  4  15  0.17  2014  08 12  04:06:16.20  38.3992  22.5064  10.05  3.4  3.4  1.462 × 1014  255  30  −101  87  60  −84  14  74  173  15  0.56  1.9  6  5  0.24  2014  08 28  04:11:12.25  38.4129  22.4655  10.62  3.3  3.4  1.451 × 1014  302  65  −61  69  38  −136  254  59  11  15  0.70  3.1  6  21  0.10  2014  09 03  00:58:47.98  38.3379  21.9031  6.85  3.5  3.8  5.454 × 1014  78  18  −91  259  72  −90  169  63  348  27  0.36  4.7  5  9  0.08  2014  09 19  09:33:24.85  38.3620  21.8255  8.76  3.5  3.7  4.038 × 1014  274  53  −65  56  44  −119  243  69  346  5  0.41  3.1  11  6  0.12  2014  09 19  15:35:08.84  38.3687  21.8372  10.27  4.1  4.1  1.619 × 1015  86  54  −88  262  37  −93  7  81  174  9  0.60  2.8  8  4  0.11  2014  09 21  00:43:39.42  38.3477  21.8381  9.50  4.6  4.8  1.780 × 1016  70  47  −102  268  44  −77  269  81  169  2  0.74  4.9  10  3  0.04  2014  09 21  01:13:26.45  38.3637  21.8235  9.25  4.0  4.3  3.008 × 1015  271  42  −78  74  49  −101  283  81  172  3  0.70  2.9  11  5  0.08  2014  09 25  02:04:24.34  38.3511  21.8079  10.52  3.7  3.9  9.637 × 1014  269  55  −82  76  35  −101  206  78  354  10  0.39  4.6  12  7  0.03  2014  09 26  04:33:32.17  38.3447  21.9647  9.38  3.8  3.9  8.386 × 1014  293  51  −73  88  41  −110  260  76  11  5  0.56  2.4  9  7  0.03  2014  10 30  06:09:09.20  38.1461  22.6267  9.18  3.7  3.9  8.056 × 1014  293  42  −70  87  51  −107  298  76  189  5  0.19  2.6  7  2  0.09  2014  11 07  17:12:59.68  38.2890  22.1226  8.51  4.8  4.9  3.261 × 1016  270  23  −96  96  67  −88  10  67  184  22  0.75  3.0  13  3  0.07  2014  12 09  17:08:29.00  38.4047  22.2319  14.68  3.6  3.5  1.890 × 1014  122  23  −94  307  67  −88  220  68  36  22  0.48  2.0  8  5  0.30                    Plane 1  Plane 2  P-axis  T-axis            Year  Date  Origin time  Latitude (°N)  Longitude (°E)  Depth (km)  ML  Mw  M (N m)  Strike (°)  Dip (°)  Rake (°)  Strike (°)  Dip (°)  Rake (°)  Trend (°)  Plunge (°)  Trend (°)  Plunge (°)  VR  CN  N  FMVAR  STVAR  2011  02 05  02:52:38.47  38.4179  22.0244  7.79  3.5  3.6  3.662 × 1014  307  70  −79  97  22  −118  234  63  28  25  0.18  3.4  7  8  0.12  2011  02 11  17:56:56.00  38.3932  21.7899  10.12  4.2  4.0  1.407 × 1015  129  90  −25  219  65  −180  81  17  176  17  0.70  2.1  10  9  0.24  2011  02 12  11:37:36.58  38.3897  21.7895  10.99  3.6  3.7  3.999 × 1014  224  71  168  319  78  20  91  5  183  22  0.32  1.9  9  10  0.23  2011  02 20  19:24:07.94  38.4991  21.6624  14.46  3.3  3.6  2.842 × 1014  75  72  −179  344  89  −18  298  14  31  12  0.50  2.3  8  8  0.24  2011  02 20  21:57:16.62  38.5002  21.6627  14.36  3.7  3.7  3.958 × 1014  341  85  −31  74  59  −174  293  25  31  18  0.54  2.3  9  9  0.23  2011  02 24  23:29:46.08  38.3904  21.8013  10.71  3.7  3.6  3.390 × 1014  126  59  −22  228  71  −147  91  36  355  7  0.27  3.0  7  21  0.33  2011  04 13  02:32:27.09  38.2667  22.1924  9.68  3.4  3.4  1.394 × 1014  269  19  84  83  71  −92  349  64  174  26  0.27  2.6  5  7  0.09  2011  05 04  12:39:42.86  38.2867  22.3976  13.27  4.0  3.8  6.153 × 1014  89  60  −88  264  31  −94  5  75  177  15  0.62  1.9  7  7  0.20  2011  05 04  14:35:15.76  38.3457  21.8141  9.90  3.6  3.4  1.881 × 1014  242  23  −140  114  75  −72  48  56  190  28  0.42  4.0  7  9  0.11  2011  06 06  11:06:01.57  38.4366  21.8307  13.09  3.4  3.4  1.672 × 1014  257  26  −106  94  65  −83  19  69  178  20  0.54  2.6  5  6  0.24  2011  06 07  23:39:15.06  38.4318  22.0633  6.55  3.3  3.2  7.355 × 1013  256  28  −83  68  63  −94  330  72  161  18  0.62  5.4  5  9  0.03  2011  07 18  03:58:51.62  38.2368  22.5373  19.19  3.3  3.3  9.813 × 1013  305  34  −54  83  63  −111  316  65  189  16  0.43  1.9  6  13  0.21  2012  07 16  20:26:48.44  38.3947  22.0013  9.64  3.1  3.3  1.161 × 1014  291  28  −79  99  63  −96  356  72  193  18  0.57  2.1  6  5  0.26  2012  08 16  21:22:54.36  38.2661  22.5302  14.40  3.5  3.7  4.153 × 1014  234  57  −131  111  50  −45  87  57  351  4  0.36  1.7  9  7  0.26  2012  09 08  16:40:14.70  38.3757  22.0631  10.59  3.7  3.5  2.456 × 1014  322  30  −56  104  66  −108  343  65  207  19  0.28  1.8  8  8  0.30  2012  09 19  00:55:36.94  38.351  22.3146  15.51  3.1  3.3  1.239 × 1014  299  31  −64  89  63  −105  330  69  190  17  0.53  1.9  4  9  0.28  2012  09 21  15:21:21.12  38.3534  22.0147  8.41  3.9  3.9  8.287 × 1014  292  23  −75  95  67  −96  354  67  190  22  0.59  1.9  10  7  0.20  2012  09 22  03:52:24.52  38.0740  22.7446  15.99  5.1  4.9  2.660 × 1016  300  21  −68  96  71  −98  353  63  193  25  0.60  1.7  12  8  0.29  2012  10 18  19:27:53.28  38.5509  21.9171  18.69  3.1  3.3  1.319 × 1014  238  48  −131  110  56  −54  77  61  175  4  0.44  1.9  5  4  0.22  2012  12 09  01:23:06.11  37.9479  22.6038  10.28  4.1  4.0  1.313 × 1015  271  30  −97  99  60  −86  19  75  186  15  0.46  1.8  9  5  0.21  2012  12 27  23:20:53.86  38.2181  21.8490  9.06  3.8  3.9  9.652 × 1014  255  35  −138  128  68  −63  76  58  198  18  0.80  2.0  10  13  0.26  2013  01 28  04:14:06.67  38.3250  22.1627  9.52  3.6  3.7  4.707 × 1014  277  27  −83  89  63  −94  351  72  182  18  0.54  2.1  12  11  0.21  2013  05 19  12:00:41.08  38.3916  21.7607  13.88  3.1  3.3  1.013 × 1014  203  46  −135  78  60  −54  40  58  143  8  0.27  2.4  8  11  0.23  2013  05 28  01:13:00.49  38.2261  22.1059  9.85  3.6  3.6  3.109 × 1014  287  42  −67  78  52  −109  290  74  181  5  0.44  2.7  9  8  0.17  2013  05 31  08:57:25.28  38.2293  22.1097  10.14  4.0  3.7  3.856 × 1014  226  26  −112  71  66  −79  0  67  153  20  0.44  2.2  10  5  0.23  2013  06 11  19:36:16.60  38.1590  23.1956  10.00  3.5  3.6  3.128 × 1014  252  26  −73  54  65  −98  307  69  150  20  0.36  1.8  8  10  0.25  2013  06 27  17:24:43.40  38.2169  22.1197  9.18  3.8  3.8  5.454 × 1014  103  48  −91  285  42  −89  358  87  194  3  0.53  2.0  7  8  0.24  2013  07 09  21:46:19.96  38.4156  21.9633  9.80  3.1  3.2  8.332 × 1013  282  26  −75  85  65  −97  340  70  181  19  0.44  3.0  6  13  0.27  2013  07 14  07:46:58.39  38.2298  22.0917  10.95  3.3  3.5  2.006 × 1014  256  40  −105  95  51  −78  57  79  176  5  0.85  3.2  5  24  0.22  2013  07 24  02:55:49.81  38.2298  22.0986  10.98  3.5  3.7  4.312 × 1014  263  39  −98  94  51  −83  41  82  179  6  0.70  2.1  9  6  0.16  2013  09 20  02:05:19.26  38.1670  23.1052  13.42  4.4  4.4  4.304 × 1015  56  47  −92  238  43  −88  301  87  147  2  0.34  2.0  11  6  0.25  2013  09 26  02:34:36.34  38.3019  22.1353  8.39  3.7  3.8  7.233 × 1014  261  25  −103  95  65  −84  17  69  181  20  0.81  2.5  6  6  0.13  2013  09 26  05:25:12.02  38.2999  22.1292  8.85  3.1  3.1  6.028 × 1013  246  21  −121  99  73  −79  26  61  180  27  0.40  2.5  5  12  0.21  2013  10 22  03:38:57.90  38.3669  21.8797  8.19  3.1  3.1  9.891 × 1013  131  59  −13  227  79  −148  93  30  355  13  0.76  2.7  6  13  0.22  2013  12 09  08:59:35.62  38.3807  21.7454  14.54  3.7  3.6  3.308 × 1014  64  47  −74  221  45  −106  47  78  143  1  0.54  1.7  7  6  0.19  2013  12 22  18:04:02.94  37.8548  22.7335  13.74  3.5  3.6  3.080 × 1014  293  36  −82  103  54  −96  349  80  197  9  0.23  1.4  6  5  0.29  2014  01 24  22:08:48.30  38.3374  21.9980  7.91  3.8  3.8  6.244 × 1014  311  49  −65  96  47  −115  291  72  24  1  0.48  3.6  9  9  0.09  2014  01 29  09:14:23.47  38.3411  21.9822  8.48  3.9  4.1  1.637 × 1015  306  52  −72  98  41  −112  273  75  24  5  0.72  5.6  7  8  0.06  2014  01 29  18:23:44.88  38.342  21.9804  8.47  3.1  3.3  1.31 × 1014  310  60  −66  88  38  −125  264  66  23  12  0.53  6.3  6  15  0.11  2014  01 30  23:48:14.98  38.3857  21.8672  9.04  3.7  3.7  4.311 × 1014  231  26  −132  96  71  −72  31  60  172  24  0.57  2.9  7  11  0.22  2014  02 04  18:19:32.44  38.3397  21.9749  8.94  3.4  3.5  2.501 × 1014  311  58  −57  81  45  −131  275  62  18  7  0.63  6.8  6  9  0.06  2014  02 04  22:49:01.50  38.3339  21.9769  8.67  3.9  3.9  7.897 × 1014  111  45  −93  296  45  −87  282  88  23  0  0.73  5.1  7  9  0.04  2014  02 07  01:21:53.22  38.3144  21.7066  16.29  4.3  4.2  2.221 × 1015  303  77  −41  44  51  −163  255  37  359  17  0.65  2.1  9  12  0.28  2014  02 12  07:41:01.26  37.9327  22.5926  11.70  3.5  3.5  2.315 × 1014  264  29  −109  105  63  −80  36  70  188  18  0.13  2.1  5  6  0.22  2014  02 28  22:13:55.08  38.1975  22.5207  8.14  3.5  3.7  3.920 × 1014  300  33  −63  88  61  −107  323  69  190  14  0.24  2.1  8  9  0.15  2014  03 21  18:35:49.92  38.4122  22.4547  10.21  4.0  3.9  7.537 × 1014  25  41  −171  288  84  −49  234  37  347  27  0.51  2.0  10  11  0.27  2014  04 07  20:15:11.86  38.3348  21.8022  9.29  3.2  3.3  1.01 × 1014  232  25  −140  105  74  −70  41  57  179  26  0.74  3.5  4  11  0.14  2014  04 10  17:40:45.16  37.9305  22.5980  10.47  3.5  3.5  2.577 × 1014  110  48  −78  273  43  −103  84  81  192  3  0.12  1.7  5  8  0.25  2014  04 17  07:04:04.56  38.4092  22.4625  9.57  3.7  3.8  5.569 × 1014  281  64  −56  44  42  −138  237  57  347  12  0.20  1.9  10  20  0.28  2014  04 18  05:07:36.93  38.4223  21.8443  11.25  4.2  3.9  7.888 × 1014  102  86  −72  204  18  −168  30  46  176  39  0.63  3.0  7  13  0.33  2014  05 10  03:04:50.13  38.4164  22.4471  9.99  4.2  4.1  1.889 × 1015  286  69  −64  53  33  −138  232  58  357  19  0.31  2.2  9  11  0.35  2014  05 11  17:34:06.24  38.4361  21.6997  15.02  3.6  3.6  2.879 × 1014  38  78  173  130  83  12  264  3  354  13  0.73  2.7  8  8  0.27  2014  06 08  15:10:51.81  38.3260  22.0525  4.30  4.3  4.2  2.506 × 1015  105  46  −84  276  45  −97  95  85  191  0  0.53  2.1  12  4  0.09  2014  06 10  02:14:30.72  38.3332  22.062  8.76  3.3  3.5  1.96 × 1014  95  46  −91  277  44  −89  328  89  186  1  0.30  2.5  8  7  0.14  2014  06 10  22:52:42.08  38.3315  22.0668  8.15  3.6  3.5  2.196 × 1014  272  57  −100  110  34  −75  154  76  9  12  0.51  2.2  5  12  0.18  2014  06 20  01:53:28.78  38.323  22.0492  8.32  3.3  3.4  1.754 × 1014  112  41  −90  291  49  −90  200  86  22  4  0.39  4.3  8  5  0.07  2014  06 25  09:21:41.85  38.3597  21.7543  17.93  4.2  4.1  1.605 × 1015  197  69  −136  88  50  −28  60  45  318  12  0.40  2.1  9  14  0.29  2014  06 27  00:47:23.63  38.3852  21.9995  9.44  3.0  3.2  8.258 × 1013  325  31  −53  104  66  −110  341  64  209  19  0.49  2.6  7  9  0.35  2014  07 30  07:56:35.32  38.3487  21.8156  9.74  3.4  3.4  1.877 × 1014  239  24  −125  97  70  −76  29  62  176  24  0.40  2.5  10  9  0.16  2014  08 09  22:22:24.28  38.3603  21.8744  8.51  3.0  3.0  4.529 × 1013  236  39  −120  93  57  −67  53  69  167  9  0.56  2.9  4  15  0.17  2014  08 12  04:06:16.20  38.3992  22.5064  10.05  3.4  3.4  1.462 × 1014  255  30  −101  87  60  −84  14  74  173  15  0.56  1.9  6  5  0.24  2014  08 28  04:11:12.25  38.4129  22.4655  10.62  3.3  3.4  1.451 × 1014  302  65  −61  69  38  −136  254  59  11  15  0.70  3.1  6  21  0.10  2014  09 03  00:58:47.98  38.3379  21.9031  6.85  3.5  3.8  5.454 × 1014  78  18  −91  259  72  −90  169  63  348  27  0.36  4.7  5  9  0.08  2014  09 19  09:33:24.85  38.3620  21.8255  8.76  3.5  3.7  4.038 × 1014  274  53  −65  56  44  −119  243  69  346  5  0.41  3.1  11  6  0.12  2014  09 19  15:35:08.84  38.3687  21.8372  10.27  4.1  4.1  1.619 × 1015  86  54  −88  262  37  −93  7  81  174  9  0.60  2.8  8  4  0.11  2014  09 21  00:43:39.42  38.3477  21.8381  9.50  4.6  4.8  1.780 × 1016  70  47  −102  268  44  −77  269  81  169  2  0.74  4.9  10  3  0.04  2014  09 21  01:13:26.45  38.3637  21.8235  9.25  4.0  4.3  3.008 × 1015  271  42  −78  74  49  −101  283  81  172  3  0.70  2.9  11  5  0.08  2014  09 25  02:04:24.34  38.3511  21.8079  10.52  3.7  3.9  9.637 × 1014  269  55  −82  76  35  −101  206  78  354  10  0.39  4.6  12  7  0.03  2014  09 26  04:33:32.17  38.3447  21.9647  9.38  3.8  3.9  8.386 × 1014  293  51  −73  88  41  −110  260  76  11  5  0.56  2.4  9  7  0.03  2014  10 30  06:09:09.20  38.1461  22.6267  9.18  3.7  3.9  8.056 × 1014  293  42  −70  87  51  −107  298  76  189  5  0.19  2.6  7  2  0.09  2014  11 07  17:12:59.68  38.2890  22.1226  8.51  4.8  4.9  3.261 × 1016  270  23  −96  96  67  −88  10  67  184  22  0.75  3.0  13  3  0.07  2014  12 09  17:08:29.00  38.4047  22.2319  14.68  3.6  3.5  1.890 × 1014  122  23  −94  307  67  −88  220  68  36  22  0.48  2.0  8  5  0.30  View Large APPENDIX B: CHARACTERISTICS OF EARTHQUAKES CLUSTERS Table B1. Characteristics of earthquakes clusters: serial number (ID), where W is for clusters that occurred on the western part of Corinth Gulf and E for those on the eastern part, start and end time, number of events (N), maximum magnitude in each cluster (Mmax), mean epicentral coordinates (Longitude and Latitude), mean depth of the segment, strike, dip, fault trace at the given depth, the subregion (see Table 2) and the absolute difference in strike (ΔS) and dip (ΔD) from the corresponding TSMT solution. ID  Start  End  N  Mmax  Longitude (°N)  Latitude (°E)  Depth (km)  Strike (°)  Dip (°)  Fault trace (°N, °E)  Subregion  ΔS (°)  ΔD (°)  W01  2008/07/19 00:21:22  2008/07/30 10:54:24  113  3.7  21.9046  38.2919  7  100  40  21.8887–21.9171, 38.2935–38.2874  02  24  8  W02  2009/01/10 13:31:41  2009/01/13 05:05:03  27  3.1  22.0364  38.3089  8  280  50  22.0235–22.0493, 38.3108–38.3067  03  3  23  W03  2009/03/10 00:18:42  2009/03/16 20:46:13  56  3.9  21.8442  38.3513  8.5  255  45  21.8301–21.8537, 38.3544–38.3590  02  8  5  W04  2009/06/23 10:11:21  2009/07/10 03:45:52  72  3.7  22.0621  38.3064  8  290  45  22.0390–22.0801, 38.3149–38.3006  03  13  18  W05  2010/05/06 10:08:17  2010/05/27 03:11:32  229  3.8  21.8318  38.4289  10  270  55  21.8178–21.8556, 38.4278  02  7  15  W06  2011/02/01 19:52:23  2011/02/03 17:58:56  19  3.5  21.7981  38.3903  10.5  270  50  21.7908–21.8037, 38.3920  02  7  10  W07  2011/02/04 11:05:46  2011/02/07 15:27:39  109  3.5  22.0236  38.4158  8.5  290  65  22.0127–22.0337, 38.4208–38.4140  03  13  38  W08  2011/02/19 19:04:32  2011/02/25 19:26:46  103  3.7  21.6590  38.4988  14.5  75  84  21.6513–21.6715, 38.4951–38.5024  01  12  8  W09  2011/03/19 03:33:33  2011/03/24 06:33:46  25  2.9  21.8636  38.3933  8.5  255  60  21.8487–21.8791, 38.392–38.398  02  8  17  W10  2011/07/23 10:20:18  2011/08/11 04:15:37  279  4.3  21.7514  38.3149  9  240  60  21.7371–21.7828, 38.3033–38.3249  02  23  17  W11  2011/08/30 05:09:32  2011/09/21 03:40:04  56  3.4  21.7599  38.3157  9.5  290  55  21.7452–21.7726, 38.3163–38.3098  02  17  12  W12  2011/09/18 05:43:49  2011/09/21 01:29:14  91  3.3  21.8316  38.2193  7.5  220  50  21.8252–21.8403, 38.2101–38.2253  02  43  7  W13  2011/10/01 21:06:19  2011/10/03 03:02:14  10  2.4  21.7653  38.3245  8.5  110  45  21.7589–21.7698, 38.3270–38.3227  02  34  3  W14  2011/10/04 18:28:25  2011/10/05 05:26:43  10  2.3  21.8300  38.2168  8  270  40  21.8259–21.8346, 38.2171  02  7  3  W15  2011/11/16 09:04:18  2011/11/20 00:15:24  40  2.2  21.8452  38.4131  10.5  270  50  21.8422–21.8551, 38.4140  02  7  7  W16  2011/11/30 03:16:36  2011/12/01 07:34:25  20  1.7  21.8826  38.2647  7.5  270  30  21.8775–21.8860, 38.2616  02  7  13  W17  2011/12/19 23:41:38  2011/12/22 12:22:22  25  2.3  22.0413  38.3417  8.5  280  65  22.0324–22.0454, 38.3422–38.3405  03  3  38  W18  2012/01/17 17:13:01  2012/01/21 22:15:16  62  3.1  21.8365  38.3795  9  270  65  21.8294–21.8474, 38.378  02  7  22  W19  2012/02/25 11:01:13  2012/02/27 00:53:16  11  2.3  22.0812  38.3126  8.5  290  60  22.0762–22.0804, 38.3126–38.3093  03  13  33  W20  2012/03/11 23:49:25  2012/03/24 05:44:52  37  2.8  21.6914  38.5893  10  110  30  21.690–21.7008, 38.5903–38.585  02  34  18  W21  2012/04/15 21:03:53  2012/04/24 17:07:35  91  3.8  22.1226  38.2934  8.0  280  60  22.1059–22.1318, 38.296–38.2908  03  3  33  W22  2012/06/12 08:34:06  2012/06/14 03:08:59  23  2.1  22.0666  38.2721  10.5  110  55  22.0596–22.0705, 38.2720–38.2685  03  17  8  W23  2012/06/21 15:37:15  2012/06/28 22:24:51  18  2.9  22.0951  38.3029  8.0  290  55  22.0822–22.0992, 38.3123– 38.3005  03  13  28  W24  2012/06/24 02:14:30  2012/06/27 20:42:11  15  1.7  21.8633  38.4957  15  90  40  21.8614–21.8700, 38.4933  02  14  8  W25  2012/08/12 08:07:46  2012/08/23 18:40:45  64  3.1  22.1127  38.2953  8.25  280  60  22.1004–22.1356, 38.2977–38.290  03  3  33  W26  2012/09/06 01:43:47  2012/09/18 02:03:35  32  3.1  21.8616  38.3603  8.7  290  50  21.8577–21.8757, 38.362–38.358  02  27  7  W27  2013/01/27 15:47:35  2013/01/30 11:44:12  30  3.2  38.3017  23.1105  8.5  290  60  22.1363–22.1563, 38.3239–38.3160  03  13  33  W28  2013/01/28 08:43:15  2013/02/14 13:09:31  44  3.6  22.1469  38.3173  8.5  290  60  22.1018–22.1200, 38.3066–38.2988  03  13  33  W29  2013/03/20 22:41:31  2013/03/24 18:27:53  23  3.3  22.0391  38.3229  8.0  280  40  22.0302–22.0448, 38.3217–38.3200  03  3  13  W30  2013/06/14 21:09:36  2013/06/19 05:52:13  71  1.9  22.1730  38.2420  8.5  260  45  22.1594–22.1913, 38.2382–38.2441  04  11  9  W31  2013/07/05 17:23:49  2013/07/07 10:15:56  53  2.7  22.0629  38.3277  8.5  90  50  22.0497–22.0686, 38.3268  03  3  13  W32  2013/09/09 16:26:48  2013/09/14 00:00:09  131  2.8  22.0326  38.3984  8  110  50  22.0215–22.0395, 38.4011–38.3952  03  17  13  W33  2013/10/22 03:38:57  2013/10/29 23:06:54  29  3.1  21.8812  38.3682  7.5  110  30  21.8909–21.9045, 38.3753–38.3710  02  34  18  W34  2013/10/26 09:26:47  2013/11/12 12:25:18  249  3.1  22.1119  38.2331  10.5  280  45  22.1036–22.1209, 38.2328–38.2307  04  9  9  W35  2013/10/26 09:33:11  2013/10/28 11:27:31  22  3.1  21.8983  38.3753  8  110  40  21.8718–21.8854, 38.3689–38.3641  02  34  8  W36  2013/12/02 21:02:46  2013/12/15 18:27:06  79  2.8  21.8422  38.3267  8  270  60  21.820–21.860, 38.328  02  7  17  W37  2014/01/07 23:41:30  2014/01/22 06:09:05  53  2.9  22.0175  38.3872  7.5  280  60  22.0133–22.0251, 38.3885–38.3862  03  3  33  W38  2014/01/16 22:53:58  2014/01/26 07:49:42  37  2.6  21.9802  38.3465  8.25  280  40  21.9653–21.9880, 38.3495–38.3459  03  3  13  W39  2014/06/08 00:32:41  2014/06/24 19:34:06  132  4.3  22.0545  38.3221  8.5  280  50  22.0441–22.0627, 38.3248–38.3216  03  3  23  W40  2014/06/08 16:49:41  2014/06/17 13:30:32  67  3.6  22.0645  38.3328  8.5  270  50  22.0524–22.0731, 38.3313  03  7  23  W41  2014/07/25 09:56:50  2014/07/29 06:08:57  13  2.2  22.0862  38.3013  8.5  280  50  22.0808–22.0931, 38.3021–38.3005  03  3  23  W42  2014/08/23 21:00:15  2014/08/27 21:47:26  18  2.4  22.0749  38.3079  8.5  280  45  22.0683–22.0791, 38.3107–38.3090  03  3  18  W43  2014/09/18 05:43:21  2014/09/28 23:34:54  170  4.6  21.8181  38.3573  10  250  55  21.796–21.8551, 38.349–38.36  02  13  12  W44  2014/11/07 17:12:59  2014/12/02 00:33:13  270  4.8  22.1380  38.2745  7.5  270  35  22.12–22.16, 38.275  03  7  8  W45  2014/11/24 12:32:39  2014/11/27 04:52:27  14  2.5  22.0902  38.3046  8.5  270  45  22.0765–22.0960, 38.3039–38.3005  03  7  18  W46  2014/12/09 14:06:05  2014/12/15 02:27:30  22  2.2  22.0705  38.3035  8.0  290  40  22.052–22.0762, 38.3052–38.2930  03  13  13  W47  2014/12/17 18:20:15  2014/12/24 22:09:10  28  2.1  22.0817  38.2991  8.25  280  50  22.0770–22.0967, 38.3005–38.2971  03  3  23  E01  2009/05/16 12:56:19  2009/05/22 17:13:19  43  4.4  22.6764  38.1230  9.0  280  50  22.6542–22.7014, 38.1245–38.1143  06  18  23  E02  2013/06/10 04:53:57  2013/06/29 02:55:05  332  3.5  23.1999  38.1615  8.0  60  55  23.1896–23.2193, 38.1484–38.1606  08  4  7  ID  Start  End  N  Mmax  Longitude (°N)  Latitude (°E)  Depth (km)  Strike (°)  Dip (°)  Fault trace (°N, °E)  Subregion  ΔS (°)  ΔD (°)  W01  2008/07/19 00:21:22  2008/07/30 10:54:24  113  3.7  21.9046  38.2919  7  100  40  21.8887–21.9171, 38.2935–38.2874  02  24  8  W02  2009/01/10 13:31:41  2009/01/13 05:05:03  27  3.1  22.0364  38.3089  8  280  50  22.0235–22.0493, 38.3108–38.3067  03  3  23  W03  2009/03/10 00:18:42  2009/03/16 20:46:13  56  3.9  21.8442  38.3513  8.5  255  45  21.8301–21.8537, 38.3544–38.3590  02  8  5  W04  2009/06/23 10:11:21  2009/07/10 03:45:52  72  3.7  22.0621  38.3064  8  290  45  22.0390–22.0801, 38.3149–38.3006  03  13  18  W05  2010/05/06 10:08:17  2010/05/27 03:11:32  229  3.8  21.8318  38.4289  10  270  55  21.8178–21.8556, 38.4278  02  7  15  W06  2011/02/01 19:52:23  2011/02/03 17:58:56  19  3.5  21.7981  38.3903  10.5  270  50  21.7908–21.8037, 38.3920  02  7  10  W07  2011/02/04 11:05:46  2011/02/07 15:27:39  109  3.5  22.0236  38.4158  8.5  290  65  22.0127–22.0337, 38.4208–38.4140  03  13  38  W08  2011/02/19 19:04:32  2011/02/25 19:26:46  103  3.7  21.6590  38.4988  14.5  75  84  21.6513–21.6715, 38.4951–38.5024  01  12  8  W09  2011/03/19 03:33:33  2011/03/24 06:33:46  25  2.9  21.8636  38.3933  8.5  255  60  21.8487–21.8791, 38.392–38.398  02  8  17  W10  2011/07/23 10:20:18  2011/08/11 04:15:37  279  4.3  21.7514  38.3149  9  240  60  21.7371–21.7828, 38.3033–38.3249  02  23  17  W11  2011/08/30 05:09:32  2011/09/21 03:40:04  56  3.4  21.7599  38.3157  9.5  290  55  21.7452–21.7726, 38.3163–38.3098  02  17  12  W12  2011/09/18 05:43:49  2011/09/21 01:29:14  91  3.3  21.8316  38.2193  7.5  220  50  21.8252–21.8403, 38.2101–38.2253  02  43  7  W13  2011/10/01 21:06:19  2011/10/03 03:02:14  10  2.4  21.7653  38.3245  8.5  110  45  21.7589–21.7698, 38.3270–38.3227  02  34  3  W14  2011/10/04 18:28:25  2011/10/05 05:26:43  10  2.3  21.8300  38.2168  8  270  40  21.8259–21.8346, 38.2171  02  7  3  W15  2011/11/16 09:04:18  2011/11/20 00:15:24  40  2.2  21.8452  38.4131  10.5  270  50  21.8422–21.8551, 38.4140  02  7  7  W16  2011/11/30 03:16:36  2011/12/01 07:34:25  20  1.7  21.8826  38.2647  7.5  270  30  21.8775–21.8860, 38.2616  02  7  13  W17  2011/12/19 23:41:38  2011/12/22 12:22:22  25  2.3  22.0413  38.3417  8.5  280  65  22.0324–22.0454, 38.3422–38.3405  03  3  38  W18  2012/01/17 17:13:01  2012/01/21 22:15:16  62  3.1  21.8365  38.3795  9  270  65  21.8294–21.8474, 38.378  02  7  22  W19  2012/02/25 11:01:13  2012/02/27 00:53:16  11  2.3  22.0812  38.3126  8.5  290  60  22.0762–22.0804, 38.3126–38.3093  03  13  33  W20  2012/03/11 23:49:25  2012/03/24 05:44:52  37  2.8  21.6914  38.5893  10  110  30  21.690–21.7008, 38.5903–38.585  02  34  18  W21  2012/04/15 21:03:53  2012/04/24 17:07:35  91  3.8  22.1226  38.2934  8.0  280  60  22.1059–22.1318, 38.296–38.2908  03  3  33  W22  2012/06/12 08:34:06  2012/06/14 03:08:59  23  2.1  22.0666  38.2721  10.5  110  55  22.0596–22.0705, 38.2720–38.2685  03  17  8  W23  2012/06/21 15:37:15  2012/06/28 22:24:51  18  2.9  22.0951  38.3029  8.0  290  55  22.0822–22.0992, 38.3123– 38.3005  03  13  28  W24  2012/06/24 02:14:30  2012/06/27 20:42:11  15  1.7  21.8633  38.4957  15  90  40  21.8614–21.8700, 38.4933  02  14  8  W25  2012/08/12 08:07:46  2012/08/23 18:40:45  64  3.1  22.1127  38.2953  8.25  280  60  22.1004–22.1356, 38.2977–38.290  03  3  33  W26  2012/09/06 01:43:47  2012/09/18 02:03:35  32  3.1  21.8616  38.3603  8.7  290  50  21.8577–21.8757, 38.362–38.358  02  27  7  W27  2013/01/27 15:47:35  2013/01/30 11:44:12  30  3.2  38.3017  23.1105  8.5  290  60  22.1363–22.1563, 38.3239–38.3160  03  13  33  W28  2013/01/28 08:43:15  2013/02/14 13:09:31  44  3.6  22.1469  38.3173  8.5  290  60  22.1018–22.1200, 38.3066–38.2988  03  13  33  W29  2013/03/20 22:41:31  2013/03/24 18:27:53  23  3.3  22.0391  38.3229  8.0  280  40  22.0302–22.0448, 38.3217–38.3200  03  3  13  W30  2013/06/14 21:09:36  2013/06/19 05:52:13  71  1.9  22.1730  38.2420  8.5  260  45  22.1594–22.1913, 38.2382–38.2441  04  11  9  W31  2013/07/05 17:23:49  2013/07/07 10:15:56  53  2.7  22.0629  38.3277  8.5  90  50  22.0497–22.0686, 38.3268  03  3  13  W32  2013/09/09 16:26:48  2013/09/14 00:00:09  131  2.8  22.0326  38.3984  8  110  50  22.0215–22.0395, 38.4011–38.3952  03  17  13  W33  2013/10/22 03:38:57  2013/10/29 23:06:54  29  3.1  21.8812  38.3682  7.5  110  30  21.8909–21.9045, 38.3753–38.3710  02  34  18  W34  2013/10/26 09:26:47  2013/11/12 12:25:18  249  3.1  22.1119  38.2331  10.5  280  45  22.1036–22.1209, 38.2328–38.2307  04  9  9  W35  2013/10/26 09:33:11  2013/10/28 11:27:31  22  3.1  21.8983  38.3753  8  110  40  21.8718–21.8854, 38.3689–38.3641  02  34  8  W36  2013/12/02 21:02:46  2013/12/15 18:27:06  79  2.8  21.8422  38.3267  8  270  60  21.820–21.860, 38.328  02  7  17  W37  2014/01/07 23:41:30  2014/01/22 06:09:05  53  2.9  22.0175  38.3872  7.5  280  60  22.0133–22.0251, 38.3885–38.3862  03  3  33  W38  2014/01/16 22:53:58  2014/01/26 07:49:42  37  2.6  21.9802  38.3465  8.25  280  40  21.9653–21.9880, 38.3495–38.3459  03  3  13  W39  2014/06/08 00:32:41  2014/06/24 19:34:06  132  4.3  22.0545  38.3221  8.5  280  50  22.0441–22.0627, 38.3248–38.3216  03  3  23  W40  2014/06/08 16:49:41  2014/06/17 13:30:32  67  3.6  22.0645  38.3328  8.5  270  50  22.0524–22.0731, 38.3313  03  7  23  W41  2014/07/25 09:56:50  2014/07/29 06:08:57  13  2.2  22.0862  38.3013  8.5  280  50  22.0808–22.0931, 38.3021–38.3005  03  3  23  W42  2014/08/23 21:00:15  2014/08/27 21:47:26  18  2.4  22.0749  38.3079  8.5  280  45  22.0683–22.0791, 38.3107–38.3090  03  3  18  W43  2014/09/18 05:43:21  2014/09/28 23:34:54  170  4.6  21.8181  38.3573  10  250  55  21.796–21.8551, 38.349–38.36  02  13  12  W44  2014/11/07 17:12:59  2014/12/02 00:33:13  270  4.8  22.1380  38.2745  7.5  270  35  22.12–22.16, 38.275  03  7  8  W45  2014/11/24 12:32:39  2014/11/27 04:52:27  14  2.5  22.0902  38.3046  8.5  270  45  22.0765–22.0960, 38.3039–38.3005  03  7  18  W46  2014/12/09 14:06:05  2014/12/15 02:27:30  22  2.2  22.0705  38.3035  8.0  290  40  22.052–22.0762, 38.3052–38.2930  03  13  13  W47  2014/12/17 18:20:15  2014/12/24 22:09:10  28  2.1  22.0817  38.2991  8.25  280  50  22.0770–22.0967, 38.3005–38.2971  03  3  23  E01  2009/05/16 12:56:19  2009/05/22 17:13:19  43  4.4  22.6764  38.1230  9.0  280  50  22.6542–22.7014, 38.1245–38.1143  06  18  23  E02  2013/06/10 04:53:57  2013/06/29 02:55:05  332  3.5  23.1999  38.1615  8.0  60  55  23.1896–23.2193, 38.1484–38.1606  08  4  7  View Large APPENDIX C: SPATIAL DISTRIBUTION OF ERRORS Figure C1. View largeDownload slide Spatial distribution of errors in (a) and (b) X, (c) and (d) Y and (e) and (f) Z-direction for the different parts of Corinth Gulf. Errors are in metres. Figure C1. View largeDownload slide Spatial distribution of errors in (a) and (b) X, (c) and (d) Y and (e) and (f) Z-direction for the different parts of Corinth Gulf. Errors are in metres. © The Author(s) 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

Relocation of recent seismicity and seismotectonic properties in the Gulf of Corinth (Greece)

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The Royal Astronomical Society
Copyright
© The Author(s) 2017. Published by Oxford University Press on behalf of The Royal Astronomical Society.
ISSN
0956-540X
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1365-246X
D.O.I.
10.1093/gji/ggx450
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Abstract

Summary Recent seismicity (2008–2014) taking place in the Gulf of Corinth and recorded, since the establishment of the Hellenic Unified Seismological Network is relocated in this study. All the available P and S manually picked phases along with the waveforms of 55 broad-band, three-component seismological stations were used. The relocation is performed using the double difference method with differential times derived from phase-picked data and waveform cross-correlation. The accuracy of the relocated catalogue, estimated using a bootstrap approach, is of the order of few hundred metres. In an attempt to define the stress regime in the area, we compute moment tensors of 72 earthquakes with ML ≥ 3.0 and use them to calculate the total seismic moment tensor. A dominant strike of 270° that found in the westernmost part, was changed to 270°–290° at the centre of the gulf, perpendicular to the almost N–S extension of the rift. Further to the east, a gradual change in fault orientation is observed. In the easternmost part, the strike becomes 240°, in agreement with the geometry of the rift. The highly accurate earthquake catalogue, consisting of ∼26 000 events, reveals two patterns of activity in the western Corinth Gulf, namely, strongly clustered seismicity in both space and time in shallow depths and below that activity a very narrow shallow north-dipping seismic zone. Earthquake clusters, mainly located in the western study area, are identified using CURATE algorithm and associated with different north or south-dipping fault segments. The seismicity in the shallow north-dipping seismic zone, defined in detail in this study, is continuous and free of earthquake clusters. This continuous activity most probably defines the boundaries between brittle and ductile layers. The central and eastern parts of the study area mainly accommodate spatiotemporal clusters. Waveform inversion, Seismicity and tectonics, Continental tectonics: extensional, Dynamics: seismotectonics 1 INTRODUCTION The Corinth Gulf (Fig. 1), located in central Greece, is one of the most seismically active areas in Europe (Papazachos & Papazachou 2003; Ambraseys 2009). Its overall shape is an asymmetric half-graben, trending WNW–ESE with its width increasing from a minimum in westernmost part (Psathopyrgos fault, Fig. 1) to a maximum in the central part (Xylokastro fault, Fig. 1; Armijo et al.1996). Geodetic measurements have shown that the extension rate is different in the two parts of the gulf (Billiris et al.1991; Clarke et al.1998; Briole et al.2000; Avallone et al.2004; Chousianitis et al.2015). The western part extends at a rate of 13–14 mm yr−1, with the largest opening rate measured near Aigio fault (Fig. 1, Briole et al.2000). The eastern part is deforming with lower extension rate of approximately 10–12 mm yr−1. Figure 1. View largeDownload slide Morphological map of the Corinth Gulf along with fault segments of: 01—Psathopyrgos, 02—Aigion, 03—Heliki, 04—Offshore Akrata, 05—Xylokastro, 06—Offshore Perachora, 07—Skinos, 08—Alepochori, 09—Kaparelli, 10—Lidoriki, 11—Delphi, 12—Trichonida and 13—Achaia (Armijo et al.1996; Kiratzi et al.2008; Console et al.2013; Karakostas et al.2017). Earthquakes that occurred since 1900 with M ≥ 6.0 and depth ≤ 50 km are shown by stars (Papazachos & Papazachou 2003). Red circles show earthquakes that occurred between 2008 and 2014 and were relocated in this study, whereas green circles show the relocated catalogue of Karakostas et al. (2017). The stations of the Hellenic Unified Seismological Network (HUSN) are displayed by triangles. Inset map: the backarc Aegean sea and the surrounded area, with the dominant seismotectonic features, including the Hellenic trench along with the subduction of the East Mediterranean lithosphere under the Aegean, and the North Anatolian Fault (NAF) which accommodates the westward extrusion of the Anatolian plate into the Aegean. The tectonic setting is supplemented with the existence of the Cephalonia (CTF) and Rhodes (RTF) transform faults. The study area is enclosed in the rectangle. Figure 1. View largeDownload slide Morphological map of the Corinth Gulf along with fault segments of: 01—Psathopyrgos, 02—Aigion, 03—Heliki, 04—Offshore Akrata, 05—Xylokastro, 06—Offshore Perachora, 07—Skinos, 08—Alepochori, 09—Kaparelli, 10—Lidoriki, 11—Delphi, 12—Trichonida and 13—Achaia (Armijo et al.1996; Kiratzi et al.2008; Console et al.2013; Karakostas et al.2017). Earthquakes that occurred since 1900 with M ≥ 6.0 and depth ≤ 50 km are shown by stars (Papazachos & Papazachou 2003). Red circles show earthquakes that occurred between 2008 and 2014 and were relocated in this study, whereas green circles show the relocated catalogue of Karakostas et al. (2017). The stations of the Hellenic Unified Seismological Network (HUSN) are displayed by triangles. Inset map: the backarc Aegean sea and the surrounded area, with the dominant seismotectonic features, including the Hellenic trench along with the subduction of the East Mediterranean lithosphere under the Aegean, and the North Anatolian Fault (NAF) which accommodates the westward extrusion of the Anatolian plate into the Aegean. The tectonic setting is supplemented with the existence of the Cephalonia (CTF) and Rhodes (RTF) transform faults. The study area is enclosed in the rectangle. The Corinth Gulf is bounded to the south by a series of major north-dipping normal faults and a few south-dipping ones at its northern part (Fig. 1). The south faults are, from west to east, the Psathopyrgos, Aigion, Heliki and Xylokastro faults (Fig. 1), with lengths between 15 and 25 km, an average strike of 270°–285° and a northward dip of about 50° near surface (Armijo et al.1996). At the eastern extremity of the gulf, the main fault segments (Offshore Perachora, Skinos and Alepochori, Fig. 1) strike at 250°–270°. Fault plane solutions presented by several researchers (Jackson et al.1982; Taymaz et al.1991; Baker et al.1997; Papazachos et al.1998) support the aforementioned strike and faulting type, in consistency with the rift structure. The west edge of the rift is connected with two major strike-slip faults, north and south of it (Fig. 1). The first one (12 in Fig. 1) is a left-lateral strike-slip fault located near Lake Trichonida, associated with the 1975 M = 6.0 earthquake (Kiratzi et al.2008). The second one (13 in Fig. 1) is a right-lateral strike-slip fault related to the 2008 M = 6.4 Achaia earthquake south of Patraikos Gulf (e.g. Serpetsidaki et al.2014; Karakostas et al.2017). Several destructive earthquakes struck the study area both in historical and instrumental eras (e.g. Papazachos & Papazachou 2003; Ambraseys 2009; Makropoulos et al.2012), with 10 of them with M ≥ 6.0 since 1900 (Fig. 1, Papazachos & Papazachou 2003). Several attempts to record the intense microseismicity in the study area were made in the past three decades. In 1991, a local network consisted of 51 seismological stations was installed in the western Corinth Gulf and operated for two months (Rigo et al.1996; Latorre et al.2004). During the summer of 1993, a temporary seismological network was installed over a period of seven weeks around the eastern Corinth Gulf (Hatzfeld et al.2000). Since 2000, the Corinth Rift Laboratory (CRL) has been in operation in the western part of Corinth Gulf (Lyon-Caen et al.2004; Bernard et al.2006; Lambotte et al.2014). Since 2008, permanent stations of the Hellenic Unified Seismological Network (HUSN) have been in continuous operation with adequate density for microseismicity monitoring and investigation (Fig. 1). The adequate coverage of the seismological networks secures the record of the frequent seismic excitations since 2000. The 2001 Agios Ioannis earthquake swarm took place in the southern part of the study area and was attributed to fluid-driven seismicity (Pacchiani & Lyon-Caen 2010). The next two seismic crises were originated offshore in 2003–2004 and 2006–2007, and for the first one evidence is provided that was related to fluid diffusion process (Bourouis & Cornet 2009; Duverger et al.2015). On 2007 April 08, the Trichonida earthquake swarm initiated near the area where the 1975 M = 6.0 earthquake occurred (Evangelidis et al.2008; Kiratzi et al.2008; Kassaras et al.2014). On 2010 January 18, an earthquake doublet occurred near Efpalio beneath the north coasts of the westernmost part of Corinth Gulf with two Mw = 5.5 events (Karakostas et al.2012; Sokos et al.2012; Ganas et al.2013). On 2013 May 22, an earthquake swarm that initiated near Aigio, with more than 1500 earthquakes detected in three months (Chouliaras et al.2015; Kapetanidis et al.2015; Mesimeri et al.2016; Kaviris et al.2017). The underlying mechanism responsible for the high seismic activity is still under question even though several studies were conducted by different research groups (e.g. Rigo et al.1996; Sorel 2000; Sachpazi et al.2003; Bell et al.2008, 2009; Taylor et al.2011; Godano et al.2014; Lambotte et al.2014; Beckers et al.2015). An outstanding feature revealed from the microseismicity in the area of western Corinth Gulf is the very shallow north-dipping seismic zone. Rigo et al. (1996) observed microseismicity defining the shallow north-dipping seismic zone and interpreted it as a hypothetical detachment zone on which the mapped north-dipping normal faults are rooting. Similar observations have been made since the operation of the CRL network (Lyon-Caen et al.2004; Bernard et al.2006; Lambotte et al.2014). Lambotte et al. (2014), in particular, identified several multiplets that match the geometry of the shallow north-dipping seismic zone. The fault plane solutions of these multiplets also advocate this seismic zone (Godano et al.2014). Lambotte et al. (2014) and Godano et al. (2014) relate the shallow north-dipping seismic zone with the existence of an immature detachment that is currently under development. On the contrary, Hatzfeld et al. (2000) proposed that the seismicity is probably related to the seismic–aseismic transition. A seismic reflection study conducted by Bell et al. (2008) suggests that the shallow geometry is more easily reconciled with a model in which faults are steep to a brittle–ductile transition, at 8–10 km, in agreement with the proposed model by Hatzfeld et al. (2000). Bell et al. (2008) found no evidence of fault listricity in shallower depths, and concluded that the existence of dominant south-dipping faults in their data is incompatible with a low angle north-dipping detachment. In this study, we compiled, for the first time, a highly accurate earthquake catalogue for the entire area of the Corinth Gulf, aiming to contribute to the discussion on the structures governing the seismogenic process. The relocation was performed considering seven years of seismicity (2008–2014) and using differential times from waveform cross-correlation and phase-picked data. We further attempt to interpret the seismotectonic regime in the study area, by combining the relocated earthquake catalogue along with fault plane solutions computed in this study. The contribution to the seismic hazard assessment is the identification of the earthquake clusters and their association with certain fault patches. These fault patches are then compared to the geometry of the major faults for investigating a possible correlation between the occurrence of strong earthquakes and earthquake clusters. The earthquake clusters were also compared with the background seismicity looking for possible patterns in the spatial distribution of earthquakes. 2 EARTHQUAKE RELOCATION PROCEDURE 2.1 Data All the available data (i.e. P, S phases and waveforms) of seven years (2008–2014) seismic activity in the study area are selected. Phases are gathered from the Geophysics Department of the Aristotle University of Thessaloniki (GD-AUTh, http://geophysics.geo.auth.gr/ss/) and the Geodynamics Institute of the National Observatory of Athens (NOA, http://bbnet.gein.noa.gr/HL/). Due to technical reasons, phases from NOA were also collected from the Euro-Mediterranean Seismological Center (http://www.emsc-csem.org/) where they are available in the appropriate format (Godey et al.2006). Then, we merged the bulletins and an initial earthquake catalogue was compiled, containing approximately 24 500 events for the western and 5300 events for the eastern part of the gulf. Regarding the waveforms, the recordings of the HUSN, which is in operation since 2008, are used. Particularly, we selected all the available recordings of 55 broad-band seismological stations with a sampling rate of 100 samples s−1. These recordings were archived in calendar order (approximately 3 TB) and used for the waveform cross-correlation process. Fig. 2 shows the distribution of the P and S phases with the epicentral distances in each subarea. For the western part, where the network is denser, 60 per cent and 93 per cent of the P, and 68 per cent and 96 per cent of the S phases are recorded in stations within distances of 50 and 100 km, respectively. In the eastern part, we observe that 66 per cent and 86 per cent of P, and 75 per cent and 90 per cent of S phases are recorded in distances up to 75 and 100 km, respectively. Figure 2. View largeDownload slide Number of P and S phases against epicentral distance (a) for western and (b) eastern Corinth Rift, respectively. Figure 2. View largeDownload slide Number of P and S phases against epicentral distance (a) for western and (b) eastern Corinth Rift, respectively. 2.2 Relocation process Due to differences in spatial distribution of seismicity, earthquake relocation was performed for each data set separately (western and eastern parts of the study area). For the initial earthquake location, we used the HYPOINVERSE (Klein 2002) software and all the available manually picked P and S phases. The inputs required in this software are a Vp/Vs ratio and an appropriate local velocity model. For defining the Vp/Vs ratio, we applied the Wadati method to two data sets consisting of 411 and 136 earthquakes with more than 20 S phases for each subarea. The resulting Vp/Vs ratio equals to 1.79 and 1.76 for the western and eastern parts, respectively. The 1-D local velocity model used for both subareas (Rigo et al.1996), after testing several crustal models, does not account for lateral variations in the velocity structure. Thus, an important factor in the location is the consideration of station corrections, which improve the performance of the velocity model. Station delays should be carefully calculated especially in large areas, where different type of phases are observed (Pg, Pb and Pn). In our case, it is not possible to calculate stations corrections for all the events simultaneously due to their relatively large interevent distance and the possible mix up of different P phases. For that reason, the two subareas are further divided into smaller parts, based on the spatial distribution of the seismicity. Stations residuals were calculated using HYPOINVERSE software and data sets consisting of the most recent events (2013–2014). After locating the earthquakes with HYPOINVERSE, we calculated a mean residual from all the available P phases and for each station. Then, we locate again the earthquakes taking into account the mean residual for each station and repeat the calculations until the changes in mean values in each station are negligible (Karakostas et al.2012, 2014). The selected data sets include almost all the stations used in this study, as they were gradually added to the network over the years. For a few stations that were not in operation at that time, the corrections were separately calculated. The obtained delays were used for locating all the earthquakes and the resulting solutions are used as input in the double difference method. In order to further improve the obtained locations, we relocate the earthquakes using the double difference package hypoDD (Waldhauser & Ellsworth 2000; Waldhauser 2001). Initially, we computed traveltime differences between the manually picked events in the catalogue, after choosing a maximum number of 10 neighbours per event within a 10 km distance. The event pairs with at least eight observations were kept, since the number of unknowns for one pair of events is eight and a maximum number of observations in each event pair was set equal to 40. This resulted to one million P phase pairs and 740 000 S phases pairs for the western part and 230 000 P phase pairs and 145 000 S phase pairs for the eastern part. An important factor in the application of hypoDD is the determination of the maximum interevent distance between pairs of events. It has been shown that the traveltime error increases with increasing interevent distance (e.g. Waldhauser & Ellsworth 2000; Waldhauser & Schaff 2008). For the phase-picked data, this is mainly caused by heterogeneities in the velocity structure. Considering this effect, we tested several values for maximum separation distance for the two areas. In Fig. 3, the median traveltime residuals are plotted as a function of binned interevent distance for the western and eastern subareas, respectively. The residuals become unstable (i.e. deviation from zero) with increasing distance, which is illustrated in distances greater than 5 km for the western and 6 km for the eastern subarea. These values are used as the maximum distance between linked events in the application of hypoDD for the phase-picked differential times. Figure 3. View largeDownload slide Median residuals against offset in 100 m bins for (a) and (b) phase-picked data and (c) and (d) cross-correlation data for the different parts of the Corinth Gulf. Figure 3. View largeDownload slide Median residuals against offset in 100 m bins for (a) and (b) phase-picked data and (c) and (d) cross-correlation data for the different parts of the Corinth Gulf. The relocated earthquakes obtained from the hypoDD application, using phase-picked data, are considered for preparing the waveforms for the cross-correlation process. Waveforms with 60 s duration, starting from the origin time of each event, were selected and archived by station in calendar order. The resulting database consists of several millions of waveforms for each subarea (∼65 GB). Then, the waveforms were bandpass filtered [2–10 Hz] and updated for P and S phase picks, when available. Cross-correlation measurements were performed in the time domain for all possible event pairs using 1 and 2 s window lengths for both P and S wave trains (Schaff et al.2004; Schaff & Waldhauser 2005). A lag search over ± 1 s was set in order to find the highest value of the correlation coefficient (CC), even if the seismic phases are misidentified. All event pairs with CC above 0.7 (70 per cent) were saved separately for each component, window length and subarea, resulting to several millions of correlation measurements. In order to prepare a robust data set of the acquired correlation measurements and reduce possible outliers, we applied the following restrictions. First, we considered only the event pairs with high similarity, namely CC ≥ 0.8 (80 per cent). Then, we looked for consistency of the measurements made in different window lengths (1 and 2 s). Therefore, we kept delay times based on the 1 s window length, if differences between same event pairs at the different windows are less than the sampling rate (0.01 s). Although all phases were manually picked and no theoretical times were calculated, we used this restriction to avoid bias from the routine analysis and possible misidentification of P and/or S phases. Finally, we selected event pairs with at least 4P or 4S delay time measurements. For the sake of comparison, we used only the differential times derived from waveform cross-correlation and relocated the events with hypoDD. Figs 3(c) and (d) shows that the median of residuals increases with increasing interevent distance for both subareas. According to the residual distribution, we can consider a value for interevent distance of 2–4 km for the cross-correlated data. At the final step of relocation, we exploit the ability of hypoDD to combine differential times derived from phase-picked data and waveform cross-correlation. We performed a joint inversion of all available differential times in order to obtain a highly accurate earthquake catalogue. A crucial part of the relocation process is the weighting and reweighting of the different kind of data (Waldhauser & Ellsworth 2000). For the current data sets, we used four sets with five iterations in each one and appropriate reweighting of the differential times. For the first 10 iterations, we downweight, by a factor of 100, the cross-correlation to allow location using only the catalogue data in larger interevent distances (5–6 km). Then, for the last 10 iterations we downweight, by a factor of 100, the pick data and let the cross-correlation differential times locate the earthquakes having shorter interevent distances (∼2 km). All the calculations were performed using the conjugate gradients method after appropriate damping of the data (LSQR, Paige & Saunders 1982). The final catalogue contains 22 078 events in the western part, almost 90 per cent of the initial events, and 4323 events in the eastern part, almost 88 per cent of the initial catalogue. Events are rejected during the relocation process due to insufficient number of phases and number of links after the application of the weighting function. In the western part, 64 per cent of the earthquakes were located using both cross-correlation and phase-picked data, whereas a remaining 36 per cent using only catalogue data, which mostly concerns earthquakes that occurred in the early period (before 2011) when the available stations were fewer. On the other hand, only 37 per cent of the earthquakes in the eastern part were relocated using both cross-correlation and phase-picked data and 63 per cent of them using only phase-picked data. The low percentage of cross-correlated events is most probably due to the large interevent distances, which results to few cross-correlation pairs. Fig. 4 presents the effect of interevent distance and magnitude difference to the CC. In the western part, the CC decreases with increasing interevent distance (Fig. 4a). A similar pattern is observed in the eastern part (Fig. 4b), where higher CCs were found, and could be considered as the result of cross-correlations concerning seismic excitations very restricted spatially (e.g. Villia sequence, 2013). The CC decreases with increasing difference in magnitude between event pairs in both subareas (Figs 4c and d). In the western part, the CC has a median lower than 90 per cent for ΔM ≤ 1.5, whereas in the eastern part the median approaches 90 per cent for ΔM ≤ 1.5. Figure 4. View largeDownload slide (a) and (b) Mean correlation coefficient against hypocentre separation in 100 m bins and (c) and (d) boxplots of correlation coefficient against difference in magnitude in bins of 0.5. Figure 4. View largeDownload slide (a) and (b) Mean correlation coefficient against hypocentre separation in 100 m bins and (c) and (d) boxplots of correlation coefficient against difference in magnitude in bins of 0.5. Fig. 5 shows the focal distribution obtained for each stage of the relocation process, along a vertical profile in an approximately N–S (195°) direction, almost normal to the dominant fault strike in both subareas. The initial locations derived from the routine analysis of different Institutes (GD-AUTh and NOA) exhibit an undefined cloud of seismicity, placed in depths between 0 and 20 km for both subareas (Figs 5a and b), mainly concentrated between 7 and 13 km for the western part. There are many alignments of the foci along horizontal lines at different depths, which more likely correspond to fixed depths or low resolution of the reported depths. After considering a local velocity model, a Vp/Vs ratio derived from the data and station corrections, the focal distribution is changed (Figs 5c and d). The foci of the western part are confined in a seismogenic zone 5 km thick (6–11 km depths, Fig. 5c) after the inclusion of stations corrections. In the eastern part, a change in focal depths distribution is also observed (Fig. 5d). The foci alignment is not observed in this stage. The relocation results after the application of hypoDD with the phase-picked data are shown in Figs 5(e) and (f). The seismogenic zone in the western region seems to be narrower without any significant shift in the cluster centroid (Fig. 5e). The final locations are shown in Figs 5(g) and (h), where the improvement in the locations is clearly shown. The seismogenic zone in the western part is still confined in the depth range 6–11 km (Fig. 5g). In the eastern part, the interevent distances are reduced but the seismicity is not concentrated at certain depths, instead it is evenly distributed between 3 and 13 km. Figure 5. View largeDownload slide Different stages of relocation process for the two areas of Corinth Gulf. (a) and (b) Initial location obtained from routine analysis, (c) and (d) application of single-event location with station corrections, (e) and (f) application of hypoDD with phase-picked data and (g) and (h) final locations after joint inversion of cross-correlation measurements and phase-picked data. Figure 5. View largeDownload slide Different stages of relocation process for the two areas of Corinth Gulf. (a) and (b) Initial location obtained from routine analysis, (c) and (d) application of single-event location with station corrections, (e) and (f) application of hypoDD with phase-picked data and (g) and (h) final locations after joint inversion of cross-correlation measurements and phase-picked data. 2.3 Error estimation Errors in the final locations estimated by hypoDD, using the LSQR method, are not representative of the real location errors (Waldhauser 2001). Their values are of the order of few metres (3–5 m) and have no physical meaning. In order to estimate the accuracy of the final locations, we perform error analysis concerning the time delay uncertainties and the effect of the station distribution to the final locations. First, a bootstrap resampling method (Efron 1982) is applied by creating 200 samples, with replacement, of the final residual vector derived from the double difference joint inversion. The residuals are then added to all differential traveltimes with unit weights and the relocation is repeated for each sample. The distribution of the differences between the final locations and the 200 samples is used to compute the 95 per cent confidence error ellipse per event. Table 1 summarizes the uncertainty estimates for each direction, type of data and subarea. It is observed that median errors are larger in the eastern part, whereas in the western part they are of the order of few hundred metres. In addition, it is shown that for both areas the phase-picked data have larger uncertainties than events located using both cross-correlation and phase-picked data. Table 1. Median errors of the relocated catalogue in the three directions for the different parts of Corinth Gulf and the different type of data (phase-pick and cross-correlation). All errors are in metres.   Western part  Eastern part  Direction  All  Phase pick  CC  All  Phase pick  CC  X  380  660  282  856  1230  617  Y  260  439  190  629  864  441  Z  300  513  221  655  933  436    Western part  Eastern part  Direction  All  Phase pick  CC  All  Phase pick  CC  X  380  660  282  856  1230  617  Y  260  439  190  629  864  441  Z  300  513  221  655  933  436  View Large Taking into account that the most recent earthquakes are located using cross-correlation differential times, we looked for any significant temporal variations in the errors. Fig. 6 shows the median errors in the three directions as a function of time for the two types of data (phase-picked and cross-correlation) in each subarea separately. The median errors are calculated within a moving window of 300 events and step of five events. For the western part (Fig. 6, upper panel), the errors for the cross-correlated data are decreasing with time. On the other hand, the phase-picked data have larger errors for the entire period with an increasing trend in the late years. This is due to the lower accuracy of the few remaining events relocated with phase data compared to cross-correlated ones. For the eastern part of the gulf (Fig. 6, lower panel), we do not observe a decreasing trend of error uncertainties with time. However, in two cases, which are associated with certain seismic excitations occurred in 2011 and 2013, respectively, a decrease in error is illustrated. This is mainly due to the high density of seismic activity in both excitations. The spatial distribution of the errors in three directions evidences that errors are smaller in areas where seismic activity is denser (Fig. C1). Figure 6. View largeDownload slide Median error in the three directions as a function of time for the phase-picked data (red lines) and the cross-correlated one (black lines) for the western (upper panel) and eastern Corinth Gulf (lower panel), respectively. Figure 6. View largeDownload slide Median error in the three directions as a function of time for the phase-picked data (red lines) and the cross-correlated one (black lines) for the western (upper panel) and eastern Corinth Gulf (lower panel), respectively. The effect of station distribution in the final locations is tested by applying a jackknife method (Efron 1982). Particularly, we repeat the relocation process of the initial data set by omitting one station at a time (Waldhauser & Ellsworth 2000). Then, we calculate the standard deviation of the differences between the initial locations and the ones obtained from the jackknife method for each event in the three spatial directions. The median errors for the western part are 101, 68 and 79 m for the two horizontal and the vertical directions, respectively. These values are significantly smaller than the ones introduced by noise in the data in bootstrapping method. The median errors in the eastern part are 123, 132 and 446 m for the three directions, respectively, implying that the network geometry affects the final locations. 3 MOMENT TENSORS Focal mechanisms are computed on a routine basis, for events with ML ≥ 4.0 occurring in the broader area of Greece, using regional or local data and different algorithms for waveform inversion (Konstantinou et al.2010; Roumelioti et al.2011; Serpetsidaki et al.2016). For the area of Corinth Gulf, several studies with fault plane solutions were performed, using P-wave onsets from a local network (e.g. Rigo et al.1996; Hatzfeld et al.2000; Godano et al.2014) or after studying a certain seismic excitation (e.g. Hatzfeld et al.1996; Karakostas et al.2012; Kapetanidis et al.2015; Mesimeri et al.2016). Waveform inversion techniques were also applied in the study area in order to compute fault plane solutions for moderate to strong events in several cases (e.g. Baker et al.1997; Evangelidis et al.2008; Zahradnik et al.2008; Sokos et al.2012). Aiming to obtain a reliable and homogeneous data set of fault plane solutions for the study area, we used the ISOLA software (Sokos & Zahradnik 2008, 2013) to compute centroid moment tensors for ML ≥ 3.0 events that occurred between 2011 and 2014. ISOLA uses the iterative deconvolution method of Kikuchi & Kanamori (1991) modified for regional distances. The set of stations used for relocation purposes is considered here along with the velocity model proposed by Rigo et al. (1996). The inversion was performed for a deviatoric moment tensor and the waveforms are filtered to a frequency range of 0.03–0.09 Hz. From the 58 events of the relocated catalogue with ML ≥ 3.5, we computed 50 moment tensors (86 per cent). Due to the density of the network, we were able to look for possible moment tensors for events within the magnitude range 3.0 ≤ ML < 3.5. Even though it is difficult to determine fault plane solutions for smaller magnitude earthquakes, we computed 22 focal mechanisms out of 116 events with 3.0 ≤ ML < 3.5 (∼18 per cent). The spatial distribution of the 72 focal mechanisms is shown in Fig. 7 and relevant information is provided in Appendix  A. Figure 7. View largeDownload slide Fault plane solutions obtained in this study. The boxes define the different subregions used for the estimation of the TSMT. Inset panel: TSMT solutions for the different subregions. Figure 7. View largeDownload slide Fault plane solutions obtained in this study. The boxes define the different subregions used for the estimation of the TSMT. Inset panel: TSMT solutions for the different subregions. At the latest version of ISOLA package, the user has the ability to estimate the quality and the uncertainties of the computed moment tensors using several quantitative criteria (Sokos & Zahradnik 2013). The first two estimated factors after the waveform inversion are the variance reduction (VR), which reflects the similarity between the synthetic and the observed waveforms, and the condition number (CN), which measures the stability of the inversion. Two additional indicators of solution quality regarding the space–time variability of the solution could be obtained. Focal-Mechanism Variability Index (FMVAR), which compares the obtained solutions with the optimal solution using the Kagan angle (Kagan 1991), and Space-Time Variability Index (STVAR), which measures the size of the space–time area corresponding to the given correlation threshold. The solutions with low values of FMVAR (<30) and STVAR (<0.30) are considered more stable. The aforementioned quantitative criteria are estimated for the 72 moment tensors computed in this study, which have CN < 7 with a mean value of 2.74 and mean VR equal to 0.5. The mean values of the FMVAR and STVAR parameters are 9.0 and 0.19, respectively, supporting solutions stability. For the 82 per cent of the solutions six or more stations are taken, a number which is considered quite satisfactory for the waveform inversion. The mean percentage participation of the double-couple component in the moment tensor is 85 per cent for the 72 moment tensors. In order to quantify the stress regime in the study area, we calculated the total seismic moment tensor (TSMT), which is the sum of the moment tensors calculated from the individual solutions   \begin{equation} M_{ij}^{{\rm{total}}} = \sum\limits_{k = 1}^N {M_0^km_{ij}^k} \end{equation} (1)where k is the number of earthquakes, M0 the scalar seismic moment of each event and mij the seismic moment tensor components (Buforn et al.2004). TSMT, compared to other approaches (e.g. Frohlich & Apperson 1992), has the advantage of taking into consideration the magnitude of each earthquake and using it as a weighting factor. As a result, the earthquakes with high M0 values have the largest contribution in the estimation of TSMT. The study area is now divided into eight subregions based on the spatial extent of the major faults in the area and the spatial distribution of the focal mechanisms (Fig. 7). For each subregion, we estimate the TSMT using only the focal mechanisms computed in this study (Fig. 7 inset panel and Table 2). Starting with the westernmost part north of the Patraikos Gulf (subregion 01), where the dominant structure is a left-lateral strike-slip fault (Evangelidis et al.2008; Kiratzi et al.2008; Kassaras et al.2014), we observe a right-lateral strike-slip motion near the Lake Trichonida, which is orthogonal to the left-lateral structure. Normal faults are prevalent in Corinth Gulf striking from 260° and gradually reaching 290° at the eastern edge. The mean strike in subregion 02 is 260°, where the Psathopyrgos fault is located, equal to 277° in subregion 03 (Aigion fault). In subregions 05, 06 and 07 the mean strikes are equal to 298°, 298° and 273°, respectively, showing a change in faulting orientation from north to south. The major faults in the area (Offshore Akrata, Xylokastro and Offshore Perachora) have a strike of 280°–290°, similar with that obtained from TSMT analysis in the southern part of the area. In 2013 May, an earthquake swarm took place in subregion 04 with more than 1500 earthquakes occurring in only months, revealing microstructures striking almost E-W. The focal mechanisms obtained here, using the ISOLA package and the waveform inversion method, are in accordance with those computed using P-wave onsets (Kapetanidis et al.2015; Mesimeri et al.2016) for events with smaller magnitudes (ML > 2.0). At the easternmost part (subregion 08), the TSMT reveals normal faulting striking SW–NE (240°). Table 2. Total Seismic Moment Tensor solutions (TSMT) for each subregion along with the number of fault plane solutions (FPS) used and the CLVD percentage.       Plane 1  Plane 2  T-axis  P-axis  Subregion  Number of FPS  CLVD (per cent)  Strike (°)  Dip (°)  Rake (°)  Strike (°)  Dip (°)  Rake (°)  Trend (°)  Coplunge (°)  Trend (°)  Coplunge (°)  01  3  16  63  66  174  155  85  25  21  69  286  77  02  23  15  263  43  −84  76  48  −95  169  87  292  5  03  24  3  277  27  −86  93  63  −92  185  72  359  18  04  5  1.5  271  36  −86  87  54  −92  179  81  347  9  05  5  2  289  71  −49  40  44  −152  351  74  242  43  06  6  1  298  22  −70  96  70  −98  193  66  354  25  07  4  5  273  31  −95  98  59  −87  186  76  16  14  08  2  2  240  42  −87  56  48  −93  148  87  297  4        Plane 1  Plane 2  T-axis  P-axis  Subregion  Number of FPS  CLVD (per cent)  Strike (°)  Dip (°)  Rake (°)  Strike (°)  Dip (°)  Rake (°)  Trend (°)  Coplunge (°)  Trend (°)  Coplunge (°)  01  3  16  63  66  174  155  85  25  21  69  286  77  02  23  15  263  43  −84  76  48  −95  169  87  292  5  03  24  3  277  27  −86  93  63  −92  185  72  359  18  04  5  1.5  271  36  −86  87  54  −92  179  81  347  9  05  5  2  289  71  −49  40  44  −152  351  74  242  43  06  6  1  298  22  −70  96  70  −98  193  66  354  25  07  4  5  273  31  −95  98  59  −87  186  76  16  14  08  2  2  240  42  −87  56  48  −93  148  87  297  4  View Large 4 DETERMINATION OF ACTIVE SEGMENTS AND SEISMOTECTONIC PROPERTIES In an attempt to identify the active fault segments in the study area by exploiting the high accuracy of the relocated seismicity, we looked for seismic excitations that took place in the Corinth Gulf during the time span of the relocated catalogue. The identification of seismic excitations, known as earthquake clusters, is performed using the CURATE algorithm (Jacobs et al.2013) on the relocated earthquake catalogue. CURATE focuses on periods when the seismicity rate is increased above the background rate in a given area, and identifies earthquake clusters by applying an interevent distance and day rule for each earthquake in the catalogue. Taking into consideration, the errors in hypocentre locations, calculated using the bootstrap method, we set a distance rule for the CURATE algorithm equal to 2 km for the western subarea. We chose a low value due to the high location accuracy and spatial density of the earthquakes, which are mainly associated with small fault segments. For the eastern part, the distance rule was set to 4 km due to the larger location errors. The day rule was set to two days for both subareas. The identified spatiotemporal clusters are initially filtered based on the number of events (N ≥ 10). Then, it was attempted to relate them to fault segments by constructing several cross-sections normal to a wide range of strikes for each identified cluster. The cross-section in which the foci delineate a seismogenic zone is selected as the most appropriate one in each case and the dip for each selected cross-section was measured. The search for earthquake clusters is performed for each subarea separately and a correlation between their spatial distribution and seismicity in the area is attempted. 4.1 Western Corinth Gulf In the western Corinth Gulf 185 clusters with 10 or more earthquakes are identified by CURATE algorithm, with 47 of them being related to fault segments dipping north (37) and south (10) with angles ranging from 30° to 65° and striking in the range 220°–300° and 90°–110°, respectively. The differences between the strikes and dips of the identified segments, and the TSMT solutions are shown in Table B1. The deviations indicate that seismic excitations take place not in patches of the major faults which are locked but in patches of buried/blind secondary faults in the area. In Fig. 8, the identified clusters with N ≥ 10 which occurred since 2011 are plotted (green circles) along with the clusters that are associated with a fault segment (red circles) and the background activity (white circles). The majority of the clusters are located offshore with only few onshore exceptions. It is notable that several clusters are located north of the fault associated with the 1995 Aigion Mw 6.5 earthquake (Bernard et al.1997), whereas a lack of earthquake clusters is observed north of the westernmost edge of Psathopyrgos fault. Forty two (42) of the 47 identified segments are associated with seismic excitations that occurred after 2011, indicating that the earlier locations or the network detectability were not adequate for defining fault segments. Figure 8. View largeDownload slide Spatial distribution of the relocated catalogue occurred since 2011 in the western Corinth Gulf along with the major faults in the area (see Fig. 1). White circles show seismicity that is not part of a cluster, green circles show events that are members of a cluster with N ≥ 10, whereas red circles show the clusters that are associated with a fault segment. The epicentres of the Aigio 2013 earthquake swarm obtained from Mesimeri et al. (2016) are depicted with magenta. The traces of the fault segments at the mean depth of each cluster are shown with thick black lines and thin black lines correspond to the vertical cross-sections shown in Fig. 9. Figure 8. View largeDownload slide Spatial distribution of the relocated catalogue occurred since 2011 in the western Corinth Gulf along with the major faults in the area (see Fig. 1). White circles show seismicity that is not part of a cluster, green circles show events that are members of a cluster with N ≥ 10, whereas red circles show the clusters that are associated with a fault segment. The epicentres of the Aigio 2013 earthquake swarm obtained from Mesimeri et al. (2016) are depicted with magenta. The traces of the fault segments at the mean depth of each cluster are shown with thick black lines and thin black lines correspond to the vertical cross-sections shown in Fig. 9. We constructed a set of 20 cross-sections (Fig. 9) normal to the main strike of the rift, taking into account the major north-dipping faults, the fault plane solutions and the TSMTs computed in this study, in order to correlate the earthquake clusters with the spatial distribution of seismicity. Considering the time dependency of the errors, we plot the events which occurred between 2008 and 2010 in the background (grey circles) in order to compare them with the ones that occurred later (2011–2014, black circles). Earthquakes belonging to clusters were plotted as in the map of Fig. 9. Figure 9. View large Download slide View large Download slide Set of 20, normal to the main trend of the gulf, cross-sections as denoted in Fig. 8. Black dots show the earthquakes that occurred since 2011, whereas grey dots show the seismicity from 2008 to 2010. Green dots show the clusters with N ≥ 10, red dots show the clusters related to a fault segment and magenta dots show the Aigio 2013 earthquake swarm (Mesimeri et al.2016). Black lines indicate the major faults. The width of each cross-sections is 3 km. Figure 9. View large Download slide View large Download slide Set of 20, normal to the main trend of the gulf, cross-sections as denoted in Fig. 8. Black dots show the earthquakes that occurred since 2011, whereas grey dots show the seismicity from 2008 to 2010. Green dots show the clusters with N ≥ 10, red dots show the clusters related to a fault segment and magenta dots show the Aigio 2013 earthquake swarm (Mesimeri et al.2016). Black lines indicate the major faults. The width of each cross-sections is 3 km. The earthquakes of the first two cross-sections (W01 and W02) are located in the Patraikos Gulf, where the seismicity is sparse and the dominant strike differs from the rest of the study area. The foci distribution is comprised into almost vertical groups of seismicity, which have been identified as spatiotemporal clusters but are not associated with a fault segment, and clusters (red circles) defining segments striking at 250°–260°. The W03–W20 cross-sections are normal to a mean strike of 285°N, even though the segments defined by the earthquake clusters have variable strikes. In cross-sections W03–W05, earthquake clusters and background activity occur at focal depths of 7–12 km. A different pattern is illustrated in the next four cross-sections (W06–W09), where the most recent events (black circles) form a very narrow, shallow north-dipping zone, which initially has a shorter length but becomes longer as we move to the east. The earthquake clusters that are associated with fault segments (red circles) or they do not define any structure (green circles) occur at shallower depths. Few events belonging to spatiotemporal clusters that are found very close to the narrow zone are located with larger errors (>300 m), whereas their cluster centroid is shallower. It is also noteworthy that the earthquakes in this cross-section are located in the area between the two major faults Aigion and Psathopyrgos (Fig. 8). Comparison between the two data sets, namely, the 2008–2010 (grey dots in Fig. 9) and 2011–2014 (black dots in Fig. 9), shows that the earlier ones form a cloud around the later ones, revealing the location improvement with time. Moving further to the east (W10–W14) across the Aigion fault, we observe that the defined clusters and the background activity are located at the same depths. A different pattern is observed during the 2013 Aigion swarm (magenta circles), illustrated in cross-sections W12–W14 (Fig. 9). This cross-section contains the well-studied earthquake swarm, which was initiated in 2013 May and lasted almost three months (Chouliaras et al.2015; Kapetanidis et al.2015; Mesimeri et al.2016; Kaviris et al.2017). It reveals a north-dipping structure at the southern part of the western Corinth Gulf. This activity is located south of the shallow north-dipping seismic zone and could not be associated with the offshore activity. Finally, east of W14 cross-section, the last six cross-sections (W15–W20) were constructed in an area with sparse seismicity where the association of clusters with active fault segments is not feasible. As we reach the eastern part of Corinth Gulf, the seismicity is reduced and this pattern continues to the eastern Corinth Gulf. 4.2 Eastern Corinth Gulf After applying the CURATE algorithm 35, spatiotemporal clusters with at least 10 events are identified and two of them are related to a certain fault segment. The first cluster that is related to a fault segment occurred in 2009 May following an ML = 4.4 earthquake. The second one refers to the Villia sequence that occurred in 2013 June near Kaparelli fault and lasted approximately one month (Kaviris et al.2014, Appendix  B). In Fig. 10, we show the spatial distribution of the background activity (white circles) along with the identified spatiotemporal clusters with N ≥ 10 (green circles) and those that are related to fault segments (red circles). As in the western part, we consider only events since 2011 due to the improvement in the location accuracy. Figure 10. View largeDownload slide Spatial distribution of the relocated catalogue for the eastern Corinth Gulf along with the major faults in the area. The notation is the same as in Fig. 8. Figure 10. View largeDownload slide Spatial distribution of the relocated catalogue for the eastern Corinth Gulf along with the major faults in the area. The notation is the same as in Fig. 8. A set of 18 cross-sections (Fig. 10) are constructed normal to the main orientation of the eastern part keeping the same notation as in Fig. 9. A clear difference in the seismicity distribution is observed, compared to the western part. In the first 15 cross-sections (Fig. 11), we could not define any structure, but a pattern of vertical distributions of foci, which in several cases are identified as spatiotemporal clusters (green circles), is depicted. An example of this pattern is the E06 cross-section, which shows two vertical groups of foci in different depths (green circles). Most of these events occurred in 2012 September following an Mw = 5.1 earthquake. Due to the vertical distribution of the foci, we looked for a possible relation to fluid intrusion by applying distance–time plots. These plots, in cases of fluid intrusion, describe the migration of seismicity, which is evident by a characteristic triggering front (Shapiro 2015). However, for this particular sequence, we did not find evidence for fluid migration, whereas a further examination of fluid intrusion in the eastern Corinth Gulf is beyond the scope of this study. Figure 11. View largeDownload slide Set of 18, normal to the main trend of the gulf, cross-sections as denoted in Fig. 10. The notation is the same as in Fig. 9. Figure 11. View largeDownload slide Set of 18, normal to the main trend of the gulf, cross-sections as denoted in Fig. 10. The notation is the same as in Fig. 9. At the easternmost part of the study area, the dominant fault strike is again changing, also shown by the TSMTs. The final three cross-sections (E16–E18) include the 2013 Villia sequence (E17 red circles) and two sequences that occurred in 2009 (E18 grey circles) and 2013 (E16 green circles), respectively. A south-dipping structure related to the Villia sequence (2013 June) is shown in cross-section E17, located at focal depths of 7–9 km. The 2009 sequence located south of the Villia sequence forms an almost vertical structure confined in shallower depths, very close to the surface. Due to the sparse seismicity in the area, with only two exceptions, the location accuracy is not adequate for making strong conclusions about the active structures in the area. 5 DISCUSSION A highly accurate earthquake catalogue for the area of Corinth Gulf is compiled for the first time, using the data of the HUSN from 2008 to 2014. Approximately 22 000 events are located in the western study area, which is twice the number of events in the relocated catalogue of Lambotte et al. (2014) which however covers a different time period (2000–2007). Additionally, for the first time a massive relocation of recent seismicity has been performed for the eastern Corinth Gulf (∼4000 events). The catalogue is considered highly accurate, especially in the western Corinth Gulf, with the uncertainty in horizontal and vertical directions of the order of few hundred metres. The major finding of this study is that the spatial distribution of the relocated seismicity revealed two patterns of activity in the western subarea, namely, strongly clustered seismicity in both space and time in depths shallower than 10 km and below that activity a very narrow shallow north-dipping zone void of spatiotemporal clusters. The earthquake clusters identified in the western subarea, after applying certain space–time criteria, were examined and related to 47 fault segments having variable strikes and dipping either to the north or to the south. The majority of the clusters are located offshore between 22.00° and 22.20°Ε with high dip angles [40°–60°], strikes of 270°–290° and their depths in the range 6–10 km. In the westernmost part of the study area, few clusters are aligned at slightly different strikes [250°–270°]. The north-dipping seismic zone observed in several previous seismicity studies (Rietbrock et al.1996; Rigo et al.1996; Hatzfeld et al.2000; Lyon-Caen et al.2004; Bernard et al.2006; Lambotte et al.2014) is also identified in this study, particularly in the W06–W09 (Figs 8 and 9) cross-sections. However, the underlying mechanism that triggers the seismicity in this seismic zone has been questioned for over three decades. We found here that the observed shallow north-dipping seismic zone is free of spatiotemporal earthquake clusters and the activity is continuous throughout the study period. The space–time-clustered events (earthquake clusters) are located in different parts of the rift, whereas only a few of them are located above the shallow north-dipping seismic zone in shallower depths. Assuming that the multiplets defined by Lambotte et al. (2014) are comprised in the same shallow north-dipping seismic zone that is found in this study, we observe that these multiplets last several years, and in a few cases, span the entire period of the CRL operation (table A1 in Lambotte et al.2014). Additionally, there is no seismic activity below the shallow north-dipping seismic zone, as it is illustrated in the cross-sections (Fig. 9). Thus, the continuous microseismic activity, observed only in the western part of Corinth Gulf, most probably defines the seismic–aseismic transition (Hatzfeld et al.2000). The seismicity in the eastern subarea is relatively low and highly sparse compared to the western Corinth Gulf. Two out of the 35 spatiotemporal clusters identified in the study period are related to a certain fault segment. The most recent cluster related to a fault segment occurred in 2013 June, lasted almost one month and comprised some hundreds events with magnitudes 0.5 ≤ ML ≤ 3.5 (cluster E01, Table B1). This activity forms a south-dipping structure (E17 in Fig. 11) and exhibits similar characteristics as the Kaparelli fault, which was activated during the 1981 Alkyonides sequence (Papazachos et al.1984; King et al.1985). In a few cases (E06 and E18 in Fig. 11), it appeared that seismic activity is clustered in shallow depths and forms almost vertical lines, which could not be attributed to any known fault segment. However, the location uncertainty, the limited data, as well as the local network geometry are not favourable for making strong conclusions. The moment tensors computed for 72 earthquakes using waveform inversion techniques and the fault plane solutions are in accordance with the N–S extension of the rift. We followed a different approach from Godano et al. (2014) as we considered events with M ≥ 3.0 for the entire Corinth Gulf regardless of their correlation with earthquake clusters. However, the results of both studies are quite similar for the central part of the western subarea. The computation of total moment seismic tensor for eight different subregions revealed gradual strike changes from west to east. The seismic activity is still on near Trichonida Lake with few strike-slip fault plane solutions, which exhibit SW–NE orientation, perpendicular to the spatial alignment of the 1975 aftershock sequence and the 2007 swarm (Kiratzi et al.2008; Kassaras et al.2014). The faults of the westernmost and the easternmost extremities are striking almost at 250°. 6 CONCLUSIONS A firm conclusion traced in this study is that the difference in seismicity between the two parts of the Corinth Gulf is clearly depicted and can be attributed to the different extension rates estimated from geodetic data. The highly accurate catalogue defines in great detail the existence of a shallow north-dipping seismic zone which lacks of spatiotemporal earthquake clusters and is characterized by continuous seismic activity. It is evident that the seismic activity ceases below this structure and the lower depth can be interpreted as the boundary between the seismic and aseismic layers. The absence of recent strong earthquakes (M > 6.0) in the dominant faults (Psathopyrgos and Aigion) along with spatially clustered continuing activity raises questions about the possibility of creeping faults in that area. Thus, the full exploitation of the recorded seismic activity, the catalogue compilation and its future updates will be a valuable tool in the direction of understanding the underlying mechanism of earthquake process in the Corinth Gulf and constitutes an indispensable component for any seismic hazard assessment study. ACKNOWLEDGEMENTS The authors appreciate the editorial assistance of Prof Egill Hauksson and the constructive comments of two anonymous reviewers, which contributed to the improvement of the manuscript. Some figures were plotted using GMT (Wessel & Smith 1998). Geophysics Department Contribution 905. REFERENCES Ambraseys N., 2009. Earthquakes in the Mediterranean and Middle East: A 725 Multidisciplinary Study of Seismicity up to 1900 , Cambridge Univ. Press, 947 pp. Google Scholar CrossRef Search ADS   Armijo R., Meyer B., King G.C.P., Rigo A., Papanastasiou D., 1996. Quaternary evolution of the Corinth Rift and its implications for the Late Cenozoic evolution of the Aegean, Geophys. J. Int. , 126, 11– 53. Google Scholar CrossRef Search ADS   Avallone A. et al., 2004. Analysis of eleven years of deformation measured by GPS in the Corinth Rift Laboratory area, C. R. Geosci. , 336, 301– 311. 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Google Scholar CrossRef Search ADS   APPENDIX A: FAULT PLANE SOLUTIONS Table A1. Fault plane solutions for 72 events with ML ≥ 3.0 occurred in the Corinth Gulf in 2011–2014.                   Plane 1  Plane 2  P-axis  T-axis            Year  Date  Origin time  Latitude (°N)  Longitude (°E)  Depth (km)  ML  Mw  M (N m)  Strike (°)  Dip (°)  Rake (°)  Strike (°)  Dip (°)  Rake (°)  Trend (°)  Plunge (°)  Trend (°)  Plunge (°)  VR  CN  N  FMVAR  STVAR  2011  02 05  02:52:38.47  38.4179  22.0244  7.79  3.5  3.6  3.662 × 1014  307  70  −79  97  22  −118  234  63  28  25  0.18  3.4  7  8  0.12  2011  02 11  17:56:56.00  38.3932  21.7899  10.12  4.2  4.0  1.407 × 1015  129  90  −25  219  65  −180  81  17  176  17  0.70  2.1  10  9  0.24  2011  02 12  11:37:36.58  38.3897  21.7895  10.99  3.6  3.7  3.999 × 1014  224  71  168  319  78  20  91  5  183  22  0.32  1.9  9  10  0.23  2011  02 20  19:24:07.94  38.4991  21.6624  14.46  3.3  3.6  2.842 × 1014  75  72  −179  344  89  −18  298  14  31  12  0.50  2.3  8  8  0.24  2011  02 20  21:57:16.62  38.5002  21.6627  14.36  3.7  3.7  3.958 × 1014  341  85  −31  74  59  −174  293  25  31  18  0.54  2.3  9  9  0.23  2011  02 24  23:29:46.08  38.3904  21.8013  10.71  3.7  3.6  3.390 × 1014  126  59  −22  228  71  −147  91  36  355  7  0.27  3.0  7  21  0.33  2011  04 13  02:32:27.09  38.2667  22.1924  9.68  3.4  3.4  1.394 × 1014  269  19  84  83  71  −92  349  64  174  26  0.27  2.6  5  7  0.09  2011  05 04  12:39:42.86  38.2867  22.3976  13.27  4.0  3.8  6.153 × 1014  89  60  −88  264  31  −94  5  75  177  15  0.62  1.9  7  7  0.20  2011  05 04  14:35:15.76  38.3457  21.8141  9.90  3.6  3.4  1.881 × 1014  242  23  −140  114  75  −72  48  56  190  28  0.42  4.0  7  9  0.11  2011  06 06  11:06:01.57  38.4366  21.8307  13.09  3.4  3.4  1.672 × 1014  257  26  −106  94  65  −83  19  69  178  20  0.54  2.6  5  6  0.24  2011  06 07  23:39:15.06  38.4318  22.0633  6.55  3.3  3.2  7.355 × 1013  256  28  −83  68  63  −94  330  72  161  18  0.62  5.4  5  9  0.03  2011  07 18  03:58:51.62  38.2368  22.5373  19.19  3.3  3.3  9.813 × 1013  305  34  −54  83  63  −111  316  65  189  16  0.43  1.9  6  13  0.21  2012  07 16  20:26:48.44  38.3947  22.0013  9.64  3.1  3.3  1.161 × 1014  291  28  −79  99  63  −96  356  72  193  18  0.57  2.1  6  5  0.26  2012  08 16  21:22:54.36  38.2661  22.5302  14.40  3.5  3.7  4.153 × 1014  234  57  −131  111  50  −45  87  57  351  4  0.36  1.7  9  7  0.26  2012  09 08  16:40:14.70  38.3757  22.0631  10.59  3.7  3.5  2.456 × 1014  322  30  −56  104  66  −108  343  65  207  19  0.28  1.8  8  8  0.30  2012  09 19  00:55:36.94  38.351  22.3146  15.51  3.1  3.3  1.239 × 1014  299  31  −64  89  63  −105  330  69  190  17  0.53  1.9  4  9  0.28  2012  09 21  15:21:21.12  38.3534  22.0147  8.41  3.9  3.9  8.287 × 1014  292  23  −75  95  67  −96  354  67  190  22  0.59  1.9  10  7  0.20  2012  09 22  03:52:24.52  38.0740  22.7446  15.99  5.1  4.9  2.660 × 1016  300  21  −68  96  71  −98  353  63  193  25  0.60  1.7  12  8  0.29  2012  10 18  19:27:53.28  38.5509  21.9171  18.69  3.1  3.3  1.319 × 1014  238  48  −131  110  56  −54  77  61  175  4  0.44  1.9  5  4  0.22  2012  12 09  01:23:06.11  37.9479  22.6038  10.28  4.1  4.0  1.313 × 1015  271  30  −97  99  60  −86  19  75  186  15  0.46  1.8  9  5  0.21  2012  12 27  23:20:53.86  38.2181  21.8490  9.06  3.8  3.9  9.652 × 1014  255  35  −138  128  68  −63  76  58  198  18  0.80  2.0  10  13  0.26  2013  01 28  04:14:06.67  38.3250  22.1627  9.52  3.6  3.7  4.707 × 1014  277  27  −83  89  63  −94  351  72  182  18  0.54  2.1  12  11  0.21  2013  05 19  12:00:41.08  38.3916  21.7607  13.88  3.1  3.3  1.013 × 1014  203  46  −135  78  60  −54  40  58  143  8  0.27  2.4  8  11  0.23  2013  05 28  01:13:00.49  38.2261  22.1059  9.85  3.6  3.6  3.109 × 1014  287  42  −67  78  52  −109  290  74  181  5  0.44  2.7  9  8  0.17  2013  05 31  08:57:25.28  38.2293  22.1097  10.14  4.0  3.7  3.856 × 1014  226  26  −112  71  66  −79  0  67  153  20  0.44  2.2  10  5  0.23  2013  06 11  19:36:16.60  38.1590  23.1956  10.00  3.5  3.6  3.128 × 1014  252  26  −73  54  65  −98  307  69  150  20  0.36  1.8  8  10  0.25  2013  06 27  17:24:43.40  38.2169  22.1197  9.18  3.8  3.8  5.454 × 1014  103  48  −91  285  42  −89  358  87  194  3  0.53  2.0  7  8  0.24  2013  07 09  21:46:19.96  38.4156  21.9633  9.80  3.1  3.2  8.332 × 1013  282  26  −75  85  65  −97  340  70  181  19  0.44  3.0  6  13  0.27  2013  07 14  07:46:58.39  38.2298  22.0917  10.95  3.3  3.5  2.006 × 1014  256  40  −105  95  51  −78  57  79  176  5  0.85  3.2  5  24  0.22  2013  07 24  02:55:49.81  38.2298  22.0986  10.98  3.5  3.7  4.312 × 1014  263  39  −98  94  51  −83  41  82  179  6  0.70  2.1  9  6  0.16  2013  09 20  02:05:19.26  38.1670  23.1052  13.42  4.4  4.4  4.304 × 1015  56  47  −92  238  43  −88  301  87  147  2  0.34  2.0  11  6  0.25  2013  09 26  02:34:36.34  38.3019  22.1353  8.39  3.7  3.8  7.233 × 1014  261  25  −103  95  65  −84  17  69  181  20  0.81  2.5  6  6  0.13  2013  09 26  05:25:12.02  38.2999  22.1292  8.85  3.1  3.1  6.028 × 1013  246  21  −121  99  73  −79  26  61  180  27  0.40  2.5  5  12  0.21  2013  10 22  03:38:57.90  38.3669  21.8797  8.19  3.1  3.1  9.891 × 1013  131  59  −13  227  79  −148  93  30  355  13  0.76  2.7  6  13  0.22  2013  12 09  08:59:35.62  38.3807  21.7454  14.54  3.7  3.6  3.308 × 1014  64  47  −74  221  45  −106  47  78  143  1  0.54  1.7  7  6  0.19  2013  12 22  18:04:02.94  37.8548  22.7335  13.74  3.5  3.6  3.080 × 1014  293  36  −82  103  54  −96  349  80  197  9  0.23  1.4  6  5  0.29  2014  01 24  22:08:48.30  38.3374  21.9980  7.91  3.8  3.8  6.244 × 1014  311  49  −65  96  47  −115  291  72  24  1  0.48  3.6  9  9  0.09  2014  01 29  09:14:23.47  38.3411  21.9822  8.48  3.9  4.1  1.637 × 1015  306  52  −72  98  41  −112  273  75  24  5  0.72  5.6  7  8  0.06  2014  01 29  18:23:44.88  38.342  21.9804  8.47  3.1  3.3  1.31 × 1014  310  60  −66  88  38  −125  264  66  23  12  0.53  6.3  6  15  0.11  2014  01 30  23:48:14.98  38.3857  21.8672  9.04  3.7  3.7  4.311 × 1014  231  26  −132  96  71  −72  31  60  172  24  0.57  2.9  7  11  0.22  2014  02 04  18:19:32.44  38.3397  21.9749  8.94  3.4  3.5  2.501 × 1014  311  58  −57  81  45  −131  275  62  18  7  0.63  6.8  6  9  0.06  2014  02 04  22:49:01.50  38.3339  21.9769  8.67  3.9  3.9  7.897 × 1014  111  45  −93  296  45  −87  282  88  23  0  0.73  5.1  7  9  0.04  2014  02 07  01:21:53.22  38.3144  21.7066  16.29  4.3  4.2  2.221 × 1015  303  77  −41  44  51  −163  255  37  359  17  0.65  2.1  9  12  0.28  2014  02 12  07:41:01.26  37.9327  22.5926  11.70  3.5  3.5  2.315 × 1014  264  29  −109  105  63  −80  36  70  188  18  0.13  2.1  5  6  0.22  2014  02 28  22:13:55.08  38.1975  22.5207  8.14  3.5  3.7  3.920 × 1014  300  33  −63  88  61  −107  323  69  190  14  0.24  2.1  8  9  0.15  2014  03 21  18:35:49.92  38.4122  22.4547  10.21  4.0  3.9  7.537 × 1014  25  41  −171  288  84  −49  234  37  347  27  0.51  2.0  10  11  0.27  2014  04 07  20:15:11.86  38.3348  21.8022  9.29  3.2  3.3  1.01 × 1014  232  25  −140  105  74  −70  41  57  179  26  0.74  3.5  4  11  0.14  2014  04 10  17:40:45.16  37.9305  22.5980  10.47  3.5  3.5  2.577 × 1014  110  48  −78  273  43  −103  84  81  192  3  0.12  1.7  5  8  0.25  2014  04 17  07:04:04.56  38.4092  22.4625  9.57  3.7  3.8  5.569 × 1014  281  64  −56  44  42  −138  237  57  347  12  0.20  1.9  10  20  0.28  2014  04 18  05:07:36.93  38.4223  21.8443  11.25  4.2  3.9  7.888 × 1014  102  86  −72  204  18  −168  30  46  176  39  0.63  3.0  7  13  0.33  2014  05 10  03:04:50.13  38.4164  22.4471  9.99  4.2  4.1  1.889 × 1015  286  69  −64  53  33  −138  232  58  357  19  0.31  2.2  9  11  0.35  2014  05 11  17:34:06.24  38.4361  21.6997  15.02  3.6  3.6  2.879 × 1014  38  78  173  130  83  12  264  3  354  13  0.73  2.7  8  8  0.27  2014  06 08  15:10:51.81  38.3260  22.0525  4.30  4.3  4.2  2.506 × 1015  105  46  −84  276  45  −97  95  85  191  0  0.53  2.1  12  4  0.09  2014  06 10  02:14:30.72  38.3332  22.062  8.76  3.3  3.5  1.96 × 1014  95  46  −91  277  44  −89  328  89  186  1  0.30  2.5  8  7  0.14  2014  06 10  22:52:42.08  38.3315  22.0668  8.15  3.6  3.5  2.196 × 1014  272  57  −100  110  34  −75  154  76  9  12  0.51  2.2  5  12  0.18  2014  06 20  01:53:28.78  38.323  22.0492  8.32  3.3  3.4  1.754 × 1014  112  41  −90  291  49  −90  200  86  22  4  0.39  4.3  8  5  0.07  2014  06 25  09:21:41.85  38.3597  21.7543  17.93  4.2  4.1  1.605 × 1015  197  69  −136  88  50  −28  60  45  318  12  0.40  2.1  9  14  0.29  2014  06 27  00:47:23.63  38.3852  21.9995  9.44  3.0  3.2  8.258 × 1013  325  31  −53  104  66  −110  341  64  209  19  0.49  2.6  7  9  0.35  2014  07 30  07:56:35.32  38.3487  21.8156  9.74  3.4  3.4  1.877 × 1014  239  24  −125  97  70  −76  29  62  176  24  0.40  2.5  10  9  0.16  2014  08 09  22:22:24.28  38.3603  21.8744  8.51  3.0  3.0  4.529 × 1013  236  39  −120  93  57  −67  53  69  167  9  0.56  2.9  4  15  0.17  2014  08 12  04:06:16.20  38.3992  22.5064  10.05  3.4  3.4  1.462 × 1014  255  30  −101  87  60  −84  14  74  173  15  0.56  1.9  6  5  0.24  2014  08 28  04:11:12.25  38.4129  22.4655  10.62  3.3  3.4  1.451 × 1014  302  65  −61  69  38  −136  254  59  11  15  0.70  3.1  6  21  0.10  2014  09 03  00:58:47.98  38.3379  21.9031  6.85  3.5  3.8  5.454 × 1014  78  18  −91  259  72  −90  169  63  348  27  0.36  4.7  5  9  0.08  2014  09 19  09:33:24.85  38.3620  21.8255  8.76  3.5  3.7  4.038 × 1014  274  53  −65  56  44  −119  243  69  346  5  0.41  3.1  11  6  0.12  2014  09 19  15:35:08.84  38.3687  21.8372  10.27  4.1  4.1  1.619 × 1015  86  54  −88  262  37  −93  7  81  174  9  0.60  2.8  8  4  0.11  2014  09 21  00:43:39.42  38.3477  21.8381  9.50  4.6  4.8  1.780 × 1016  70  47  −102  268  44  −77  269  81  169  2  0.74  4.9  10  3  0.04  2014  09 21  01:13:26.45  38.3637  21.8235  9.25  4.0  4.3  3.008 × 1015  271  42  −78  74  49  −101  283  81  172  3  0.70  2.9  11  5  0.08  2014  09 25  02:04:24.34  38.3511  21.8079  10.52  3.7  3.9  9.637 × 1014  269  55  −82  76  35  −101  206  78  354  10  0.39  4.6  12  7  0.03  2014  09 26  04:33:32.17  38.3447  21.9647  9.38  3.8  3.9  8.386 × 1014  293  51  −73  88  41  −110  260  76  11  5  0.56  2.4  9  7  0.03  2014  10 30  06:09:09.20  38.1461  22.6267  9.18  3.7  3.9  8.056 × 1014  293  42  −70  87  51  −107  298  76  189  5  0.19  2.6  7  2  0.09  2014  11 07  17:12:59.68  38.2890  22.1226  8.51  4.8  4.9  3.261 × 1016  270  23  −96  96  67  −88  10  67  184  22  0.75  3.0  13  3  0.07  2014  12 09  17:08:29.00  38.4047  22.2319  14.68  3.6  3.5  1.890 × 1014  122  23  −94  307  67  −88  220  68  36  22  0.48  2.0  8  5  0.30                    Plane 1  Plane 2  P-axis  T-axis            Year  Date  Origin time  Latitude (°N)  Longitude (°E)  Depth (km)  ML  Mw  M (N m)  Strike (°)  Dip (°)  Rake (°)  Strike (°)  Dip (°)  Rake (°)  Trend (°)  Plunge (°)  Trend (°)  Plunge (°)  VR  CN  N  FMVAR  STVAR  2011  02 05  02:52:38.47  38.4179  22.0244  7.79  3.5  3.6  3.662 × 1014  307  70  −79  97  22  −118  234  63  28  25  0.18  3.4  7  8  0.12  2011  02 11  17:56:56.00  38.3932  21.7899  10.12  4.2  4.0  1.407 × 1015  129  90  −25  219  65  −180  81  17  176  17  0.70  2.1  10  9  0.24  2011  02 12  11:37:36.58  38.3897  21.7895  10.99  3.6  3.7  3.999 × 1014  224  71  168  319  78  20  91  5  183  22  0.32  1.9  9  10  0.23  2011  02 20  19:24:07.94  38.4991  21.6624  14.46  3.3  3.6  2.842 × 1014  75  72  −179  344  89  −18  298  14  31  12  0.50  2.3  8  8  0.24  2011  02 20  21:57:16.62  38.5002  21.6627  14.36  3.7  3.7  3.958 × 1014  341  85  −31  74  59  −174  293  25  31  18  0.54  2.3  9  9  0.23  2011  02 24  23:29:46.08  38.3904  21.8013  10.71  3.7  3.6  3.390 × 1014  126  59  −22  228  71  −147  91  36  355  7  0.27  3.0  7  21  0.33  2011  04 13  02:32:27.09  38.2667  22.1924  9.68  3.4  3.4  1.394 × 1014  269  19  84  83  71  −92  349  64  174  26  0.27  2.6  5  7  0.09  2011  05 04  12:39:42.86  38.2867  22.3976  13.27  4.0  3.8  6.153 × 1014  89  60  −88  264  31  −94  5  75  177  15  0.62  1.9  7  7  0.20  2011  05 04  14:35:15.76  38.3457  21.8141  9.90  3.6  3.4  1.881 × 1014  242  23  −140  114  75  −72  48  56  190  28  0.42  4.0  7  9  0.11  2011  06 06  11:06:01.57  38.4366  21.8307  13.09  3.4  3.4  1.672 × 1014  257  26  −106  94  65  −83  19  69  178  20  0.54  2.6  5  6  0.24  2011  06 07  23:39:15.06  38.4318  22.0633  6.55  3.3  3.2  7.355 × 1013  256  28  −83  68  63  −94  330  72  161  18  0.62  5.4  5  9  0.03  2011  07 18  03:58:51.62  38.2368  22.5373  19.19  3.3  3.3  9.813 × 1013  305  34  −54  83  63  −111  316  65  189  16  0.43  1.9  6  13  0.21  2012  07 16  20:26:48.44  38.3947  22.0013  9.64  3.1  3.3  1.161 × 1014  291  28  −79  99  63  −96  356  72  193  18  0.57  2.1  6  5  0.26  2012  08 16  21:22:54.36  38.2661  22.5302  14.40  3.5  3.7  4.153 × 1014  234  57  −131  111  50  −45  87  57  351  4  0.36  1.7  9  7  0.26  2012  09 08  16:40:14.70  38.3757  22.0631  10.59  3.7  3.5  2.456 × 1014  322  30  −56  104  66  −108  343  65  207  19  0.28  1.8  8  8  0.30  2012  09 19  00:55:36.94  38.351  22.3146  15.51  3.1  3.3  1.239 × 1014  299  31  −64  89  63  −105  330  69  190  17  0.53  1.9  4  9  0.28  2012  09 21  15:21:21.12  38.3534  22.0147  8.41  3.9  3.9  8.287 × 1014  292  23  −75  95  67  −96  354  67  190  22  0.59  1.9  10  7  0.20  2012  09 22  03:52:24.52  38.0740  22.7446  15.99  5.1  4.9  2.660 × 1016  300  21  −68  96  71  −98  353  63  193  25  0.60  1.7  12  8  0.29  2012  10 18  19:27:53.28  38.5509  21.9171  18.69  3.1  3.3  1.319 × 1014  238  48  −131  110  56  −54  77  61  175  4  0.44  1.9  5  4  0.22  2012  12 09  01:23:06.11  37.9479  22.6038  10.28  4.1  4.0  1.313 × 1015  271  30  −97  99  60  −86  19  75  186  15  0.46  1.8  9  5  0.21  2012  12 27  23:20:53.86  38.2181  21.8490  9.06  3.8  3.9  9.652 × 1014  255  35  −138  128  68  −63  76  58  198  18  0.80  2.0  10  13  0.26  2013  01 28  04:14:06.67  38.3250  22.1627  9.52  3.6  3.7  4.707 × 1014  277  27  −83  89  63  −94  351  72  182  18  0.54  2.1  12  11  0.21  2013  05 19  12:00:41.08  38.3916  21.7607  13.88  3.1  3.3  1.013 × 1014  203  46  −135  78  60  −54  40  58  143  8  0.27  2.4  8  11  0.23  2013  05 28  01:13:00.49  38.2261  22.1059  9.85  3.6  3.6  3.109 × 1014  287  42  −67  78  52  −109  290  74  181  5  0.44  2.7  9  8  0.17  2013  05 31  08:57:25.28  38.2293  22.1097  10.14  4.0  3.7  3.856 × 1014  226  26  −112  71  66  −79  0  67  153  20  0.44  2.2  10  5  0.23  2013  06 11  19:36:16.60  38.1590  23.1956  10.00  3.5  3.6  3.128 × 1014  252  26  −73  54  65  −98  307  69  150  20  0.36  1.8  8  10  0.25  2013  06 27  17:24:43.40  38.2169  22.1197  9.18  3.8  3.8  5.454 × 1014  103  48  −91  285  42  −89  358  87  194  3  0.53  2.0  7  8  0.24  2013  07 09  21:46:19.96  38.4156  21.9633  9.80  3.1  3.2  8.332 × 1013  282  26  −75  85  65  −97  340  70  181  19  0.44  3.0  6  13  0.27  2013  07 14  07:46:58.39  38.2298  22.0917  10.95  3.3  3.5  2.006 × 1014  256  40  −105  95  51  −78  57  79  176  5  0.85  3.2  5  24  0.22  2013  07 24  02:55:49.81  38.2298  22.0986  10.98  3.5  3.7  4.312 × 1014  263  39  −98  94  51  −83  41  82  179  6  0.70  2.1  9  6  0.16  2013  09 20  02:05:19.26  38.1670  23.1052  13.42  4.4  4.4  4.304 × 1015  56  47  −92  238  43  −88  301  87  147  2  0.34  2.0  11  6  0.25  2013  09 26  02:34:36.34  38.3019  22.1353  8.39  3.7  3.8  7.233 × 1014  261  25  −103  95  65  −84  17  69  181  20  0.81  2.5  6  6  0.13  2013  09 26  05:25:12.02  38.2999  22.1292  8.85  3.1  3.1  6.028 × 1013  246  21  −121  99  73  −79  26  61  180  27  0.40  2.5  5  12  0.21  2013  10 22  03:38:57.90  38.3669  21.8797  8.19  3.1  3.1  9.891 × 1013  131  59  −13  227  79  −148  93  30  355  13  0.76  2.7  6  13  0.22  2013  12 09  08:59:35.62  38.3807  21.7454  14.54  3.7  3.6  3.308 × 1014  64  47  −74  221  45  −106  47  78  143  1  0.54  1.7  7  6  0.19  2013  12 22  18:04:02.94  37.8548  22.7335  13.74  3.5  3.6  3.080 × 1014  293  36  −82  103  54  −96  349  80  197  9  0.23  1.4  6  5  0.29  2014  01 24  22:08:48.30  38.3374  21.9980  7.91  3.8  3.8  6.244 × 1014  311  49  −65  96  47  −115  291  72  24  1  0.48  3.6  9  9  0.09  2014  01 29  09:14:23.47  38.3411  21.9822  8.48  3.9  4.1  1.637 × 1015  306  52  −72  98  41  −112  273  75  24  5  0.72  5.6  7  8  0.06  2014  01 29  18:23:44.88  38.342  21.9804  8.47  3.1  3.3  1.31 × 1014  310  60  −66  88  38  −125  264  66  23  12  0.53  6.3  6  15  0.11  2014  01 30  23:48:14.98  38.3857  21.8672  9.04  3.7  3.7  4.311 × 1014  231  26  −132  96  71  −72  31  60  172  24  0.57  2.9  7  11  0.22  2014  02 04  18:19:32.44  38.3397  21.9749  8.94  3.4  3.5  2.501 × 1014  311  58  −57  81  45  −131  275  62  18  7  0.63  6.8  6  9  0.06  2014  02 04  22:49:01.50  38.3339  21.9769  8.67  3.9  3.9  7.897 × 1014  111  45  −93  296  45  −87  282  88  23  0  0.73  5.1  7  9  0.04  2014  02 07  01:21:53.22  38.3144  21.7066  16.29  4.3  4.2  2.221 × 1015  303  77  −41  44  51  −163  255  37  359  17  0.65  2.1  9  12  0.28  2014  02 12  07:41:01.26  37.9327  22.5926  11.70  3.5  3.5  2.315 × 1014  264  29  −109  105  63  −80  36  70  188  18  0.13  2.1  5  6  0.22  2014  02 28  22:13:55.08  38.1975  22.5207  8.14  3.5  3.7  3.920 × 1014  300  33  −63  88  61  −107  323  69  190  14  0.24  2.1  8  9  0.15  2014  03 21  18:35:49.92  38.4122  22.4547  10.21  4.0  3.9  7.537 × 1014  25  41  −171  288  84  −49  234  37  347  27  0.51  2.0  10  11  0.27  2014  04 07  20:15:11.86  38.3348  21.8022  9.29  3.2  3.3  1.01 × 1014  232  25  −140  105  74  −70  41  57  179  26  0.74  3.5  4  11  0.14  2014  04 10  17:40:45.16  37.9305  22.5980  10.47  3.5  3.5  2.577 × 1014  110  48  −78  273  43  −103  84  81  192  3  0.12  1.7  5  8  0.25  2014  04 17  07:04:04.56  38.4092  22.4625  9.57  3.7  3.8  5.569 × 1014  281  64  −56  44  42  −138  237  57  347  12  0.20  1.9  10  20  0.28  2014  04 18  05:07:36.93  38.4223  21.8443  11.25  4.2  3.9  7.888 × 1014  102  86  −72  204  18  −168  30  46  176  39  0.63  3.0  7  13  0.33  2014  05 10  03:04:50.13  38.4164  22.4471  9.99  4.2  4.1  1.889 × 1015  286  69  −64  53  33  −138  232  58  357  19  0.31  2.2  9  11  0.35  2014  05 11  17:34:06.24  38.4361  21.6997  15.02  3.6  3.6  2.879 × 1014  38  78  173  130  83  12  264  3  354  13  0.73  2.7  8  8  0.27  2014  06 08  15:10:51.81  38.3260  22.0525  4.30  4.3  4.2  2.506 × 1015  105  46  −84  276  45  −97  95  85  191  0  0.53  2.1  12  4  0.09  2014  06 10  02:14:30.72  38.3332  22.062  8.76  3.3  3.5  1.96 × 1014  95  46  −91  277  44  −89  328  89  186  1  0.30  2.5  8  7  0.14  2014  06 10  22:52:42.08  38.3315  22.0668  8.15  3.6  3.5  2.196 × 1014  272  57  −100  110  34  −75  154  76  9  12  0.51  2.2  5  12  0.18  2014  06 20  01:53:28.78  38.323  22.0492  8.32  3.3  3.4  1.754 × 1014  112  41  −90  291  49  −90  200  86  22  4  0.39  4.3  8  5  0.07  2014  06 25  09:21:41.85  38.3597  21.7543  17.93  4.2  4.1  1.605 × 1015  197  69  −136  88  50  −28  60  45  318  12  0.40  2.1  9  14  0.29  2014  06 27  00:47:23.63  38.3852  21.9995  9.44  3.0  3.2  8.258 × 1013  325  31  −53  104  66  −110  341  64  209  19  0.49  2.6  7  9  0.35  2014  07 30  07:56:35.32  38.3487  21.8156  9.74  3.4  3.4  1.877 × 1014  239  24  −125  97  70  −76  29  62  176  24  0.40  2.5  10  9  0.16  2014  08 09  22:22:24.28  38.3603  21.8744  8.51  3.0  3.0  4.529 × 1013  236  39  −120  93  57  −67  53  69  167  9  0.56  2.9  4  15  0.17  2014  08 12  04:06:16.20  38.3992  22.5064  10.05  3.4  3.4  1.462 × 1014  255  30  −101  87  60  −84  14  74  173  15  0.56  1.9  6  5  0.24  2014  08 28  04:11:12.25  38.4129  22.4655  10.62  3.3  3.4  1.451 × 1014  302  65  −61  69  38  −136  254  59  11  15  0.70  3.1  6  21  0.10  2014  09 03  00:58:47.98  38.3379  21.9031  6.85  3.5  3.8  5.454 × 1014  78  18  −91  259  72  −90  169  63  348  27  0.36  4.7  5  9  0.08  2014  09 19  09:33:24.85  38.3620  21.8255  8.76  3.5  3.7  4.038 × 1014  274  53  −65  56  44  −119  243  69  346  5  0.41  3.1  11  6  0.12  2014  09 19  15:35:08.84  38.3687  21.8372  10.27  4.1  4.1  1.619 × 1015  86  54  −88  262  37  −93  7  81  174  9  0.60  2.8  8  4  0.11  2014  09 21  00:43:39.42  38.3477  21.8381  9.50  4.6  4.8  1.780 × 1016  70  47  −102  268  44  −77  269  81  169  2  0.74  4.9  10  3  0.04  2014  09 21  01:13:26.45  38.3637  21.8235  9.25  4.0  4.3  3.008 × 1015  271  42  −78  74  49  −101  283  81  172  3  0.70  2.9  11  5  0.08  2014  09 25  02:04:24.34  38.3511  21.8079  10.52  3.7  3.9  9.637 × 1014  269  55  −82  76  35  −101  206  78  354  10  0.39  4.6  12  7  0.03  2014  09 26  04:33:32.17  38.3447  21.9647  9.38  3.8  3.9  8.386 × 1014  293  51  −73  88  41  −110  260  76  11  5  0.56  2.4  9  7  0.03  2014  10 30  06:09:09.20  38.1461  22.6267  9.18  3.7  3.9  8.056 × 1014  293  42  −70  87  51  −107  298  76  189  5  0.19  2.6  7  2  0.09  2014  11 07  17:12:59.68  38.2890  22.1226  8.51  4.8  4.9  3.261 × 1016  270  23  −96  96  67  −88  10  67  184  22  0.75  3.0  13  3  0.07  2014  12 09  17:08:29.00  38.4047  22.2319  14.68  3.6  3.5  1.890 × 1014  122  23  −94  307  67  −88  220  68  36  22  0.48  2.0  8  5  0.30  View Large APPENDIX B: CHARACTERISTICS OF EARTHQUAKES CLUSTERS Table B1. Characteristics of earthquakes clusters: serial number (ID), where W is for clusters that occurred on the western part of Corinth Gulf and E for those on the eastern part, start and end time, number of events (N), maximum magnitude in each cluster (Mmax), mean epicentral coordinates (Longitude and Latitude), mean depth of the segment, strike, dip, fault trace at the given depth, the subregion (see Table 2) and the absolute difference in strike (ΔS) and dip (ΔD) from the corresponding TSMT solution. ID  Start  End  N  Mmax  Longitude (°N)  Latitude (°E)  Depth (km)  Strike (°)  Dip (°)  Fault trace (°N, °E)  Subregion  ΔS (°)  ΔD (°)  W01  2008/07/19 00:21:22  2008/07/30 10:54:24  113  3.7  21.9046  38.2919  7  100  40  21.8887–21.9171, 38.2935–38.2874  02  24  8  W02  2009/01/10 13:31:41  2009/01/13 05:05:03  27  3.1  22.0364  38.3089  8  280  50  22.0235–22.0493, 38.3108–38.3067  03  3  23  W03  2009/03/10 00:18:42  2009/03/16 20:46:13  56  3.9  21.8442  38.3513  8.5  255  45  21.8301–21.8537, 38.3544–38.3590  02  8  5  W04  2009/06/23 10:11:21  2009/07/10 03:45:52  72  3.7  22.0621  38.3064  8  290  45  22.0390–22.0801, 38.3149–38.3006  03  13  18  W05  2010/05/06 10:08:17  2010/05/27 03:11:32  229  3.8  21.8318  38.4289  10  270  55  21.8178–21.8556, 38.4278  02  7  15  W06  2011/02/01 19:52:23  2011/02/03 17:58:56  19  3.5  21.7981  38.3903  10.5  270  50  21.7908–21.8037, 38.3920  02  7  10  W07  2011/02/04 11:05:46  2011/02/07 15:27:39  109  3.5  22.0236  38.4158  8.5  290  65  22.0127–22.0337, 38.4208–38.4140  03  13  38  W08  2011/02/19 19:04:32  2011/02/25 19:26:46  103  3.7  21.6590  38.4988  14.5  75  84  21.6513–21.6715, 38.4951–38.5024  01  12  8  W09  2011/03/19 03:33:33  2011/03/24 06:33:46  25  2.9  21.8636  38.3933  8.5  255  60  21.8487–21.8791, 38.392–38.398  02  8  17  W10  2011/07/23 10:20:18  2011/08/11 04:15:37  279  4.3  21.7514  38.3149  9  240  60  21.7371–21.7828, 38.3033–38.3249  02  23  17  W11  2011/08/30 05:09:32  2011/09/21 03:40:04  56  3.4  21.7599  38.3157  9.5  290  55  21.7452–21.7726, 38.3163–38.3098  02  17  12  W12  2011/09/18 05:43:49  2011/09/21 01:29:14  91  3.3  21.8316  38.2193  7.5  220  50  21.8252–21.8403, 38.2101–38.2253  02  43  7  W13  2011/10/01 21:06:19  2011/10/03 03:02:14  10  2.4  21.7653  38.3245  8.5  110  45  21.7589–21.7698, 38.3270–38.3227  02  34  3  W14  2011/10/04 18:28:25  2011/10/05 05:26:43  10  2.3  21.8300  38.2168  8  270  40  21.8259–21.8346, 38.2171  02  7  3  W15  2011/11/16 09:04:18  2011/11/20 00:15:24  40  2.2  21.8452  38.4131  10.5  270  50  21.8422–21.8551, 38.4140  02  7  7  W16  2011/11/30 03:16:36  2011/12/01 07:34:25  20  1.7  21.8826  38.2647  7.5  270  30  21.8775–21.8860, 38.2616  02  7  13  W17  2011/12/19 23:41:38  2011/12/22 12:22:22  25  2.3  22.0413  38.3417  8.5  280  65  22.0324–22.0454, 38.3422–38.3405  03  3  38  W18  2012/01/17 17:13:01  2012/01/21 22:15:16  62  3.1  21.8365  38.3795  9  270  65  21.8294–21.8474, 38.378  02  7  22  W19  2012/02/25 11:01:13  2012/02/27 00:53:16  11  2.3  22.0812  38.3126  8.5  290  60  22.0762–22.0804, 38.3126–38.3093  03  13  33  W20  2012/03/11 23:49:25  2012/03/24 05:44:52  37  2.8  21.6914  38.5893  10  110  30  21.690–21.7008, 38.5903–38.585  02  34  18  W21  2012/04/15 21:03:53  2012/04/24 17:07:35  91  3.8  22.1226  38.2934  8.0  280  60  22.1059–22.1318, 38.296–38.2908  03  3  33  W22  2012/06/12 08:34:06  2012/06/14 03:08:59  23  2.1  22.0666  38.2721  10.5  110  55  22.0596–22.0705, 38.2720–38.2685  03  17  8  W23  2012/06/21 15:37:15  2012/06/28 22:24:51  18  2.9  22.0951  38.3029  8.0  290  55  22.0822–22.0992, 38.3123– 38.3005  03  13  28  W24  2012/06/24 02:14:30  2012/06/27 20:42:11  15  1.7  21.8633  38.4957  15  90  40  21.8614–21.8700, 38.4933  02  14  8  W25  2012/08/12 08:07:46  2012/08/23 18:40:45  64  3.1  22.1127  38.2953  8.25  280  60  22.1004–22.1356, 38.2977–38.290  03  3  33  W26  2012/09/06 01:43:47  2012/09/18 02:03:35  32  3.1  21.8616  38.3603  8.7  290  50  21.8577–21.8757, 38.362–38.358  02  27  7  W27  2013/01/27 15:47:35  2013/01/30 11:44:12  30  3.2  38.3017  23.1105  8.5  290  60  22.1363–22.1563, 38.3239–38.3160  03  13  33  W28  2013/01/28 08:43:15  2013/02/14 13:09:31  44  3.6  22.1469  38.3173  8.5  290  60  22.1018–22.1200, 38.3066–38.2988  03  13  33  W29  2013/03/20 22:41:31  2013/03/24 18:27:53  23  3.3  22.0391  38.3229  8.0  280  40  22.0302–22.0448, 38.3217–38.3200  03  3  13  W30  2013/06/14 21:09:36  2013/06/19 05:52:13  71  1.9  22.1730  38.2420  8.5  260  45  22.1594–22.1913, 38.2382–38.2441  04  11  9  W31  2013/07/05 17:23:49  2013/07/07 10:15:56  53  2.7  22.0629  38.3277  8.5  90  50  22.0497–22.0686, 38.3268  03  3  13  W32  2013/09/09 16:26:48  2013/09/14 00:00:09  131  2.8  22.0326  38.3984  8  110  50  22.0215–22.0395, 38.4011–38.3952  03  17  13  W33  2013/10/22 03:38:57  2013/10/29 23:06:54  29  3.1  21.8812  38.3682  7.5  110  30  21.8909–21.9045, 38.3753–38.3710  02  34  18  W34  2013/10/26 09:26:47  2013/11/12 12:25:18  249  3.1  22.1119  38.2331  10.5  280  45  22.1036–22.1209, 38.2328–38.2307  04  9  9  W35  2013/10/26 09:33:11  2013/10/28 11:27:31  22  3.1  21.8983  38.3753  8  110  40  21.8718–21.8854, 38.3689–38.3641  02  34  8  W36  2013/12/02 21:02:46  2013/12/15 18:27:06  79  2.8  21.8422  38.3267  8  270  60  21.820–21.860, 38.328  02  7  17  W37  2014/01/07 23:41:30  2014/01/22 06:09:05  53  2.9  22.0175  38.3872  7.5  280  60  22.0133–22.0251, 38.3885–38.3862  03  3  33  W38  2014/01/16 22:53:58  2014/01/26 07:49:42  37  2.6  21.9802  38.3465  8.25  280  40  21.9653–21.9880, 38.3495–38.3459  03  3  13  W39  2014/06/08 00:32:41  2014/06/24 19:34:06  132  4.3  22.0545  38.3221  8.5  280  50  22.0441–22.0627, 38.3248–38.3216  03  3  23  W40  2014/06/08 16:49:41  2014/06/17 13:30:32  67  3.6  22.0645  38.3328  8.5  270  50  22.0524–22.0731, 38.3313  03  7  23  W41  2014/07/25 09:56:50  2014/07/29 06:08:57  13  2.2  22.0862  38.3013  8.5  280  50  22.0808–22.0931, 38.3021–38.3005  03  3  23  W42  2014/08/23 21:00:15  2014/08/27 21:47:26  18  2.4  22.0749  38.3079  8.5  280  45  22.0683–22.0791, 38.3107–38.3090  03  3  18  W43  2014/09/18 05:43:21  2014/09/28 23:34:54  170  4.6  21.8181  38.3573  10  250  55  21.796–21.8551, 38.349–38.36  02  13  12  W44  2014/11/07 17:12:59  2014/12/02 00:33:13  270  4.8  22.1380  38.2745  7.5  270  35  22.12–22.16, 38.275  03  7  8  W45  2014/11/24 12:32:39  2014/11/27 04:52:27  14  2.5  22.0902  38.3046  8.5  270  45  22.0765–22.0960, 38.3039–38.3005  03  7  18  W46  2014/12/09 14:06:05  2014/12/15 02:27:30  22  2.2  22.0705  38.3035  8.0  290  40  22.052–22.0762, 38.3052–38.2930  03  13  13  W47  2014/12/17 18:20:15  2014/12/24 22:09:10  28  2.1  22.0817  38.2991  8.25  280  50  22.0770–22.0967, 38.3005–38.2971  03  3  23  E01  2009/05/16 12:56:19  2009/05/22 17:13:19  43  4.4  22.6764  38.1230  9.0  280  50  22.6542–22.7014, 38.1245–38.1143  06  18  23  E02  2013/06/10 04:53:57  2013/06/29 02:55:05  332  3.5  23.1999  38.1615  8.0  60  55  23.1896–23.2193, 38.1484–38.1606  08  4  7  ID  Start  End  N  Mmax  Longitude (°N)  Latitude (°E)  Depth (km)  Strike (°)  Dip (°)  Fault trace (°N, °E)  Subregion  ΔS (°)  ΔD (°)  W01  2008/07/19 00:21:22  2008/07/30 10:54:24  113  3.7  21.9046  38.2919  7  100  40  21.8887–21.9171, 38.2935–38.2874  02  24  8  W02  2009/01/10 13:31:41  2009/01/13 05:05:03  27  3.1  22.0364  38.3089  8  280  50  22.0235–22.0493, 38.3108–38.3067  03  3  23  W03  2009/03/10 00:18:42  2009/03/16 20:46:13  56  3.9  21.8442  38.3513  8.5  255  45  21.8301–21.8537, 38.3544–38.3590  02  8  5  W04  2009/06/23 10:11:21  2009/07/10 03:45:52  72  3.7  22.0621  38.3064  8  290  45  22.0390–22.0801, 38.3149–38.3006  03  13  18  W05  2010/05/06 10:08:17  2010/05/27 03:11:32  229  3.8  21.8318  38.4289  10  270  55  21.8178–21.8556, 38.4278  02  7  15  W06  2011/02/01 19:52:23  2011/02/03 17:58:56  19  3.5  21.7981  38.3903  10.5  270  50  21.7908–21.8037, 38.3920  02  7  10  W07  2011/02/04 11:05:46  2011/02/07 15:27:39  109  3.5  22.0236  38.4158  8.5  290  65  22.0127–22.0337, 38.4208–38.4140  03  13  38  W08  2011/02/19 19:04:32  2011/02/25 19:26:46  103  3.7  21.6590  38.4988  14.5  75  84  21.6513–21.6715, 38.4951–38.5024  01  12  8  W09  2011/03/19 03:33:33  2011/03/24 06:33:46  25  2.9  21.8636  38.3933  8.5  255  60  21.8487–21.8791, 38.392–38.398  02  8  17  W10  2011/07/23 10:20:18  2011/08/11 04:15:37  279  4.3  21.7514  38.3149  9  240  60  21.7371–21.7828, 38.3033–38.3249  02  23  17  W11  2011/08/30 05:09:32  2011/09/21 03:40:04  56  3.4  21.7599  38.3157  9.5  290  55  21.7452–21.7726, 38.3163–38.3098  02  17  12  W12  2011/09/18 05:43:49  2011/09/21 01:29:14  91  3.3  21.8316  38.2193  7.5  220  50  21.8252–21.8403, 38.2101–38.2253  02  43  7  W13  2011/10/01 21:06:19  2011/10/03 03:02:14  10  2.4  21.7653  38.3245  8.5  110  45  21.7589–21.7698, 38.3270–38.3227  02  34  3  W14  2011/10/04 18:28:25  2011/10/05 05:26:43  10  2.3  21.8300  38.2168  8  270  40  21.8259–21.8346, 38.2171  02  7  3  W15  2011/11/16 09:04:18  2011/11/20 00:15:24  40  2.2  21.8452  38.4131  10.5  270  50  21.8422–21.8551, 38.4140  02  7  7  W16  2011/11/30 03:16:36  2011/12/01 07:34:25  20  1.7  21.8826  38.2647  7.5  270  30  21.8775–21.8860, 38.2616  02  7  13  W17  2011/12/19 23:41:38  2011/12/22 12:22:22  25  2.3  22.0413  38.3417  8.5  280  65  22.0324–22.0454, 38.3422–38.3405  03  3  38  W18  2012/01/17 17:13:01  2012/01/21 22:15:16  62  3.1  21.8365  38.3795  9  270  65  21.8294–21.8474, 38.378  02  7  22  W19  2012/02/25 11:01:13  2012/02/27 00:53:16  11  2.3  22.0812  38.3126  8.5  290  60  22.0762–22.0804, 38.3126–38.3093  03  13  33  W20  2012/03/11 23:49:25  2012/03/24 05:44:52  37  2.8  21.6914  38.5893  10  110  30  21.690–21.7008, 38.5903–38.585  02  34  18  W21  2012/04/15 21:03:53  2012/04/24 17:07:35  91  3.8  22.1226  38.2934  8.0  280  60  22.1059–22.1318, 38.296–38.2908  03  3  33  W22  2012/06/12 08:34:06  2012/06/14 03:08:59  23  2.1  22.0666  38.2721  10.5  110  55  22.0596–22.0705, 38.2720–38.2685  03  17  8  W23  2012/06/21 15:37:15  2012/06/28 22:24:51  18  2.9  22.0951  38.3029  8.0  290  55  22.0822–22.0992, 38.3123– 38.3005  03  13  28  W24  2012/06/24 02:14:30  2012/06/27 20:42:11  15  1.7  21.8633  38.4957  15  90  40  21.8614–21.8700, 38.4933  02  14  8  W25  2012/08/12 08:07:46  2012/08/23 18:40:45  64  3.1  22.1127  38.2953  8.25  280  60  22.1004–22.1356, 38.2977–38.290  03  3  33  W26  2012/09/06 01:43:47  2012/09/18 02:03:35  32  3.1  21.8616  38.3603  8.7  290  50  21.8577–21.8757, 38.362–38.358  02  27  7  W27  2013/01/27 15:47:35  2013/01/30 11:44:12  30  3.2  38.3017  23.1105  8.5  290  60  22.1363–22.1563, 38.3239–38.3160  03  13  33  W28  2013/01/28 08:43:15  2013/02/14 13:09:31  44  3.6  22.1469  38.3173  8.5  290  60  22.1018–22.1200, 38.3066–38.2988  03  13  33  W29  2013/03/20 22:41:31  2013/03/24 18:27:53  23  3.3  22.0391  38.3229  8.0  280  40  22.0302–22.0448, 38.3217–38.3200  03  3  13  W30  2013/06/14 21:09:36  2013/06/19 05:52:13  71  1.9  22.1730  38.2420  8.5  260  45  22.1594–22.1913, 38.2382–38.2441  04  11  9  W31  2013/07/05 17:23:49  2013/07/07 10:15:56  53  2.7  22.0629  38.3277  8.5  90  50  22.0497–22.0686, 38.3268  03  3  13  W32  2013/09/09 16:26:48  2013/09/14 00:00:09  131  2.8  22.0326  38.3984  8  110  50  22.0215–22.0395, 38.4011–38.3952  03  17  13  W33  2013/10/22 03:38:57  2013/10/29 23:06:54  29  3.1  21.8812  38.3682  7.5  110  30  21.8909–21.9045, 38.3753–38.3710  02  34  18  W34  2013/10/26 09:26:47  2013/11/12 12:25:18  249  3.1  22.1119  38.2331  10.5  280  45  22.1036–22.1209, 38.2328–38.2307  04  9  9  W35  2013/10/26 09:33:11  2013/10/28 11:27:31  22  3.1  21.8983  38.3753  8  110  40  21.8718–21.8854, 38.3689–38.3641  02  34  8  W36  2013/12/02 21:02:46  2013/12/15 18:27:06  79  2.8  21.8422  38.3267  8  270  60  21.820–21.860, 38.328  02  7  17  W37  2014/01/07 23:41:30  2014/01/22 06:09:05  53  2.9  22.0175  38.3872  7.5  280  60  22.0133–22.0251, 38.3885–38.3862  03  3  33  W38  2014/01/16 22:53:58  2014/01/26 07:49:42  37  2.6  21.9802  38.3465  8.25  280  40  21.9653–21.9880, 38.3495–38.3459  03  3  13  W39  2014/06/08 00:32:41  2014/06/24 19:34:06  132  4.3  22.0545  38.3221  8.5  280  50  22.0441–22.0627, 38.3248–38.3216  03  3  23  W40  2014/06/08 16:49:41  2014/06/17 13:30:32  67  3.6  22.0645  38.3328  8.5  270  50  22.0524–22.0731, 38.3313  03  7  23  W41  2014/07/25 09:56:50  2014/07/29 06:08:57  13  2.2  22.0862  38.3013  8.5  280  50  22.0808–22.0931, 38.3021–38.3005  03  3  23  W42  2014/08/23 21:00:15  2014/08/27 21:47:26  18  2.4  22.0749  38.3079  8.5  280  45  22.0683–22.0791, 38.3107–38.3090  03  3  18  W43  2014/09/18 05:43:21  2014/09/28 23:34:54  170  4.6  21.8181  38.3573  10  250  55  21.796–21.8551, 38.349–38.36  02  13  12  W44  2014/11/07 17:12:59  2014/12/02 00:33:13  270  4.8  22.1380  38.2745  7.5  270  35  22.12–22.16, 38.275  03  7  8  W45  2014/11/24 12:32:39  2014/11/27 04:52:27  14  2.5  22.0902  38.3046  8.5  270  45  22.0765–22.0960, 38.3039–38.3005  03  7  18  W46  2014/12/09 14:06:05  2014/12/15 02:27:30  22  2.2  22.0705  38.3035  8.0  290  40  22.052–22.0762, 38.3052–38.2930  03  13  13  W47  2014/12/17 18:20:15  2014/12/24 22:09:10  28  2.1  22.0817  38.2991  8.25  280  50  22.0770–22.0967, 38.3005–38.2971  03  3  23  E01  2009/05/16 12:56:19  2009/05/22 17:13:19  43  4.4  22.6764  38.1230  9.0  280  50  22.6542–22.7014, 38.1245–38.1143  06  18  23  E02  2013/06/10 04:53:57  2013/06/29 02:55:05  332  3.5  23.1999  38.1615  8.0  60  55  23.1896–23.2193, 38.1484–38.1606  08  4  7  View Large APPENDIX C: SPATIAL DISTRIBUTION OF ERRORS Figure C1. View largeDownload slide Spatial distribution of errors in (a) and (b) X, (c) and (d) Y and (e) and (f) Z-direction for the different parts of Corinth Gulf. Errors are in metres. Figure C1. View largeDownload slide Spatial distribution of errors in (a) and (b) X, (c) and (d) Y and (e) and (f) Z-direction for the different parts of Corinth Gulf. Errors are in metres. © The Author(s) 2017. Published by Oxford University Press on behalf of The Royal Astronomical Society.

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Geophysical Journal InternationalOxford University Press

Published: Feb 1, 2018

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