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We present a catalog of accurate epicenter coordinates of earthquakes located in the Gulf of California (GoC) in the period 2002–2014 that permits us to analyze the seismotectonics and to estimate the depth of the seismogenic zone of this region. For the period April 2002 to December 2014 we use body-wave arrival times from regional stations of the Broadband Seismological Network of the GoC (RESBAN) operated by CICESE to improve hypocenter locations reported by global catalogs. For the northern region of the GoC (30°N–32°N) we added relocated events from the 2011-Hauksson-Yang-Shearer, Waveform Relocated Earthquake Catalog for Southern California (Hauksson et al., 2012; Lin et al., 2007). From October 2005 to October 2006 we incorporated hypcenters located by Sumy et al. (2013) in the southern GoC combining an array of ocean-bottom seismographs, of the SCOOBA experiment, with onshore stations of the NARS-Baja array. This well constrained catalog of seismicity highlights zones of active tectonics and seismic deformation within the North America-Pacific plate boundary. We estimate that the minimum magnitude of completeness of this catalog is Mc = 3.3 ± 0.1 and the b = 0.92 ± 0.04 value of the Gutenberg-Richter relation. We find that most earthquakes in the southern GoC are generated by transform faults and this region is more active than the central GoC region. However, the northern region, where most deformation is generated by oblique faults is as active as the southern region. We used the ISC catalog to evaluate the size distribution of seismicity of these regions, and the b value of the Gutenberg-Richter relation and found that b is slightly lower in the central GoC ( b = 0.86 ± 0.02) compared to the northern ( b = 1.14 ± 0.04) and the southern ( b = 1.11 ± 0.04) regions. We observed seismicity that occurs in the Stable Central Peninsular Province, despite the fact that significant active deformation has not been identified in this region. [ABSTRACT FROM AUTHOR]

I investigated postseismic velocity changes within focal area of the 2013 M 7.0 Lushan earthquake using coda-wave data of repeating small earthquakes. I employed template matching and grid search methods to identify well-defined repeating earthquakes in order to minimize artifacts induced by variations in source location. I identified a total of 3 isolated patches in a two-month period after the M 7.0 mainshock. I applied the coda wave interferometry technique to the waveform data of the identified repeating earthquakes to estimate velocity changes between the first and subsequent events in each cluster. Up to 0.1–0.2% velocity increase is observed from the S coda of repeating events occurred at regions surrounding the large coseismic slip area at seismogenic depths. My observations suggest that a large percent of velocity changes may occur at surface near the stations or shallow, however, healing along the propagation paths in the deep (~ 5–20 km) is likely have contributed to the amount of velocity changes observed after the Lushan earthquake. [ABSTRACT FROM AUTHOR]

Seismical parameters of five seismogenic zonings for the Iberian Peninsula have been determined in this work. For that purpose, this research has two key goals. The first is to generate a seismic catalog. The second to calculate the seismical parameters of all the zones of the seismogenic zonings selected. The first key goal has been the creation of a catalog of earthquakes for the Iberian Peninsula and adjacent areas. First, the National Geographic Institute of Spain's catalog has been completed and reviewed with the information from other catalog reviews and specific studies. Second, all magnitude calculations have been homogenized. Third, all dependent data have been eliminated through declustering. Finally, the year of completeness for each magnitude has been considered. The Quaternary active faults database of Iberia has also been used as input data. All of this information has been integrated into a geographic information system. The second key aim is the calculation of the seismical parameters. The first parameter obtained has been the b -value. A method which considers different years of completeness in accordance with the magnitude has been used. Also, the annual rate of earthquakes per square kilometer has been calculated. Moreover, the maximum magnitude known that Quaternary active faults might generate and maximum magnitude recorded in the catalog have been determined. Finally, based solely on the statistical parameters obtained, a critical discussion of the seismogenic zonings of the Iberian Peninsula has been conducted. The results show that some zonings possess insufficient data for a proper calculation of the seismic parameters, from a statistical point of view. [ABSTRACT FROM AUTHOR]

We conducted a systematic detection of micro-seismicity in Southern Tibet 1.6 days before and 4.4 days after the 2015 Mw 7.8 Gorkha, Nepal earthquake. Our study employs 368 template events listed in the China Earthquake Networks Center (CENC) catalog. With the waveform-based matched filter technique, we detected five times more earthquakes than listed in the CENC catalog during our study period. The seismicity in Southern Tibet shows a significant increase immediately following the Gorkha, Nepal earthquake, including two normal-faulting events (the Mw 5.8 Tingri and Mw 5.3 Nyalam earthquakes) about 3 and 11 h after the mainshock, respectively. Although the static stress changes ΔCFS showed a slightly better correlation with the seismicity rate changes than the peak dynamic stress changes ΔCFS( t ), the absolute value of the static stress change at the epicenter region of the Mw 5.8 Tingri earthquake is ~ 10 kPa, roughly two orders smaller than the peak dynamic stress change of 2.2 MPa. Although we are unable to identify the primary triggering mechanism, it is evident that the 2015 Nepal earthquake triggered widespread seismicity in Southern Tibet. Our results highlight the potential increase of seismic hazard in Southern Tibet due to the occurrence of major thrust earthquakes along the Himalaya frontal thrust faults. [ABSTRACT FROM AUTHOR]

In this study, the seismicity that occurred in Aswan region from 1982 to 2015 is investigated using robust statistical methodologies. The completeness magnitude, estimated by using two different methods (MAXC and GFT) is 2.5 for the whole catalog with b ~ 1.07. By using the expectation maximization algorithm, two depth classes of events were identified with a threshold at about 12 km. The events deeper and shallower than the threshold could be likely generated by the same mechanism: the loading/unloading operation of the Lake Nasser reservoir. We suggest that the shallow seismicity occurs on shallow small fractures in correspondence of the intersection of N-S faults with E-W faults, which may form a minor pull-apart basin. The deep events mainly occur along the right-lateral, strike-slip, E–W Kalabsha fault and the seismicity is characterized by mainshock-aftershocks sequences that mask the annual periodicity if not properly aftershock-depleted. Indeed, before applying the declustering on the seismic catalog, the analysis of the time-clustering properties of the shallow earthquakes reveals already the presence of annual modulation that is not evident in the time dynamics of the deep earthquakes. Furthermore, the shallow events are featured by the Allan Factor scaling exponent (measuring the strength of the time-clustering in an earthquake sequence) lower than that of the deep events, indicating a tendency of the time dynamics of the shallow earthquakes to behave more regularly than the deep ones. The detrended fluctuation analysis of the magnitude series suggests that the earthquake series are weakly persistent, characterized by the tendency of events of similar value of magnitude to follow each other. [ABSTRACT FROM AUTHOR]

We present a detailed analysis of the seismic activity in the central Apennines based on a high quality seismogram data set collected from two temporary and three permanent networks. This integrated network recorded, between January 2009 and December 2013, a total of 7011 local earthquakes (6270 selected for this study), with local magnitudes M L ranging from 0.4 to 4.7. Hypocentres were located by using a reference 1D crustal velocity model determined with a genetic algorithm. The majority of the hypocenters are located beneath the axis of the Apenninic belt, while the rest are found along the peri-Tyrrhenian margin. Hypocentral depth distribution extends to a depth of 31 km with a pronounced peak between 8 and 12 km. Both low-to-moderate magnitude seismic sequences and diffuse swarm-like seismicity was observed. There were two major seismic swarms and a seismic sequence, which included the Marsica-Sora M L 4.7 main shock. A total of 468 fault plane solutions were derived from P -wave polarities. This new data set more than quadruples the number of focal mechanisms that was previously available for regional stress field analysis in the study region. The majority of the fault plane solutions in the central Apennines show predominantly normal fault movements, with T-axis trends oriented NE-SW. Focal mechanisms calculated in this study confirm that this area is in extension. For the seismic swarms-sequence in the Marsica-Sora area we also derived the azimuth and plunge of the principal stress axes by inverting fault plane solutions. We find a few right-lateral strike-slip focal mechanisms that possibly identify the prolongation of the strike-slip kinematics in the Gargano-Apulia foreland to the west, and mark the passage to the NW-SE striking normal faults of the inner Apenninic belt. The seismicity and stress distribution we observe might be consistent with a fragmented tectonic scenario in which faults with small dimensions release seismic energy in a diffused way. [ABSTRACT FROM AUTHOR]

Constraining the maximum likely magnitude of future earthquakes on continental transform faults has fundamental consequences for the expected seismic hazard. Since the recurrence time for those earthquakes is typically longer than a century, such estimates rely primarily on well-documented historical earthquake catalogs, when available. Here we discuss the maximum observed earthquake magnitudes along different sections of the North Anatolian Fault Zone (NAFZ) in relation to the age of the fault activity, cumulative offset, slip rate and maximum length of coherent fault segments. The findings are based on a newly compiled catalog of historical earthquakes in the region, using the extensive literary sources that exist owing to the long civilization record. We find that the largest M7.8–8.0 earthquakes are exclusively observed along the older eastern part of the NAFZ that also has longer coherent fault segments. In contrast, the maximum observed events on the younger western part where the fault branches into two or more strands are smaller. No first-order relations between maximum magnitudes and fault offset or slip rates are found. The results suggest that the maximum expected earthquake magnitude in the densely populated Marmara–Istanbul region would probably not exceed M7.5. The findings are consistent with available knowledge for the San Andreas Fault and Dead Sea Transform, and can help in estimating hazard potential associated with different sections of large transform faults. [ABSTRACT FROM AUTHOR]

Abstract: During one month, in October and November 2010, the region of Sampeyre (Western Alps, Italy) was struck by a seismic activity of several hundred events. The location of 287 events recorded at least by three stations showed a diffuse swarm ranging between 8 and 13km depth. The number of earthquakes in the database was increased thanks to a detailed analysis of the continued recordings of the nearest station (DOI) which allowed identifying 2612 earthquakes. The temporal distribution of the seismicity is characterized by the alternation of active and quiescent periods. Moment magnitude was computed for 730 events by a P wave spectral analysis of the DOI station data. The estimated magnitudes range between 0.7 and 3.15. The b-value of the cumulated frequency–magnitude distribution is around 1.4. Spatio-temporal analysis of the located earthquakes highlighted an overall northward migration of the seismicity. From spatio-temporal criteria, the seismicity was divided in three clusters. Each cluster is characterized by its own focal mechanism family. The stress tensor determined from the focal mechanisms indicates probable stress heterogeneities at small spatial scale. The observed migration of the seismicity could be compatible with earthquake triggering by fluid diffusion processes. [Copyright &y& Elsevier]

Crustal deformation due to the 2016 earthquake sequence in Kumamoto, Japan, that culminated in a preceding earthquake of magnitude M 6.5 and a subsequent M 7.3 earthquake 28 h later, caused stress perturbation on and around the causative Futagawa-Hinagu fault zone. Monitoring changes in seismicity pattern along this zone plays a role in understanding the process before and after major earthquakes. For this purpose, stress-dependent laws in statistical seismology can be used: the Gutenberg-Richter frequency-size law and the Omori-Utsu aftershock-decay law. We review the results obtained by using these laws in previous studies to show a zone of high stress near the eventual epicenters of the M 6.5 and M 7.3 earthquakes before the start of the Kumamoto sequence, and after it, showing a decreasing trend in stress along the Futagawa-Hinagu fault zone. Detailed analysis suggests aseismic slips along the causative fault zone. The aseismic preslip locally reduced stress just prior to the M 7.3 earthquake near its epicenter. Recently, a system was proposed by Gulia and Wiemer (2019) that utilizes the Gutenberg-Richter frequency-size law to judge, immediately after a large earthquake, whether it was the mainshock or a foreshock to a future event. Based on the reviewed results and our new results, further research that takes into account the spatial variation of frequency-size distribution, allowing the exploration of the possibility of a local preslip of a future nearby earthquake, is needed to improve this system. [Display omitted] • Changes in seismicity and stress distribution due to the 2016 Kumamoto earthquakes. • Stress field revealed aseismic pre- and after-slow slips along the causative faults. • System to discriminate foreshocks and aftershocks was tested for the Kumamoto case. • Test showed that seismicity before the largest event was regarded as aftershocks. • Aseismic slips and changes in stress are keys to modify the discrimination system. [ABSTRACT FROM AUTHOR]

Abstract: We obtained the coseismic deformation field of the Ms7.1 earthquake in Yushu, Qinghai, China on 14 April 2010 using L band and C band SAR images. The results show that the deformation fields derived from L and C bands separately are consistent in general. They are all characterized by concentric elliptic interference fringes surrounding a NW trending fault with two local intensively deformed regions. Meanwhile they have small differences in area coverage of the deformation field, magnitude of LOS displacements and other details of deformation nearby the fault. The deformation from C band and L band covers 89∗59km square and 77∗43km square, with maximum displacements of about 45cm and 65cm in the radar line of sight, respectively. Using these two kinds of InSAR measurements separately and jointly, we constructed a three-segment fault model and inverted the coseismic fault slip of the Yushu event. The inversion results show that the slip distributions constrained by the two kinds of inSAR data are in agreement on the whole. They all indicate two concentration regions of slip distribution, one is located near the Jiegu town on the southeastern segment of the Yushu fault with a large area and the maximum slip of 2.4m, and the other is at the epicenter on the northwestern segment of the fault with a relatively small area. There are also discrepancies between the two kinds of slip distribution models. In general, the scale, magnitude, and depth of slip distribution constrained by C band ASAR data are larger than that by L band PALSAR data. The slip distribution from a joint inversion of the two kinds of SAR data is considered to be the most robust model compared to the results of that constrained by L band SAR data or C band SAR data alone. [Copyright &y& Elsevier]

Abstract: Occurring in the southwest of Western Australia, the 1968 Meckering earthquake (M S 6.8) resulted in the formation of an extensive surface rupture complex comprising faults with a range of orientations and reverse and dextral lateral offsets. Modeling of the seismological characteristics of the source showed that reverse failure occurred on a north–south striking, east-dipping surface, but how this is related to the local Precambrian bedrock geology is not clear. Interpretation of new aeromagnetic data has allowed concealed bedrock lithology and structure to be mapped in previously unachievable detail. These data show that the surface faulting correlates closely with linear magnetic anomalies, interpreted as dykes/faults and lithological contacts. The complicated pattern of surface faulting contrasts with the more simple seismological fault model, but can be explained in terms of the reactivation of northeasterly (dykes and faults) and northwesterly (stratigraphic) trending features in a stress regime with an east–west oriented maximum principal stress. Space problems created where these two trends converge led to the creation/reactivation of a linking north–south trending thrust fault which accommodated the greatest displacements recorded for the 1968 event. The district scale distribution of epicentres in the 3 years encompassing the Meckering event shows the same northeasterly and northwesterly trends as seen in the aeromagnetic data. The implied basement features controlling the seismicity will be prone to strike–slip failure in the regional, east–west oriented stress field. It is speculated that smaller events in the Meckering area will tend to be strike–slip and these account for most of the strain. Larger events, all known examples of which involve predominantly thrusting, are caused by stress build up where strike–slip faults with the two orthogonal trends intersect. This hypothesis provides an explanation for the lack of topography in the region, which is incompatible with the high level of seismic activity and a predominance of thrust faulting. [Copyright &y& Elsevier]

Abstract: We have analysed three recent earthquake sequences in the northern part of the Taupo Volcanic Zone. A 1998 sequence at Haroharo with a largest event of M L 4.8, and a 2004 sequence near Lake Rotoehu (largest event M L 5.4), had normal b-values, and displayed an aftershock decay pattern, with most of the activity within the first few days. In contrast, a 2005 sequence a few tens of kilometres away at Matata (largest event M L 4.1), had very different characteristics, with a slow development and decay, no tendency for enhanced seismicity after the larger events, and a very high b-value. The focal mechanisms of the Rotoehu and Matata events are normal, and have stress patterns consistent with the geodetically observed extension of the Taupo Volcanic Zone in a northwest–southeast direction. The extensive recent volcanism in the Okataina Volcanic Centre does not seem to have affected the stress pattern in this area. The Rotoehu sequence showed a strong resemblance, particularly in the time distribution of events, to the well-known swarm activity in the Vogtland region on the German/Czech border, in which larger events were followed by a burst of seismicity, as in a normal aftershock sequence. Some of the arguments that have been advanced to explain the Vogtland swarm as seismicity induced by fluid injection apply to Rotoehu, but there is no direct evidence of fluid involvement. The Matata sequence appears to have a continuing trigger mechanism, either a slow injection of fluid, or a slow slip event, in an environment in which opening pore spaces prevent high overpressures developing. The Matata sequence occurred close to the area of the 1987 M L 6.3 Edgecumbe Earthquake, so exhibiting two extremes of seismic temporal pattern, namely mainshock–aftershock and a swarm with many events of similar magnitude, within a small area. [Copyright &y& Elsevier]

Abstract: In the Kanto region, there have been reports of decreasing b-values prior to earthquakes (M ≥5.5). The change of b-values is defined as the difference between the long- and short-term average earthquake magnitudes. A hazard function for moderately large earthquakes has also been proposed. This model was based on earthquakes that occurred between 1982 and 1999, and its effectiveness is measured retrospectively. In order to evaluate the effectiveness of the model through the use of independent data, the verification test is based on earthquakes observed after January 2000. Through the end of 2004, the only event where there was a decrease in mean event size was observed on June 3, 2000. This decrease resulted in a log-likelihood for the proposed model 1.3 units larger than that of the Poisson model, supporting the validity of the proposed model. Without accumulating further examples, we attempted to improve the verification test by expanding the study volume and by lowering the target cutoff magnitude in order to overcome the small sample size. When two other targets from the expanded volume were added, the difference in the log-likelihood (ΔlnL) increased to 3.6. In this case, the information rate per event was about 1.2, larger than that of the model period. Lowering the cutoff magnitude increased ΔlnL to 2.5. These extended tests led to higher confidence in the model with the larger ΔlnL value than did the primary test. From the viewpoint of the per-event information rate, each case involving targets with a magnitude 5.5 and larger resulted in better performance than in the model period. [Copyright &y& Elsevier]

Abstract: The Elat fault (a segment of the Dead Sea Transform) runs along the southern Arava valley (part of the Dead Sea Rift, Israel) forming a complex fault zone that displays a time-dependent seismic behaviour. Paleoseismic evidence shows that this fault zone has generated at least 15 earthquakes of magnitude larger than M 6 during the late Pleistocene and the Holocene. However, at present the Elat fault is one of the quietest segments of the Dead Sea Transform, lacking even microsesimicity. The last event detected in the southern Arava valley occurred in the Avrona playa and was strong enough to have deformed the playa and to change it from a closed basin with internal drainage into an open basin draining to the south. Paleoseismological, geophysical and archaeological evidences indicate that this event was the historical devastating earthquake, which occurred in 1068 AD in the eastern Mediterranean region. According to the present study this event was strong enough to rupture the surface, reactivate at least two fault branches of the Elat fault and vertically displace the surface and an early Islamic irrigation system by at least 1 m. In addition, the playa area was uplifted between 2.5 and 3 m along the eastern part of the Elat fault shear zone. Such values are compatible with an earthquake magnitude ranging between M 6.6 and 7. Since the average recurrence interval of strong earthquakes during the Holocene along the Elat fault is about 1.2±0.3 ky and the last earthquake occurred more about 1000 years ago, the possibility of a very strong earthquake in this area in the future should be seriously considered in assessing seismic hazards. [Copyright &y& Elsevier]

We test the sensitivity of seismic hazard to three fault source models for the northwestern portion of Gujarat, India. The models incorporate different characteristic earthquake magnitudes on three faults with individual recurrence intervals of either 800 or 1600 years. These recurrence intervals imply that large earthquakes occur on one of these faults every 266–533 years, similar to the rate of historic large earthquakes in this region during the past two centuries and for earthquakes in intraplate environments like the New Madrid region in the central United States. If one assumes a recurrence interval of 800 years for large earthquakes on each of three local faults, the peak ground accelerations (PGA; horizontal) and 1-Hz spectral acceleration ground motions (5% damping) are greater than 1 g over a broad region for a 2% probability of exceedance in 50 years'' hazard level. These probabilistic PGAs at this hazard level are similar to median deterministic ground motions. The PGAs for 10% in 50 years'' hazard level are considerably lower, generally ranging between 0.2 g and 0.7 g across northwestern Gujarat. Ground motions calculated from our models that consider fault interevent times of 800 years are considerably higher than other published models even though they imply similar recurrence intervals. These higher ground motions are mainly caused by the application of intraplate attenuation relations, which account for less severe attenuation of seismic waves when compared to the crustal interplate relations used in these previous studies. For sites in Bhuj and Ahmedabad, magnitude (M) 7 3/4 earthquakes contribute most to the PGA and the 0.2- and 1-s spectral acceleration ground motion maps at the two considered hazard levels. [Copyright &y& Elsevier]