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[en] Complete text of publication follows. The global ionospheric map (GIM) is used to observe variations in the total electron content (TEC) of the global positioning system (GPS) associated with 35 M?6.0 earthquakes occurred in China during a 10-year period of 1 May 1998-30 April 2008. The statistical results indicate that the GPS TEC above the epicenter often pronouncedly decreases on day 3-5 before 17 M?6.3 earthquakes. The GPS TEC of the GIM and electron density profiles probed by six micro satellites of FORMOSAT3/COSMIC (F3/C) are further employed to simultaneously observe seismo-ionospheric anomalies during an Mw 7.9 earthquake near Wenchuan, China on 12 May 2008. It is found that GPS TEC above the forthcoming epicenter anomalously decrease in the afternoon period of day 6 to 4 and in the late evening period of day 3 before the earthquake, but enhance in the afternoon of day 3 before the earthquake. The spatial distributions of the anomalous and extreme reductions and enhancements indicate that the earthquake preparation area is about 1650km and 2850km from the epicenter in the latitudinal and longitudinal directions, respectively. The F3/C results further show that the ionospheric F2-peak electron density NmF2 and height hmF2 significantly decreases approximately 40% and descends about 50-80km, respectively, when the GPS TEC anomalously reduces.
[en] Complete text of publication follows. We modeled the source field of the 1999 Taiwan Chi-Chi earthquake (MW7.6) using the geomagnetic data at Lunping (LNP), Taiwan, Geomagnetic Observatory situated 100 km from the epicenter. This large inland thrust earthquake produced a surface break more than 80 km long along the Chelungpu fault. First, we developed a 3D model consistent with the surface rupture and the focal depth data. Next, we applied the finite difference method for the 3-D case to construct the theoretic induction arrows. The forward results were compared to the observed one at LNP station. The optimum model was set finally when the variance between the theoretic and observed data is small enough. We find that the source dimension is about 30 x 30 x 80 km3.
[en] The Kachchh rift basin is located on the western continental margin of India and has a history of experiencing large to moderate intraplate earthquakes with M ≥ 5. During the past two centuries, two large earthquakes of Mw 7.8 (1819) and Mw 7.7 (2001) have occurred in the Kachchh region, the latter with an epicenter near Bhuj. The aftershock activity of the 2001 Bhuj earthquake is still ongoing with migration of seismicity. Initially, epicenters migrated towards the east and northeast within the Kachchh region but, since 2007, it has also migrated to the south. The triggered faults are mostly within 100 km and some up to 200 km distance from the epicentral area of the mainshock. Most of these faults are trending in E-W direction, and some are transverse. It was noticed that some faults generate earthquakes down to the Moho depth whereas some faults show earthquake activity within the upper crustal volume. The Gedi Fault, situated about 50 km northeast of the 2001 mainshock epicenter, triggered the largest earthquake of Mw 5.6 in 2006. We have carried out detailed seismological studies to evaluate the seismic potential of the Gedi Fault. We have relocated 331 earthquakes by HypoDD to improve upon location errors. Further, the relocated events are used to estimate the b value, p value, and fractal correlation dimension Dc of the fault zone. The present study indicates that all the events along the Gedi Fault are shallow in nature, with focal depths less than 20 km. The estimated b value shows that the Gedi aftershock sequence could be classified as Mogi’s type 2 sequence, and the p value suggests a relatively slow decay of aftershocks. The fault plane solutions of some selected events of Mw > 3.5 are examined, and activeness of the Gedi Fault is assessed from the results of active fault studies as well as GPS and InSAR results. All these results are critically examined to evaluate the material properties and seismic potential of the Gedi Fault that may be useful for seismic hazard assessment in the region.
[en] Several methods have been proposed to study the spatiotemporal correlations between earthquakes. Marsan and co-workers proposed a method based on correlations between all earthquake pairs, without distinction between mainshock and aftershocks, and interpreted their results in terms of a space-time coupling in the triggering process between events. In contrast, we studied the diffusion of aftershocks by analyzing the average distance between a triggered event ('aftershock') and a previous large earthquake (the 'mainshock' which initiated the aftershock sequence). We reply to the comments of Marsan and Bean on our previous paper and discuss the applicability of both methods to unravel the spatiotemporal coupling of earthquake triggering processes
[en] The earthquakes that have occurred around Kiruna in northern Sweden have been studied in detail in order to determine their source characteristics and to understand the pattern of seismic acticity in the region. All earthquakes with magnitude greater than 3.0 (ML) that occurred during the period between 1967 and 1985 in the region bounded by 66.5 degrees - 69 degrees N and 19 degrees - 25 degrees E are studied. Relocated epicenters of the events exhibit a cluster of events in a direction NE - SW at at the western side of the region close to Kiruna, Though, the focal depths of the events are not very well constrained, the relocation results suggest that the events in this cluster might have occurred at focal depths between 15 and 25 km. At the easstern side of the region, the epicenters are roughly aligned along an elongated area trending NNW - SSE. The focal depths of the events in this area tend to be shallow and are probably in the upper crust at the depths range from 5 to 16 km. The earthquakes studied show nearly constant source radii of about 0.4 - 0.6 km over the seismic moment range 1020 to 1021 dyne-cm. Consequently, the events studied are characterized by a steadily incresing stress drop relative to increasing seismic moment. The source mechanisms obtained for the two largest earthquakes suggest that the mechanisms are dominated by the normal faultings on the near-vertical fault planes trending N - S to NE - SW. (With 26 refs.) (authors)
[en] The Valais is the most seismically active region of Switzerland. Strong damaging events occurred in 1755, 1855, and 1946. Based on historical documents, we discuss two known damaging events in the sixteenth century: the 1524 Ardon and the 1584 Aigle earthquakes. For the 1524, a document describes damage in Ardon, Plan-Conthey, and Savièse, and a stone tablet at the new bell tower of the Ardon church confirms the reconstruction of the bell tower after the earthquake. Additionally, a significant construction activity in the Upper Valais churches during the second quarter of the sixteenth century is discussed that however cannot be clearly related to this event. The assessed moment magnitude Mw of the 1524 event is 5.8, with an error of about 0.5 units corresponding to one standard deviation. The epicenter is at 46.27 N, 7.27 E with a high uncertainty of about 50 km corresponding to one standard deviation. The assessed moment magnitude Mw of the 1584 main shock is 5.9, with an error of about 0.25 units corresponding to one standard deviation. The epicenter is at 46.33 N and 6.97 E with an uncertainty of about 25 km corresponding to one standard deviation. Exceptional movements in the Lake Geneva wreaked havoc along the shore of the Rhone delta. The large dimension of the induced damage can be explained by an expanded subaquatic slide with resultant tsunami and seiche in Lake Geneva. The strongest of the aftershocks occurred on March 14 with magnitude 5.4 and triggered a destructive landslide covering the villages Corbeyrier and Yvorne, VD.
[en] Complete text of publication follows. Possible pre-seismic variations in the geomagnetic total force field observed at a station that is approximately 70 km away from the epicenter of the 1995 Hyogo-ken Nanbu (Kobe) earthquake are discussed. The preliminary result obtained by using a simple difference method shows that there is a gradual decrease in values obtained three months before and a sudden increase in values obtained ten days before the earthquake. In order to determine whether these changes are tectonic signals, data are corrected by means of the regional geomagnetic field model constructed by using data from five reference magnetic observatories in Japan. On the basis of the analysis, it is clarified that the detected changes are local signals. Moreover, the application of the statistical model quantifies the sudden increase as 3.0 nT and the gradual decrease as approximately 3.0 nT; the latter value is considerably larger than the usual annual variation at the site.
[en] Complete text of publication follows. Using 1-second magnetometer data recorded 65 km from the epicenter, Hayakawa et al.  and Miyahara et al.  identify changes in ultra-low frequency, magnetic polarization (the ratio of vertical to horizontal field components) occurring prior to and possibly related to the 1993 Mw 7.7 Guam earthquake. We compare these same 1-second Guam data with similar 1-second data from the Kakioka observatory (KAK) in Japan, and the global, magnetic activity index Kp. In analyzing many months of magnetic-polarization data before and after the earthquake, we find 1) analysis problems with both the Hayakawa et al. and the Miyahara et al. results, 2) significant correlation between the Guam and KAK data, and (3) an absence of precursory signals after removing common disturbances using KAK as a reference. We conclude that the observed changes in polarization are part of normal global magnetic activity and are unrelated to the earthquake.
[en] On the basis of textual research on the historical earthquake data and the field investigation of 1219 A.D. Guyuan earthquake, we suggest that there is only one strong earthquake occurred in Guyuan area in 1219 A.D., instead of two or three strong earthquakes. We further suggest that the earthquake parameters recorded in the present earthquake catalogs are not definite and should be modified. The occurrence time of this earthquake should be about 11 am, August 7, 1219 A.D. and the heavily-damaged area of this earthquake, the VIII intensity area, should be located among the regions of Guyuan, Pingliang and Longde county cities. The epicenter area should be near Guyuan city. The magnitude of this earthquake is about 7 and it has intensity about larger than or equal to IX within the epicenter area. The major axis direction of the heavily-damaged area strikes in north-northwest that is approximately consistent with the strike of the Liupan Shan thrust fault zone. The new tectonic activity of the Liupan Shan thrust fault zone resulted in the M7 Guyuan earthquake in 1219 A.D.
[en] Properties of the Olami-Feder-Christensen (OFC) model of earthquakes are studied by numerical simulations. The previous study indicated that the model exhibited 'asperity'-like phenomena, i.e., the same region ruptures many times near periodically [T. Kotani et al., Phys. Rev. E 77, 010102(R) (2008)]. Such periodic or characteristic features apparently coexist with power-law-like critical features, e.g., the Gutenberg-Richter law observed in the size distribution. In order to clarify the origin and the nature of the asperity-like phenomena, we investigate here the properties of the OFC model with emphasis on its stress distribution. It is found that the asperity formation is accompanied by self-organization of the highly concentrated stress state. Such stress organization naturally provides the mechanism underlying our observation that a series of asperity events repeat with a common epicenter site and with a common period solely determined by the transmission parameter of the model. Asperity events tend to cluster both in time and in space.