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King, Chi-Yu; Zhang, Wei; Zhang, Zhaocheng
doi: 10.1007/s00024-006-0049-7pmid: N/A
Active faults are commonly associated with spatially anomalously high concentrations of soil gases such as carbon dioxide and Rn, suggesting that they are crustal discontinuities with a relatively high vertical permeability through which crustal and subcrustal gases may preferably escape towards the earth's surface. Many earthquake-related hydrologic and geochemical temporal changes have been recorded, mostly along active faults especially at fault intersections, since the 1960s. The reality of such changes is gradually ascertained and their features well delineated and fairly understood. Some coseismic changes recorded in ``near field'' are rather consistent with poroelastic dislocation models of earthquake sources, whereas others are attributable to near-surface permeability enhancement. In addition, coseismic (and postseismic) changes were recorded for many moderate to large earthquakes at certain relatively few ``sensitive sites'' at epicentral distances too large (larger for larger earthquakes, up to 1000 km or more for magnitude 8) to be explained by the poroelastic models. They are probably triggered by seismic shaking. The sensitivity of different sites can be greatly different, even when separated only by meters. The sensitive sites are usually located on or near active faults, especially their intersections and bends, and characterized by some near-critical hydrologic or geochemical condition (e.g., permeability that can be greatly increased by a relatively small seismic shaking or stress increase). Coseismic changes recorded for different earthquakes at a sensitive site are usually similar, regardless of the earthquakes' location and focal mechanism. The sensitivity of a sensitive site may change with time. Also pre-earthquake changes were observed hours to years before some destructive earthquakes at certain sensitive sites, some at large epicentral distances, although these changes are relatively few and less certain. Both long-distance coseismic and preseismic changes call for more realistic models than simple elastic dislocation for explanation. Such models should take into consideration the heterogeneity of the crust where stress is concentrated at certain weak points (sensitive sites) along active faults such that the stress condition is near a critical level prior to the occurrence of the corresponding earthquakes. To explain the preseismic changes, the models should also assume a broad-scaled episodically increasing strain field.
Ohno, Masao; Sato, Tsutomu; Notsu, Kenji; Wakita, Hiroshi; Ozawa, Kunio
doi: 10.1007/s00024-006-0041-2pmid: N/A
Anomalous water level changes were observed at two wells associated with seismic swarm activity off Izu Peninsula on March, 1997. These are coseismic water level drops followed by gradual postseismic water level rise at the time of large earthquakes during the swarm activity. The post-seismic water level rises, which can be fitted by an exponential function with a time constant of about six hours, are explained in terms of the horizontal pressure diffusion due to the pressure gradient in the aquifer induced by the coseismic static strain.
Kitagawa, Yuichi; Koizumi, Naoji; Ohtani, Ryu; Watanabe, Kunihiko; Itaba, Satoshi
doi: 10.1007/s00024-006-0048-8pmid: N/A
To understand the detailed process of fault activity, aseismic slip may play a crucial role. Aseismic slip of inland faults in Japan is not well known, except for that related to the Atotsugawa fault. To know whether aseismic slip does not occur, or is merely not detected, is an important question. The National Institute of Advanced Industrial Science and Technology constructed an observation site near Yasutomi fault, a part of the Yamasaki fault system, and has collected data on the crustal strain field, groundwater pressures, and crustal movement using GPS. In a departure from the long-term trend, a transient change of the crustal strain field lasting a few months was recorded. It indicated the possibility of an aseismic slip event. Furthermore, analyses of data from the extensometers at Yasutomi and Osawa observation vaults of Kyoto University, as well as GPS data from the Geographical Survey Institute (GEONET), revealed unsteady crustal strain changes. All data could be explained by local, left-lateral, aseismic slip of the order of 1 mm in the shallow part of the Yasutomi fault.
Song, S. R.; Ku, W. Y.; Chen, Y. L.; Liu, C. M.; Chen, H. F.; Chan, P. S.; Chen, Y. G.; Yang, T. F.; Chen, C. H.; Liu, T. K.; Lee, M.
doi: 10.1007/s00024-006-0046-xpmid: N/A
Water samples from both hot and artesian springs in Kuantzeling in west-central Taiwan have been collected on a regular basis from July 15, 1999 to the end of August 2001 to measure cation and anion concentrations as a tool to detect major earthquake precursors. The data identify chloride and sulfate ion anomalies few days prior to major quakes and lasting a few days afterward. These anomalies are characterized by increases in Cl- concentrations from 34.9% to 41.2% and 71.5% to 138.1% as well as increases in SO4 2- concentrations from 232.7% to 276.8% and 100.0% to 155.1% above the means in both hot and artesian springs. The occurrence of these anomalies is probably explained first as stress/strain-induced pressure changes in the subsurface water systems which then generate precursory limited geochemical discharges at the levels of subsurface reservoirs. Therefore, finally leading to the mixing of previously separated subsurface water bodies occurs. This suggests that the hot and artesian springs in the Kuantzeling area are possible ideal sites for recording strain changes serving well as earthquake precursors.
Yang, T.; Fu, C.-C.; Walia, V.; Chen, C.-H.; Chyi, L.; Liu, T.-K.; Song, S.-R.; Lee, M.; Lin, C.-W.; Lin, C.-C.
doi: 10.1007/s00024-006-0040-3pmid: N/A
Gas variations of many mud volcanoes and hot springs distributed along the tectonic sutures in southwestern Taiwan are considered to be sensitive to the earthquake activity. Therefore, a multi-parameter automatic gas station was built on the bank of one of the largest mud-pools at an active fault zone of southwestern Taiwan, for continuous monitoring of CO2, CH4, N2 and H2O, the major constituents of its bubbling gases. During the year round monitoring from October 2001 to October 2002, the gas composition, especially, CH4 and CO2, of the mud pool showed significant variations. Taking the CO2/CH4 ratio as the main indicator, anomalous variations can be recognized from a few days to a few weeks before earthquakes and correlated well with those with a local magnitude >4.0 and local intensities >2. It is concluded that the gas composition in the area is sensitive to the local crustal stress/strain and is worthy to conduct real-time monitoring for the seismo-geochemical precursors.
Walia, Vivek; Virk, Hardev Singh; Bajwa, Bikramjit Singh
doi: 10.1007/s00024-006-0044-zpmid: N/A
The N-W Himalaya was rocked by a few major and many minor earthquakes. Two major earthquakes in Garhwal Himalaya: Uttarkashi earthquake of magnitude Ms= 7.0 (mb = 6.6) on October 20, 1991 in Bhagirthi valley and Chamoli earthquake of Ms= 6.5 (mb = 6.8) on March 29, 1999 in the Alaknanda valley and one in Himachal Himalaya: Chamba earthquake of magnitude 5.1 on March 24, 1995 in Chamba region, were recorded during the last decade and correlated with radon anomalies. The helium anomaly for Chamoli earthquake was also recorded and the Helium/Radon ratio model was tested on it. The precursory nature of radon and helium anomalies is a strong indicator in favor of geochemical precursors for earthquake prediction and a preliminary test for the Helium/Radon ratio model.
Toutain, Jean-Paul; Munoz, Margot; Pinaud, Jean-Louis; Levet, Stéphanie; Sylvander, Matthieu; Rigo, Alexis; Escalier, Jocelyne
doi: 10.1007/s00024-006-0047-9pmid: N/A
Groundwater coseismic transient anomalies are evidenced and characterized by modelling the mixing function F characteristic of the groundwater dynamics in the Ogeu (western French Pyrénées) seismic context. Investigations of water-rock interactions at Ogeu indicate that these mineral waters from sedimentary environments result from the mixing of deep waters with evaporitic signature with surficial karstic waters. A 3-year hydrochemical monitoring of Ogeu springwater evidences that using arbitrary thresholds constituted by the mean ± 1 or 2σ, as often performed in such studies, is not a suitable approach to characterize transient anomalies. Instead, we have used a mixing function F calculated with chemical elements, which display a conservative behavior not controlled by the precipitation of a mineral phase. F is processed with seismic energy release (E s ) and effective rainfalls (R). Linear impulse responses of F to E s and R have been calculated. Rapid responses (10 days) to rainwater inputs are evidenced, consisting in the recharge of the shallow karstic reservoir by fresh water. Complex impulse response of F to microseismic activity is also evidenced. It consists in a 2-phase hydrologic signal, with an inflow of saline water in the shallow reservoir with a response delay of 10 days, followed by an inflow of karstic water with a response delay of 70 days, the amount being higher than the saline inflow. Such a process probably results from changes in volumetric strain with subsequent microfracturation transient episodes allowing short inflow of deep salted water in the aquifer. This study demonstrates that groundwater systems in such environments are unstable systems that are highly sensitive to both rainfall inputs and microseismic activity. Impulse responses calculation of F to E s is shown to be a powerful tool to identify transient anomalies. Similar processing is suggested to be potentially efficient to detect precursors of earthquakes when long time-series (5 years at least) are available in areas with high seismicity.
Sano, Yuji; Takahata, Naoto; Seno, Tetsuzo
doi: 10.1007/s00024-006-0035-0pmid: N/A
We have collected 34 hot spring and mineral spring gases and waters in the Chugoku and Kansai districts, Southwestern Japan and measured the 3He/4He and 4He/20Ne ratios by using a noble gas mass spectrometer. Observed 3He/4He and 4He/20Ne ratios range from 0.054 Ratm to 5.04 Ratm (where Ratm is the atmospheric 3He/4He ratio of 1.39 × 10−6) and from 0.25 to 36.8, respectively. They are well explained by a mixing of three components, mantle-derived, radiogenic, and atmospheric helium dissolved in water. The 3He/4He ratios corrected for air contamination are low in the frontal arc and high in the volcanic arc regions, which are consistent with data of subduction zones in the literature. The geographical contrast may provide a constraint on the position of the volcanic front in the Chugoku district where it was not well defined by previous works. Taking into account the magma aging effect, we cannot explain the high 3He/4He ratios of the volcanic arc region by the slab melting of the subducting Philippine Sea plate. The other source with pristine mantle material may be required. More precisely, the highest and average 3He/4He ratios of 5.88 Ratm and 3.8±1.6 Ratm, respectively, in the narrow regions near the volcanic front of the Chugoku district are lower than those in Kyushu and Kinki Spot in Southwestern Japan, but close to those in NE Japan. This suggests that the magma source of the former may be related to the subduction of the Pacific plate, in addition to a slight component of melting of the Philippine Sea slab.
Chiodini, Giovanni; Caliro, Stefano; Caramanna, Giorgio; Granieri, Domenico; Minopoli, Carmine; Moretti, Roberto; Perotta, Lavinia; Ventura, Guido
doi: 10.1007/s00024-006-0037-ypmid: N/A
The marine sector surrounding Panarea Island (Aeolian Islands, South Italy) is affected by widespread submarine emissions of CO2 -rich gases and thermal water discharges which have been known since the Roman Age. On November 3rd, 2002 an anomalous degassing event affected the area, probably in response to a submarine explosion. The concentrations of minor reactive gases (CO, CH4 and H2) of samples collected in November and December, 2002 show drastic compositional changes when compared to previous samples collected from the same area in the 1980s. In particular the samples collected after the November 3rd phenomenon display relative increases in H2 and CO and a strong decrease in the CH4 contents, while other gas species show no significant change. The interaction of the original gas with seawater explains the variable contents of CO2, H2S, N2, Ar and He which characterize the different samples, but cannot explain the large variations of CO, CH4 and H2 which are instead compatible with changes in the redox, temperature and pressure conditions of the system. Two models, both implying an increasing input of magmatic fluids are compatible with the observed variations of minor reactive species. In the first one, the input of magmatic fluids drives the hydrothermal system towards atypical (more oxidizing) redox conditions, slowly pressurizing the system up to a critical state. In the second one, the hydrothermal system is flashed by the rising high-T volcanic fluid, suddenly released by a magmatic body at depth. The two models have different implications for volcanic surveillance and risk assessment: In the first case, the November 3rd event may represent both the culmination of a relatively slow process which caused the overpressurization of the hydrothermal system and the beginning of a new phase of quiescence. The possible evolution of the second model is unforeseeable because it is mainly related to the thermal, baric and compositional state of the deep magmatic system that is poorly known.
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