Journal of Seismology最新文献

The significant Mw 6.1 Kopili Fault earthquake that struck on April 28, 2021, profoundly impacted causing substantial structural damage, ground cracks, liquefaction, provides an important instance to examine seismic processes in the Kopili Fault region. Considering an integrated approach, the study aims to quantify ground deformation, hydrological changes, seismicity and strong ground motion parameters, to evaluate its implications for regional seismic hazard. DInSAR analysis indicates no significant coseismic ground deformation in the epicentral region, with a mean deformation of about -0.71 (pm) 9.71mm while NDWI analysis indicate increase in humid surface from 0.41% to 0.62% in Missamari area characterized by liquefaction, suggesting the development of new pits signifying subsidence. Intense seismic activity, observed from database of 6336 events during 1964 to 2022, highlight clusters of aftershocks, suggesting continued stress transfer and fault reactivation mainly at depth of 10-30km. Evidently, the event is characterised by intersection of Kopili Fault to the HFT in lower Himalaya imparting stress to the rupture area of the fault. Stress tensor inversion of fault plane solutions indicates NNE directed principal stress, reflecting the prevailing stress conditions of the Kopili valley, aligned with regional pattern. Notably, accelerograms recorded at five SMA stations showed high shaking in the epicentral region, by strong site-to-site variability influenced by local geology and basin effects identifying stiff rock at Agia and Tura; and softer rock at Jorhat, Guwahati and Golaghat. Detail analysis of ground motion parameters portray peak ground acceleration during the main event is highest at Guwahati (0.05g), indicating MMI IV shaking intensity. The parameters investigated under this study contribute to a better understanding of the regional tectonics and fault behaviour, providing valuable insights into the consequences of the 2021 earthquake and its implications for future events.

Seismic anisotropy is a robust mechanism to infer the strength and direction of deformation in the crust, lithosphere, and sub-lithospheric mantle. This study presents new shear wave splitting (SWS) measurements from the Sikkim Himalaya region utilizing the core refracted (SKS/SKKS/PKS) and crustal (direct-S) seismic phases to understand the mantle and crustal-scale deformation patterns, respectively. Significant time delays ((delta t)) and consistent NW-SE oriented fast polarization directions ((phi )) at all seismic station locations emphasize the dominance of Indo-Eurasian collisional tectonics in governing the deformation patterns beneath Sikkim. The boundary conditions implied by collisional tectonics require deformation with a large amount of shortening of the lithosphere beneath this Sikkim region. A similar crustal deformation pattern (NE-SW) led by the alignment of maximum shear stress is observed throughout this Himalayan region, suggesting that the huge collisional tectonic force influences the coupled crust-mantle dynamics. The deformation in the proximity of regional crustal-scale structures is controlled by the shape-preferred orientation of cracks/voids. Throughout the Sikkim Himalaya, the majority of crustal anisotropy parameters seem to be dominated by the maximum shear (arc-parallel) of convergence tectonics.

Strong seismic activity in southwestern China poses a serious threat to public safety. Though ground motion models (GMMs) are essential for ensuring that structures have sufficient seismic capacities, only the horizontal GMMs have been extensively obtained for southwestern China; few vertical GMMs have been developed. Owing to the lack of near-field records for large earthquakes in this region, this study established a model for predicting the vertical-to-horizontal spectral acceleration (V/H) ratios using an empirical reference approach. The results indicate that the predicted V/H ratios for southwestern China increased with increasing earthquake magnitude, particularly for short-period motions. The short-period V/H ratios decreased with increasing source distance, whereas the trend was the opposite for the long-period V/H ratios. Furthermore, the short-period V/H ratios decreased, then remained nearly constant with increasing V_S30 (where V_S30 is the average shear-wave velocity to 30 m depth), whereas the long-period V/H ratios consistently increased. Additionally, the results indicate that the peak V/H ratio in soil site in near-field was larger than 2/3 with a maximum value of 1.68. Finally, the residuals of the adjusted model showed no significant bias regarding the predictor variables, and the V/H ratio curve predicted by the adjusted model crossed through the center of the recorded V/H ratio data. Thus, the adjusted model derived in this study showed good agreement with observed data in southwestern China and can be used as a reference for seismic design in this region.

The occurrence of clustered events has a certain impact on the understanding of seismic activity patterns. Moreover, most current declustering algorithms rely on the setting of thresholds. The settings of magnitude and clustering thresholds are two key factors affecting the declustering effect of the nearest-neighbor algorithm. Taking North China as a case study, we conducted a systematic test on the threshold parameters and analyzed the declustering effects under different threshold conditions and their impacts on seismic activity parameters. The research shows that as the magnitude threshold increases, the declustering rate decreases. The proportion of low-magnitude events as clustered events is relatively high, while high-magnitude events are mostly background events. The declustered b-value increases with the increase of the magnitude threshold. There are certain differences in the Poisson distribution characteristics under different thresholds. The clustering threshold is inversely proportional to the declustering rate. As the clustering threshold increases, the number of removed earthquakes decreases, resulting in an enhancement of the overall seismic activity, but it does not significantly change the relative spatial intensity. The clustering threshold is positively correlated with seismicity parameters a-value and b-value. The spatial variation of the b-value is relatively gentle. The phenomenon of low b-values appears in areas with complex seismic faults such as the Zhangjiakou-Bohai tectonic belt, which are still potential hazardous areas that need to be focused on in the future. An increase in the clustering threshold makes the spatial description of the b-value more detailed. There are certain commonalities in the low b-value areas, which also reflects that different clustering thresholds do not change the crustal stress state. Analyzing the influence of different threshold settings on the declustering rate and seismic activity parameters plays an important reference role in accurately grasping seismic activity characteristics and improving the accuracy and reliability of probabilistic seismic hazard analysis.

This study investigates Montenegro's seismic characteristics and tectonic stress distribution using the Gutenberg-Richter Law, stress inversion, and focal mechanism analysis. A dataset of 7727 earthquakes (0.8 ≤ Mw ≤ 7.1) is analyzed to evaluate seismicity patterns. A comprehensive statistical assessment includes cumulative earthquake numbers, cumulative seismic moment release, and magnitude–depth distributions. The spatial variation of seismicity is mapped. Additionally, b–value mapping is performed to identify regions of varying stress accumulation and seismic hazard potential. Focal mechanism solutions of 33 earthquakes (3.2 ≤ Mw ≤ 7.1) are analyzed to determine faulting styles and tectonic deformation patterns. Stress inversion techniques are applied to infer the orientation of principal stress axes and understand regional tectonic forces. These analyses provide a detailed characterization of Montenegro's seismotectonic regime, contributing to a better understanding of earthquake generation mechanisms and their implications for seismic hazard assessment. The findings of this study emphasize the seismic vulnerability of Montenegro, particularly in its southern and coastal regions. Considering the observed stress accumulation and historical seismicity, future large earthquakes are likely to occur. Strengthening seismic monitoring networks, updating building codes, and enhancing public awareness programs are crucial to improving regional resilience against future seismic events. To the best of our knowledge, this is the first study to comprehensively analyze Montenegro's seismicity using integrated b–value mapping, stress tensor inversion, and focal mechanism classification.

The Valle de la Trinidad region in northern Baja California is situated within a seismically active zone at the boundary between the Pacific and North American plates, characterized by complex fault interactions and significant crustal deformation. We investigate the seismicity of this region between 2010 and 2024 to better characterize active structures and earthquake interactions. Using waveform-based double-difference relocation, we refine the hypocentral locations of 4010 earthquakes with magnitudes ranging from ML 0.3 to 5.1 recorded by the Seismic Network of Northwest Mexico (RESNOM), significantly reducing epicentral and depth uncertainties. The relocated seismicity reveals clear alignment with the San Miguel fault and a previously unmapped intersecting structure, indicating that both faults are actively accommodating regional strain. Moment tensor inversions of the events with ML (ge ) 4 show consistent right-lateral strike-slip mechanisms, with nodal planes aligned with both structures, although ambiguity remains regarding the exact fault that ruptured. The August 17, 2020 seismic sequence, initiated by an ML 4.7 foreshock and an ML 5.1 mainshock, demonstrates that triggering across intersecting faults may control rupture evolution. Temporal changes in focal mechanisms, from strike-slip to normal faulting, suggest stress field variations during the sequence. These results highlight the seismotectonic complexity of fault intersections in the Peninsular Ranges and emphasize the need to reassess seismic hazard models to incorporate the role of previously unmapped structures.

Macroseismic surveys are of great interest to both the scientific community and the authorities.The aim of the MACROSISDATA project is to safeguard, disseminate, and promote through an online database the macroseismic survey documents collected by the French Central Seismological Bureau between 1921 and 1996. During this period, a total of 1428 earthquakes were surveyed to estimate macroseismic intensities (severity of ground shaking) by sending paper forms to the municipal authorities. This unique collection of forms, letters, maps, newspaper articles, and macroseismic reports amounts to 29 linear meters of archival paper documents. The 5-year MACROSISDATA project (2020–2025) consisted of 9 stages, from inventorying archival documents to online publication of digitized documents on a national website. The last stage will be implemented at the end of 2025. The stages were developed with the support of the archives department of the University of Strasbourg, comply with French archive management rules, and adopt a strategy that makes the data easily findable, accessible, interoperable and reusable (FAIR). In this article, we describe each stage in detail.

The Doruneh Fault System, Iran’s second-largest fault zone, generates infrequent but large-magnitude earthquakes with long recurrence intervals. Limited historical data from this sparsely populated desert region challenge reliable seismic hazard assessments. We address this gap by developing a 50,000-year synthetic seismicity model for the Doruneh Fault System using Virtual Quake, independent of observed catalogs. The model produces seismicity rates consistent with available data and enables the calculation of time-dependent conditional probabilities and expected waiting times (EWTs) for earthquakes of M6 + and above. Given the fault’s extensive length and proximity to urban and industrial centers, these findings enhance seismic hazard evaluations for the region. Our study demonstrates the value of synthetic seismicity models in data-scarce regions, providing critical insights for earthquake risk mitigation.