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SEISMOGENIC FAULT AND COSEISMIC SURFACE DEFORMATION OF THE DINGRI MS6.8 EARTHQUAKE IN XIZANG, CHINA SHI Feng, LIANG Ming-jian, LUO Quan-xing, QIAO Jun-xiang, ZHANG Da, WANG Xin, YI Wen-xing, ZHANG Jia-wei, ZHANG Ying-feng, ZHANG Hui-ping, LI Tao, LI An SEISMOLOGY AND GEOLOGY    2025, 47 (1): 1-15.   DOI: 10.3969/j.issn.0253-4967.2025.01.001 Abstract （2477）   HTML （80）    PDF（pc） （13725KB）（1130）       Knowledge map    Save At 09:05 am on January 7, 2025, a MS6.8 earthquake occurred in the Dingri, Xizang, China. The earthquake caused serious casualties and property losses. Research on the seismogenic structure and characteristics of earthquake surface rupture in this earthquake is beneficial to understanding the rupture behavior and dynamic mechanism of normal-fault earthquakes. Meanwhile, it provides a basis for predicting the future strong earthquake trend of the southern Xizang rift fault system. Its epicenter is located at 87.45°E, 28.50°N, 13km depth, the China Earthquake Networks Center measures. In order to constrain the seismogenic fault and characterize the co-seismic surface ruptures of this earthquake, field investigations were conducted immediately after the earthquake, combined with analyses of the focal parameters, aftershock distribution, and InSAR inversion of this earthquake. This preliminary study finds that the seismogenic fault of the Dingri MS6.8 earthquake is the Dengmocuo fault, which is an active ~60km long, NS-NE-striking and normal fault. The total length of the co-seismic surface ruptures is approximately 25km, located on the north segment of the Dengmocuo fault. Meanwhile, a dense deformation zone of ground fracture with a length of ~10km is generated on the east side of Dengmocuo Lake along the contour line of the lake shore. The earthquake also induced a large number of liquefaction structures and tensional fractures in valleys and basins. Based on along-strike discontinuity due to the development of step-overs, the coseismic surface rupture zone can be subdivided into three segments: the Gurong-Qiangga, Nixiacuo, and Yangmudingcuo segments. The surface ruptures are relatively continuous and prominent along the Nixiacuo segments. Comparatively, co-seismic surface ruptures of Gurong-Qiangga and Yangmudingcuo segments are discontinuous. The maximum of coseismic vertical displacement is roughly determined to be 2.5—3.0m based on the scarps. The width of the surface rupture zone of the Dingri earthquake can reach up to 450m in some areas. The location of surface rupture zones is not limited to fault scarps and hanging walls. There are also a large number of secondary scarps and cracks distributed in the footwall. Many cracks are distributed in an en echelon or grid pattern. Compared to the continuous surface rupture caused by strike-slip-type earthquakes in recent years, the surface rupture of the Dingri earthquake is very discontinuous, and there is an obvious difference in displacement between each segment of the surface rupture. Preliminary speculation suggests that it may be related to the characteristics of the fault movement. Unlike strike-slip faults where the dislocation direction is parallel to the strike, the dislocation direction of normal faults is perpendicular to the strike. In addition, the observed length of surface rupture and maximum displacement of the Dingri earthquake are basically consistent with the results calculated by empirical formulations. Table and Figures | Reference | Related Articles | Metrics

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SURFACE DEFORMATION CHARACTERISTICS AND CAUSES OF THE DENGMECUO SEGMENT IN THE XIZANG DINGRI MS6.8 EARTHQUAKE LIANG Ming-jian, DONG Yun-xi, ZUO Hong, DAI You-lin, XIAO Ben-fu, LIAO Cheng, TAN Ling, WANG Yu-wei, LI Xiang, TANG Cai-cheng, ZHANG Wei, ZHANG Hui-ping, MENG Ling-yuan, SU Jin-rong, WU Wei-wei, LI Chuan-you, YAN Mei SEISMOLOGY AND GEOLOGY    2025, 47 (1): 80-89.   DOI: 10.3969/j.issn.0253-4967.2025.01.006 Abstract （1317）   HTML （28）    PDF（pc） （5804KB）（304）       Knowledge map    Save On January 7, 2025, an MS6.8 earthquake struck Dingri, Xizang, China. According to the focal mechanism solution provided by the USGS, this event was characterized as a normal faulting earthquake. The earthquake occurred in the southern segment of the Shenzha-Dingjie Rift system, which is located on the Qinghai-Tibet Plateau. This rift system is one of the seven major rift systems in the southern part of the Tibetan plateau and is a significant controlling structure for shallow-source seismic activity within the region. Moderate to major earthquakes in the study area are primarily distributed along these rift systems. Notably, the Yadong-Gulu Rift system experienced an M8.0 earthquake in 1411 near the southern part of Dangxiong. The seismogenic fault of the earthquake is the Dengmecuo fault, which produced a 26-km-long surface rupture and deformation zone. The Dengmecuo fault is a branch of the southern segment of the Shenzha-Dingjie fault zone and is a Holocene active fault that controls the eastern boundary of the Dengmecuo Basin. The characteristics of the surface deformation zone in this earthquake differ between its northern and southern segments. The northern segment's surface rupture is primarily characterized by normal faulting, with a vertical co-seismic displacement of 2-3 meters. In contrast, the southern segment(the Dengmecuo segment)is mainly distributed on the eastern side of Dengmecuo Lake, with a width exceeding a hundred meters. The deformation characteristics of this segment are complex, exhibiting both extensional and compressional deformations. The extensional deformation zones in the southern segment, which align with the NNE-trending fault scarp, likely represent the tectonically seismogenic surface rupture zone of this earthquake. The compressive deformation zones, however, are believed to have formed as a result of the extensional deformation during the earthquake. These zones are influenced by seismic motion, local terrain, sedimentary characteristics, and climatic conditions and are not directly related to the fault's activity during the earthquake. The differences in the characteristics of the northern and southern segments of the surface deformation zone highlight the complexity of the geometric structure and motion properties of the Dengmecuo fault. Moreover, the main surface deformation zone in the southern section does not align with the surface traces of the Dengmecuo fault, suggesting that the fault may be gradually developing inward into the basin. Table and Figures | Reference | Related Articles | Metrics

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ANALYSIS OF BUILDING DAMAGE AND CASUALTIES OF THE 2025 DINGRI MS6.8 EARTHQUAKE IN XIZANG BASED ON FIELD INVESTIGATION WEI Ben-yong, ZHANG Yu-man, SHI Feng, QIAO Jun-xiang, WANG Xin, ZHANG Da SEISMOLOGY AND GEOLOGY    2025, 47 (1): 64-79.   DOI: 10.3969/j.issn.0253-4967.2025.01.005 Abstract （1011）   HTML （20）    PDF（pc） （10539KB）（331）       Knowledge map    Save On January 7, 2025, at 9:05 AM, a magnitude 6.8 earthquake struck Dingri County, Shigatse City, located in the southern part of the Xizang Autonomous Region(28.50°N, 87.45°E), with a focal depth of 10 kilometers. By 7:00 PM on January 9, the earthquake had resulted in 126 fatalities and 188 injuries. A total of 27, 248 buildings were damaged, including 3, 612 collapsed structures. Timely understanding and analysis of the earthquake's damage characteristics and the causes of casualties can provide valuable references for subsequent disaster loss assessments and recovery planning. Based on field investigations, this study provides a comprehensive overview of the earthquake damage, covering four main aspects: seismic characteristics and affected areas, seismogenic fault and aftershock distribution, building damage and influencing factors, and the distribution and causes of casualties. The study also analyzes in detail the reasons for the severe casualties in this earthquake. The epicenter of the Dingri earthquake is located within the Lhasa block of the Tibetan Plateau. The earthquake was triggered by the Dengmecuo fault, a normal fault characterized by crustal extension due to fault slip. The maximum intensity of this earthquake reached IX degree, and the major axis of the isoseismal line runs nearly north-south, with a length of 191 kilometers and a short axis of 152 kilometers. The area affected by intensity VI or higher is approximately 23986 square kilometers, covering six counties and 45 towns(or streets)in Shigatse City, Xizang Autonomous Region. The earthquake caused a surface rupture of approximately 26 kilometers, with a maximum vertical displacement of about 3 meters. Field investigations revealed that the building structures in Dingri County mainly consist of frame, masonry, and traditional civil structures. Among these, traditional civil structures sustained the most severe damage. In extremely and severely affected areas, the majority of civil-structure buildings were either destroyed or severely damaged, with complete or partial collapses occurring. The main factors contributing to the severe damage to civil-structure buildings include the lack of seismic resistance measures, poor construction techniques, and inadequate shear resistance and bond strength of construction materials. The majority of casualties were concentrated in Changsuo, Cuoguo, and Quluo towns, near the epicenter. Changsuo town suffered the most severe damage, with casualties accounting for 74.60% of the total fatalities. The high casualty rate can be attributed to the strong destructive power of the earthquake, the proximity of villages to the fault lines, low seismic performance of buildings, high population density, and adverse environmental conditions such as low temperatures and oxygen deficiency. Based on the analysis of the causes of casualties and field investigations, this study proposes targeted countermeasures and suggestions to mitigate earthquake disaster risks and minimize casualties in Xizang. These measures include enhancing active fault detection, improving earthquake early warning capabilities, reducing seismic damage risks to traditional residential buildings, strengthening emergency response measures, mitigating the risk of secondary earthquake disasters, and increasing public awareness of earthquake risks. These recommendations aim to enhance the region's earthquake prevention and mitigation capabilities and provide guidance for post-disaster recovery and reconstruction. Table and Figures | Reference | Related Articles | Metrics

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INVESTIGATION OF THE SEISMOGENIC STRUCTURE OF THE 2025 DINGRI MS6.8 EARTHQUAKE IN XIZANG BASED ON THE TECTONIC STRESS FIELD PERSPECTIVE SHENG Shu-zhong, WANG Qian-ru, LI Zhen-yue, LI Hong-xing, ZHANG Xiao-juan, GE Kun-peng, GONG Meng SEISMOLOGY AND GEOLOGY    2025, 47 (1): 49-63.   DOI: 10.3969/j.issn.0253-4967.2025.01.004 Abstract （993）   HTML （30）    PDF（pc） （3649KB）（336）       Knowledge map    Save On January 7, 2025, at 09:05 Beijing Time, an MS6.8 earthquake struck Dingri County in Shigatse City, Xizang, as reported by the China Earthquake Networks Center. The earthquake occurred at 28.50°N, 87.45°E with a hypocentral depth of 10km, resulting in significant casualties and economic losses. In the immediate aftermath, major earthquake research institutions and seismologists, both domestic and international, promptly released the focal mechanism solution, providing crucial data for understanding the earthquake's origin and its seismogenic structure. However, the two nodal planes of the focal mechanism, derived from a double-couple source model, are equivalent, necessitating additional data or methodologies to distinguish the actual seismogenic fault plane. The parameters of the seismogenic fault are fundamental for the accurate calculation of ground motion maps, and they provide key information for seismic hazard assessment and post-earthquake rapid response guidance. Therefore, it is imperative to identify the seismogenic fault plane for the given focal mechanism solution. This study employs the tectonic stress field in the source region of the Dingri earthquake to calculate the instability coefficients of the two nodal planes, selecting the most unstable plane as the actual seismogenic fault. This method is based on the tectonic stress field to identify the seismogenic fault plane in the two nodal planes of the focal mechanism solution. The approach is applied to identify the seismogenic fault plane of the Dingri earthquake and nearby historical seismic events. Using the Global Centroid Moment Tensor(GCMT)focal mechanism solution, the study inverts the shallow tectonic stress field in the source region. The results reveal the maximum principal compressive stress axis is nearly vertical, and the maximum principal tensile stress axis is nearly horizontal with a strike orientation of E-W, which is a normal faulting stress regime. The stress field result is consistent with the normal faulting characteristics of the regions main fault structures. The seismogenic fault for the Dingri 6.8 earthquake is the one-striking southward and dipping westward nodal plane of the focal mechanism solution, determined to be a normal fault. Thus, we can infer that the seismogenic fault is the Dengmocuo Fault. In addition, the identification of the seismogenic fault for the historical earthquakes in the Dingri area shows that the fault is characterized by a southward strike and westward dip, with dip angles ranging from 37° to 48°, and the fault type is normal faulting. Identifying the seismogenic fault plane in the nodal planes of the focal mechanism solution based on the tectonic stress field, this study accurately identifies the seismogenic faults associated with the Dingri earthquake and surrounding historical events. It contributes seismological evidence for understanding the seismogenic structure of the region. It offers valuable insights for future research on seismogenic structures, particularly the determination of seismogenic faults of small and medium-magnitude earthquakes. Table and Figures | Reference | Related Articles | Metrics

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RECONSTRUCTION OF THE PALEOCONE MORPHOLOGY OF CHANGBAISHAN TIANCHI VOLCANO MA Chen-yu, CHENG Tao, WAN Yuan, PAN Bo, ZHOU Bing-rui, YAN Li-li SEISMOLOGY AND GEOLOGY    2024, 46 (6): 1248-1262.   DOI: 10.3969/j.issn.0253-4967.2024.06.002 Abstract （902）   HTML （25）    PDF（pc） （5289KB）（296）       Knowledge map    Save Calderas, large basin-shaped landforms created by massive explosive eruptions, leave behind “pot-like” structures that can provide essential insights into the history and processes of volcanic development and associated hazards. The Changbaishan Tianchi caldera, located on the Sino-North Korean border in eastern Jilin Province, China, is one of the best-preserved large Cenozoic composite active volcanoes in China. This caldera, close to the Wangtiane and Baotaishan volcanoes to the south and southeast, sits atop a basalt plateau, reaching a peak elevation of 2 749m. Its formation involved multiple phases of overflow eruption activities, followed by caldera collapse due to explosive eruptions and pressure loss within the crustal magma chamber during the late Pleistocene. Over time, glaciers and flowing water have sculpted its surroundings, creating U-shaped valleys along the caldera rim. The structure and formation processes of its paleocone have thus attracted significant attention. In this study, we drew from reconstruction techniques applied to similar calderas globally. Starting with a focus on the volcanic cone profile, we identified large-scale stratovolcanoes with symmetrical cone shapes akin to Changbaishan Tianchi for comparison. Using high-resolution stereo imagery, we extracted a Digital Elevation Model(DEM)with remote sensing software. From these DEMs, we performed detailed topographic analysis, calculating and statistically modeling geomorphological parameters, which allowed us to develop a three-phase empirical model of cone topography. Applying a moving surface algorithm in MATLAB, we generated surface equations for each volcano profile, revealing quantitative relationships between pixel position, coordinates, and elevation in 3D geographic space. We then used ArcGIS's Kriging interpolation method to create a DEM of the reconstructed cone of Changbaishan Tianchi volcano, allowing us to approximate the original cone structure. The results estimate the original Changbaishan Tianchi cone reached a height of 4, 100m, with a crater diameter of about 390m and a depth of 170m. The cone displayed a funnel-like structure at the summit, with slopes characteristic of stratovolcanoes. The inner edge of the cone had a relatively uniform slope, while the upper outer edge was steep, averaging 27°, and the lower outer slope angle decreased to an average of 18.5°. These parameters align with typical stratovolcano profiles. The explosive eruptions and subsequent cone collapse are estimated to have led to a volume loss of approximately 28.92km3. This paleocone reconstruction of Tianchi volcano enhances our understanding of the history of the development and evolution of Tianchi volcano, contributing valuable data for reconstructing similar caldera cones and examining eruption mechanisms within the Changbaishan volcanic field. Moreover, this study provides critical information for analyzing the geological history of Tianchi volcano, including the formation of glacial landforms and processes related to eruptions and natural disasters. Table and Figures | Reference | Related Articles | Metrics

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SURFACE RUPTURE INTERPRETATION AND BUILDING DAMAGE ASSESSMENT OF XIZANG DINGRI MS6.8 EARTHQUAKE ON JANUARY 7, 2025 ZOU Jun-jie, SHAO Zhi-gang, HE Hong-lin, GAO Lu, XU Yue-yi, DOU Ai-xia, LIANG Ze-yu SEISMOLOGY AND GEOLOGY    2025, 47 (1): 16-35.   DOI: 10.3969/j.issn.0253-4967.2025.01.002 Abstract （891）   HTML （32）    PDF（pc） （18854KB）（415）       Knowledge map    Save On January 7, 2025, at 9:05 AM, a 6.8-magnitude earthquake struck Dingri County, Shigatse City, Xizang, at a depth of 10km. The maximum intensity of the earthquake reached Ⅺ degrees. This study provides a comparative analysis of pre- and post-earthquake remote sensing images using GF-2 satellite data. The results identify the Dengmecuo fault as the primary seismogenic fault for the earthquake. Surface ruptures exhibit distinct geometric variations between the northern and southern segments. The northern segment, approximately 3km in length, features a relatively simple geometry with a narrow rupture width, forming a “concentrated rupture” pattern characterized by continuity. In contrast, the southern segment, approximately 12km long, displays a more complex geometry with a wider rupture width, resulting in a “diffuse rupture” pattern marked by discontinuities. Statistical analysis of building collapses and damage in 28 administrative villages near the epicenter shows that the severity of impact follows this order: Changcuo township, Cuoguo township, and Quluo township. Affected villages were classified based on their geological and geographical conditions, revealing that the earthquake's impact diminished in the following sequence: areas near the micro-epicenter, lake regions adjacent to the surface rupture zone, and bedrock mountainous areas far from the epicenter and rupture. Coseismic surface rupture analysis reveals two fault segments near Dengmecuo Lake that did not rupture. Considering the unilateral rupture pattern from south to north and the distribution of aftershocks, it is suggested that the unruptured southern segment may pose a greater seismic hazard. At a regional scale, normal faults within the fault system, including the Quluo, Dengmecuo, Guojia, and Dingjie faults, all exhibit aftershock activity. Given the recent release patterns of moderate-to-strong earthquakes, special attention should be given to the seismic risk associated with the Quluo and Dingjie faults. Finally, based on the geographical conditions, seismogenic structures, and seismic damage patterns, this study offers strategies for mitigating seismic risks in high-altitude, high-latitude regions with diverse geological and geomorphological features, diffuse fault deformation patterns, and populations of ethnic minorities. Table and Figures | Reference | Related Articles | Metrics

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SOURCE RUPTURE MECHANISM AND STRESS CHANGES TO THE ADJACENT AREA OF JANUARY 7, 2025, MS6.8 DINGRI EARTHQUAKE, XIZANG, CHINA YANG Jian-wen, JIN Ming-pei, YE Beng, LI Zhen-ling, LI Qing SEISMOLOGY AND GEOLOGY    2025, 47 (1): 36-48.   DOI: 10.3969/j.issn.0253-4967.2025.01.003 Abstract （791）   HTML （46）    PDF（pc） （6115KB）（306）       Knowledge map    Save According to the official determination of China Seismic Network, at 09:05 on January 7, 2025, an MS6.8 earthquake(hereinafter referred to as Dingri earthquake)occurred in Dingri County(28.50°N, 87.45°E), Shigatse City, Xizang, with a focal depth of 10km. The earthquake occurred in the southern part of the Qinghai-Xizang Plateau, which is located in the intersection area of the Shenzha-Dingjie rift and the south of Xizang detachment system. The Dengmecuo fault(about 11km)is the closest to the earthquake, and the focal mechanism is tensile rupture. The earthquake had high magnitude, high intensity and shallow source, and the towns and villages in the epicenter area were relatively concentrated. In addition, the landform type of the epicenter and the surrounding area is a river alluvial plain, and the soil is soft, which amplifies the earthquake damage effect. Due to the comprehensive superposition of various factors, the earthquake caused severecasualties and building damage. The Dingri earthquake is a shallow-source normal-fault earthquake. The ground vibration and building(structure)damage caused by the release process of seismic radiation energy are higher than other earthquakes of the same magnitude, and the surface rupture characteristics are more significant. Therefore, the in-depth study of the Dingri earthquake, the acquisition of the co-seismic deformation field and the source sliding model, and the understanding of the earthquake's seismogenic mechanism and dynamic process can provide scientific and technological support for seismic damage assessment and secondary disaster analysis. In addition, based on the fault slip model, the Coulomb stress change in the surrounding area caused by co-seismic dislocation can be calculated, which is of great significance for the scientific evaluation of the future seismic risk and potential seismic disaster risk in the adjacent area. The Dingri earthquake occurred at a high altitude area, with an average elevation of about 4471m within 10km near the epicenter. The harsh natural conditions and the surrounding GNSS and strong seismic stations are scarce. Therefore, SAR images have become an important data source for obtaining the coseismic deformation of the earthquake and inversion of fault slip distribution. In this paper, based on the ascending and descending SAR image data before and after the Dingri earthquake taken by the Sentinel-1A satellite of the European Space Agency, the co-seismic deformation field of the Dingri earthquake was obtained by D-InSAR technology. On this basis, the source sliding model of the earthquake was jointly inverted based on the coseismic deformation data of the ascending and descending orbits, and the Coulomb stress variation characteristics of the surrounding area caused by the co-seismic dislocation were calculated. The deformation characteristics of the Dingri earthquake, the source rupture mechanism and the stress adjustment effect on the adjacent area are analyzed and discussed. Form the following understanding: (1)The results of the coseismic deformation field of the Dingri earthquake obtained based on the D-InSAR technology ' two-track method ' show that the long axis of the coseismic deformation field of the ascending and descending orbits is nearly NS-trending. The coseismic deformation is characterized by two obvious deformation areas in the east and west and a butterfly-like stripe pattern. The LOS deformation of the ascending and descending orbits is between -0.58~0.33m and -0.80~0.66m, respectively. (2)Based on the coseismic deformation data of ascending and descending orbits, the moment magnitude of the Dingri earthquake obtained by joint inversion is MW7.06 by using the SDM layered model method. The rupture process of the earthquake shows a unilateral rupture characteristic from the initial rupture point to the north along the fault. The fault dislocation is a standard fault mechanism with a little strike-slip component. The length of the main rupture zone of the seismogenic fault is about 55km, and the slip distribution is concentrated in the depth range of 0~15km underground. The maximum slip is 4.25m, which occurs at a depth of 8.6km underground. The main rupture zone of the earthquake has reached the surface, located about 35~53km north of the epicenter along the strike, and the potential surface rupture length is about 18km. (3)The results of the change in coseismic Coulomb stress show that the Dingri earthquake led to a decrease in coseismic Coulomb stress on both sides of the seismogenic fault. The Coulomb stress at the north and south ends of the fault rupture section and its surrounding areas increases significantly, and the loading amount is much larger than the earthquake-triggering threshold of 0.01MPa. There is a possibility of further felt aftershocks in these areas in the future. Table and Figures | Reference | Related Articles | Metrics

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STUDY ON SEISMOGENIC TECTONICS OF THE 2025 MYANMAR MS7.9 EARTHQUAKE XU Bin-bin, ZHANG Yi-peng, LU Le-jun, TIAN Qing-ying, YANG Xue, WANG Yang, ZHANG Pei-zhen SEISMOLOGY AND GEOLOGY    2025, 47 (2): 649-670.   DOI: 10.3969/j.issn.0253-4967.2025.02.20250089 Abstract （636）   HTML （41）    PDF（pc） （13633KB）（314）       Knowledge map    Save According to the China Earthquake Networks Center, an MS7.9 earthquake(hereafter referred to as the Myanmar earthquake)struck the Mandalay region of Myanmar(21.85°N, 95.95°E)on March 28, 2025, at a focal depth of 30km. The earthquake occurred along the central segment of the Sagaing Fault and was characterized by a right-lateral strike-slip rupture, generating a ~350km-long surface rupture zone with a maximum coseismic horizontal displacement of 6 meters. The event caused extensive damage to buildings and varying degrees of destruction to infrastructure, including roads and bridges. Situated in a critical tectonic region where the Indian Plate obliquely converges with the Eurasian Plate, the Myanmar earthquake offers valuable insights into plate boundary deformation processes. Detailed analysis of this event enhances our understanding of the deformation mechanisms along the Myanmar plate boundary and provides essential constraints for seismic hazard assessment along the southeastern margin of the Eurasian Plate. This research holds scientific significance for elucidating continental lithospheric deformation in response to oblique plate convergence. The findings contribute to regional early warning strategies and disaster mitigation efforts and offer a valuable reference for seismic risk studies in comparable tectonic settings worldwide. This study integrates Global Navigation Satellite System(GNSS)data from across the Sagaing Fault region, establishing a comprehensive GNSS velocity field for Myanmar and addressing previous gaps in coverage along the fault’s southern segment. Using multiscale spherical wavelet analysis and GNSS velocity profiles, we examine the deformation characteristics of the region. We calculate the slip rate deficit distribution along the Sagaing Fault and assess postseismic Coulomb stress changes. Combined with historical seismicity data, we investigate the seismogenic structure and stress perturbations in surrounding areas. The key findings are as follows: (1)The Myanmar MS7.9 earthquake was a right-lateral strike-slip event along the central Sagaing fault. The region is affected by the northeastward oblique convergence of the Indian Plate and southeastward extrusion of crustal material from the Tibetan plateau, resulting in strong north-south shear and east-west shortening. The Sagaing fault accommodates most of this deformation, with a rapid right-lateral slip rate of approximately 21~22mm/a. (2)High-resolution GNSS velocity profiles indicate significant fault locking at depths of 15~25km along the Sagaing Fault. The slip rate deficit analysis reveals a high locking ratio across the fault, indicating elevated seismic potential. Notably, the central segment shows lower seismic moment accumulation compared to the northern and southern segments, forming a ~300km-long seismic gap since 1900, capable of generating earthquakes exceeding magnitude 7.5. (3)Coulomb stress modeling suggests that the earthquake significantly altered the regional stress field. Stress accumulation zones were identified at both ends of the Sagaing fault and in the central Shan Plateau to the east. These regions of increased stress transfer and loading exhibit heightened potential for future large earthquakes, underscoring the need for enhanced seismic monitoring. Table and Figures | Reference | Related Articles | Metrics

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PETROGENESIS OF THE MOST RECENT VOLCANISM IN MAINLAND CHINA: EVIDENCE FROM THE ISOTOPIC CHARACTERISTICS OF ASHIKULE VOLCANIC ROCKS MAO Xiang, BAI Xiang, YU Hong-mei, ZHAO Bo, CHEN Hui-zhi SEISMOLOGY AND GEOLOGY    2024, 46 (6): 1227-1247.   DOI: 10.3969/j.issn.0253-4967.2024.06.001 Abstract （555）   HTML （40）    PDF（pc） （6150KB）（254）       Knowledge map    Save The Ashikule Volcanic Cluster(AVC), located in the western Kunlun region of the northwestern Tibetan plateau, represents the most recent volcanic activity on Mainland China. This volcanic cluster, which erupted continuously from the Pleistocene to the Holocene, predominantly produced trachyandesites and trachytes, with minor occurrences of phonotephrites, basaltic trachyandesites, and rhyolites. In this study, we present zircon U-Pb-Lu-Hf and whole-rock Sr-Nd-Pb isotopic analyses for volcanic rock samples from AVC. By integrating these data with petrographic, geochronological, and geochemical findings from Yu et al.(2020), we propose further constraints on the petrogenesis of the volcanic rocks and the geodynamic evolution of the western Kunlun region from the Pleistocene to the Holocene. Zircon U-Pb-Lu-Hf isotopic analyses were conducted on five samples: Two trachyandesitic (515-01 and 518-14), two trachytic (521-1 and 521-4), and one rhyolitic(517-B-03). Together with previous 40Ar/39Ar dating, the magmatic zircon grains reveal negative εHf(t) values ranging from -8.8 to -4.4 for the trachyandesitic samples, -8.6 to -5.7 for the trachytic samples, and -9.1 to -6.7 for the rhyolitic sample, suggesting an enriched magma source. The trachyandesitic samples also contain Paleozoic to Mesozoic zircons (165-2 352Ma) with characteristics such as small oval shapes or core-rim structures, indicating that they are inherited zircons. These inherited zircons display εHf(t) values from -3.1 to 9.8, suggesting the involvement of metasedimentary components in the magma source. Whole-rock Sr-Nd-Pb isotopic analyses were conducted on eight samples(four trachyandesitic, three trachytic, and one rhyolitic), revealing 87Sr/86Sr ratios of 0.709 395-0.711 441 and 143Nd/144Nd ratios of 0.512 154-0.512 355. In the 143Nd/144Nd-87Sr/86Sr diagram, these samples plot to the right of the EM Ⅰ region in the fourth quadrant, indicating a relationship with EM Ⅱ-type magmatism. The samples exhibit 207Pb/206Pb ratios of 15.652-15.673 and 206Pb/204Pb ratios of 18.681-18.754, aligning with EM Ⅱ-type and lower crust-derived magmatism on the 207Pb/204Pb-206Pb/204Pb diagram. In the Rb/Nd-Rb diagram, the Ashikule volcanic rocks display an oblique distribution, indicating processes of partial melting or magma mixing, which is further supported by their alignment with the mixing trend on the 1/V-Rb/V diagram. Geochemical modeling results suggest that the Ashikule volcanic magmas formed primarily through a magma mixing process. Previous electron probe microanalysis studies have identified reverse zoning in plagioclase and orthopyroxene phenocrysts, providing additional evidence for magma mixing in the magma chamber. Consequently, these data reveal that Ashikule volcanic magmas originated from a mixing process between EM Ⅱ-type mantle-derived basic magmas and intermediate to acidic magmas from partial melting of ancient continental materials. Considering the tectonic setting of the Tibetan plateau, we propose that Ashikule volcanic activity likely formed in a subduction-dominated environment from the Pleistocene to the Holocene. Table and Figures | Reference | Related Articles | Metrics

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Characteristics of Pb isotopes of fluvial detrital K-feldspar in the Yellow River Basin and its geological significance as provenance tracing SEISMOLOGY AND EGOLOGY    0, (): 0-0.   Abstract （494）            Knowledge map    Save Tracing sediment sources in the Yellow River Basin is of great importance for understanding the coupling relationship between uplift and denudation of the Tibetan Plateau and marine sedimentation in the western Pacific margin. K-feldspar is one of the common rock-forming minerals in river sediments, and its Pb isotopic compositions are effective tools in the provenance tracing research of large rivers. However, this research has not been carried out in the Yellow River Basin. In situ Pb isotopes of 967 K-feldspar samples were obtained by laser erosion inductively coupled plasma mass spectrometer(LA-ICP-MS). The results of 206Pb/204Pb and 208Pb/204Pb ratios showed that the Pb isotopic compositions of K-feldspar grains in the Yellow River, Daxihe River and Huangshui River in Maduo-Tongde section were significantly different from those in Lanzhou section. The Pb isotopic composition of K-feldspar in Lanzhou section of the Yellow River is consistent with that in Bayannur section of the Yellow River, which are influenced by similar eolian provenance. K-feldspar grains from the Yellow River and Fen River in the Jinshan-Shaanxi Gorge are mainly from the Loess Plateau. The K-feldspar grains in the Weihe River mainly derive from the Qinling Mountains. The Pb isotopic compositions of K-feldspar grains in the Kaifeng and Lijin sections of the Yellow River are different to those in the upper reaches of the Yellow River and the North China Plate, but similar to those in the middle reaches of the Yellow River. The Loess Plateau plays a leading role in the source of K-feldspar gains in the middle and lower reaches of the Yellow River. Related Articles | Metrics

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THE DISTRIBUTION AND RESEARCH PROGRESS OF MAIN MUD VOLCANOES IN CHINA WANG Qian, PENG Lai, JIANG Yu-han, ZHOU Qi-chao, GAO Xiao-qi SEISMOLOGY AND GEOLOGY    2025, 47 (1): 90-116.   DOI: 10.3969/j.issn.0253-4967.2025.01.007 Abstract （485）   HTML （22）    PDF（pc） （4618KB）（104）       Knowledge map    Save This paper provides an overview of the distribution and research progress of mud volcanoes in China, and offers a comparative analysis of the physical and geochemical characteristics of mud volcano emissions from various regions. The findings are as follows: Mud volcanoes in China are predominantly located along faults or fault zones, primarily in seismically active regions such as Xinjiang, Tibet, and Taiwan. A comparative analysis of emissions from different regions reveals that the solid components—primarily minerals like quartz and montmorillonite—are similar across locations. The liquid emissions generally exhibit high salinity. Geochemical analysis indicates regional differences in the sources of the emitted mud water: in Xinjiang, it mainly derives from a mixture of ancient sediment pore water and atmospheric precipitation; in Tibet, it originates from deep groundwater and atmospheric precipitation; and in Taiwan, it comes from marine sediment pore water mixed with atmospheric precipitation. In terms of gas emissions, methane is the predominant gas released by most mud volcanoes in the study area, with smaller amounts of ethane, carbon dioxide, and other hydrocarbons. Notably, some mud volcanoes in Taiwan region emit higher concentrations of carbon dioxide and nitrogen, with smaller amounts of methane. Carbon isotope analysis of the emitted gases shows that the methane is of organic origin, as indicated by δ13C1 values. In addition to the geochemical analysis, the microbial communities associated with mud volcanoes are also significant. The origin of methane suggests the presence of methane-producing microbial communities in the surrounding environments of onshore mud volcanoes. These microbes, including aerobic methane-oxidizing bacteria and anaerobic methane-oxidizing archaea, play a role in the formation of the emitted gases. In particular, these microorganisms are found in the soil environments of mud volcanoes in eastern Taiwan region, Wusu(Xinjiang), and Dushanzi(Xinjiang), where they use carbon dioxide as a carbon source to produce methane. In submarine mud volcanoes, the eruption process provides conditions for the growth of marine microorganisms, including methane-producing bacteria. Mud volcanoes are generally triggered by four main factors: volcanic activity, tectonic activity, sedimentary processes, and anthropogenic influences. Given their prevalence in seismically active zones, the activity of mud volcanoes is often induced by seismic events. Eruptions typically result from increased pore pressure within the surrounding rock layers. Significant physical and chemical anomalies, including elevated gas emissions and changes in the height of the mud surface, are observed before and after seismic events. For example, following the establishment of a real-time monitoring system for the Wusu mud volcano in Xinjiang in 2011, multiple earthquakes in the area were associated with changes in the mud volcano's liquid level and increased emissions of methane(CH4)and carbon dioxide(CO2), which gradually returned to background levels post-earthquake. These geochemical changes have been observed in other regions as well, such as the hydro geochemical changes in the north Tianshan Mountains, following the Xinyuan MS6.6 earthquake. These observations suggest that mud volcano emissions may serve as indicators of seismic activity. Long-term monitoring of mud volcanoes could potentially offer a means of predicting seismic events. Table and Figures | Reference | Related Articles | Metrics

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CRUSTAL DEFORMATION CHARACTERISTICS AND RELEVANT SEISMIC HAZARD OF THE TAIYUAN BASIN CHEN Qian, ZHANG Zhu-qi SEISMOLOGY AND GEOLOGY    2025, 47 (1): 189-213.   DOI: 10.3969/j.issn.0253-4967.2025.01.012 Abstract （452）   HTML （24）    PDF（pc） （9962KB）（111）       Knowledge map    Save The Taiyuan Basin(TB) is located at the middle part of the Shanxi Graben belt(SGB), which is the tectonic boundary between the Ordos active block in the West and the North China Plain in the East. The SGB comprises several echelon left-stepping depression basins lining up in NNE direction. Previous studies of active tectonics and crustal kinematics indicate that the present deformation of the SGB is controlled by the NNE dextral shear and NW extension between the blocks on both sides of it, but how the shear and extension are accommodated by basins remains in question. To answer the question, researchers in active tectonics have made more effort to investigate the slip type and rate of faults bounding basins. By contrast, inadequate attentions were paid to the kinematic characteristics of the internal deformation within basins. Recent studies on focal mechanisms find that not only normal slip earthquakes but also strike-slip earthquakes, which account for a major proportion of the whole seismicity, occur in the depression basins of the SGB.As can be seen, faulting with dominating normal slip on basin boundary faults cannot easily and reasonably explain how the SGB deforms at present. To comprehensively understand the present deformation mechanism of the SGB, further exploration is needed, which should be based on both the deformation characteristics of basin boundary faults and the kinematic characteristics of the relevant blocks including basins. Compared with other basins in the SGB, the TB has relatively simple features in tectonics, which an explicit kinematic model may describe. Therefore, the TB is potentially proper to demonstrate how basins deform in the SGB. Developing typical tectonics like other basins of the SGB, the TB behaves oddly at the same time in terms of seismicity. Constituting the middle segment of a large-scale active block boundary and developing active faults reaching the middle and lower crust, this tectonic basis jointly imply the TB is eligible for the occurrence of large earthquakes. However, the historical record of earthquakes with a magnitude greater than 7 is lacking in the TB.In contrast to that, several earthquakes with a magnitude of 7 or even up to 8 have occurred in the last thousand years in the Xinding Basin and the Linfen Basin adjacent to the TB.So far, it is still uncertain how possible and how urgent a big earthquake could strike the TB in the future. To address this question, a thorough evaluation of the accumulation state of seismic energy on the boundary faults of TB is necessary. Modeling the kinematics of block and fault with constraints from GPS velocity usually gives the spatial distributions of slip rate and locking ratio on faults, and also Euler rotation velocities and strain rates of blocks. However, due to the azimuthal heterogeneity and the sparsity in the distribution of GPS stations, the result of modeling block-fault kinematics sometimes concerns trade-offs between variables, and the optimal solution may be discrepant with the given tectonic knowledge. Furthermore, for the fault with a low dip angle, the overlap of surface strain due to faulting and that due to internal deformation of the hanging wall block could be large, which may aggravate the mentioned trade-off and discrepancy. As the block-fault kinematic model related to TB involves the above issues, appropriate conditions may be carefully selected to enhance the constraints of modeling. In this study, a three-dimensional geometric model of two boundary faults of the TB is constructed based on the data from earthquake geology and deep exploration. A kinematic model of the blocks and the boundary faults relating to the TB is constructed based on the geometric model. According to previous studies on regional tectonics, this study attempted to obtain appropriate a priori information to provide better constraints on the modeling. Several strategies of modeling were designed based on the characteristics of a priori information. Constrained by a priori conditions, the GPS velocities at 137 sites from two data sources are simulated to get the fundamental kinematic features for the blocks and the boundary faults concerning the TB, which include the vertical axis rotation velocity and translational velocity at the centroid of the TB and the blocks in its neighbor, the distribution of locking ratio on the fault planes, and additionally the crustal strain rate within the basin. An apparent optimal model is obtained considering not only its fitting to the GPS velocities but also the good correlation between the observational features of principal axes of strain rate and that from the modeling. The results of the apparent optimal model show that the TB is spinning clockwise, and bearing the internal strain with principal axis orientating in NW.The blocks on the west side and the east side of the TB are both translating toward approximately SE under the stable Eurasian reference frame, but the east block TH is moving faster with more southward component relative to the west block LL.Furthermore, the LL and TH blocks are spinning counterclockwise. As the western boundary of the TB, the Jiaocheng fault is a normal fault with a right-lateral component. In contrast, the Taigu fault, which is on the eastern side of the basin, is a right-lateral fault with a normal component. According to the above features of the apparent optimal model, it is inferred that the combination of the tensional function across the western basin boundary and the strike-slip shearing along the eastern boundary contributes to the clockwise rotation of the TB and also causes the internal NNE dextral shear and NW extension within the basin. The model results also show extensive locking areas on the Jiaocheng fault and the Taigu fault. Taking into account of the relevent research on the recurrence of paleo-earthquakes since the late Pleistocene, the locking status of the fault indicates that the Jiaocheng fault is close to the occurrence of an earthquake greater than M7.5.In contrast, the Taigu fault has accumulated enough energy for an earthquake around M6.7, which appeals to attention and further studies on the possible occurrence of strong earthquakes in the vicinity of the TB. Table and Figures | Reference | Related Articles | Metrics

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CRUSTAL DEFORMATION CHARACTERISTICS AND PROBABILITY PREDICTION OF STRONG EARTHQUAKE RISK IN XINJIANG AND ITS ADJACENT REGION CHEN Chang-yun, YIN Hai-quan SEISMOLOGY AND GEOLOGY    2025, 47 (2): 384-404.   DOI: 10.3969/j.issn.0253-4967.2025.02.20240151 Abstract （426）   HTML （32）    PDF（pc） （9921KB）（145）       Knowledge map    Save Based on the GNSS velocity field, we analyzed the present-day crustal deformation characteristics of Xinjiang and its adjacent regions before the January 23, 2024, Wushi earthquake using the spherical least squares configuration method. Based on the fundamental concept of active blocks, Xinjiang and its neighboring areas were divided into 17 active blocks by integrating regional seismic geological data. The slip rates of the boundary fault zones of these active blocks were then calculated using a three-dimensional elastic block model. Based on this block delineation, the study area was further divided into 91 potential seismic hazard zones. We incorporated geodetic observations, including fault strike-slip rates and dilatational strain rates derived from the GNSS velocity field, into the conventional probabilistic forecasting of significant seismic hazards. The relationship between the Wushi 7.1 earthquake and the regional crustal deformation characteristics, as well as the prediction results of the probability of strong earthquakes, was comprehensively analyzed. The direction and magnitude of GNSS velocity field motions in the study area under different dynamical backgrounds are distinctly characterized by zoning. GNSS stations east of longitude 76° move toward the north or northeast, while those on the west side move north or northwest. The velocity field difference is primarily evident on the north and south sides of the Tianshan Mountain. The velocity change of GNSS sites from the Tibetan plateau to the Tarim Basin is minor, but it significantly decreases after crossing the Tianshan Mountain, indicating that the Tianshan Mountain tectonics absorb most of the remote effects of the Indo-Eurasian plate collision. The principal strains obtained from the least-squares configuration results reveal that the extrusion characteristics are most prominent near the western section of the Southern Tianshan Mountains and the Altyn Tagh fault zone. In the western section of the Southern Tianshan Mountains, the direction of the principal compressive strains is perpendicular to the tectonic direction in the region. This suggests that the region is primarily influenced by a force perpendicular to the tectonic direction, resulting in the predominant retrograde movement of major fault zones in the area. Moreover, in addition to the western section of the Southern Tianshan Mountains, the region with a greater main compressive strain is the Altyn Tagh fault zone. The direction of the main compressive strain intersects obliquely with the Altyn Tagh fault zone, suggesting that the force background is linked to the left-lateral reverse slip movement of the Altyn Tagh fault zone. The results derived from the inversion of the three-dimensional elastic dislocation model reveal that the motion features of the main active faults within the study area indicate a predominance of dextral slip along the northwest-trending fault zones in the Tianshan region, while sinistral slip motion is primarily observed along the northeast-trending or northeastern fault zones. Apart from the Altyn Tagh fault zone, the strike slip rate of the dextral-slip fault zones is notably higher than that of the sinistral-slip fault zones. The fault zones at the northern edge of the Junggar Basin and the major faults in the Tianshan region are primarily characterized by extrusion movements. The extrusion rate of the fracture zones in the South Tianshan Mountain is higher than that in the North Tianshan Mountain. Specifically, the west section of the Keping fault zone and the west section of the Nalati fault zone exhibit the most prominent extrusion movements. The study area has been divided into 91 potential seismic hazard zones based on block delineation and the findings from previous research. The slip rates and regional surface strains of the major faults obtained from the inversion are utilized in classical probabilistic predictions to derive quantitative results regarding the strong earthquake hazard in the study area over the next 50 years. The results indicate that the strong earthquake hazard is primarily concentrated in the western section of the Southern Tianshan region. This includes areas such as the north-east or nearly east-west-trending Maidan fault, the Nalati fault, and the Usun Ridge Fault, as well as the north-west-trending Talas-Fergana fault zone and the north-west section of the Kyzyltau fault zone. Furthermore, the probability of strong earthquakes is elevated in the northern Luntai fault compared to the surrounding faults. In the northern Tianshan region, areas with relatively high probabilities of strong earthquakes include the Fukang fault and the western section of the Bogda fault. The seismic mechanism solution reveals that the M7.1 Wushi earthquake was a thrust earthquake, aligning with the characteristics of the Maidan fault zone. In this zone, the seismogenic fault is primarily influenced by extrusion motion. The Wushi earthquake occurred in the Maidan fault zone, situated at the border of the high shear strain rate zone and the high probability hazard zone. This occurrence validates the effectiveness and accuracy of the probabilistic prediction method. Table and Figures | Reference | Related Articles | Metrics

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STUDY ON THE SLIP RATE OF THE BAISHA RIVER SEGMENT IN THE YINGXIU-BEICHUAN FAULT IN THE LONGMENSHAN FAULT ZONE HUA Chun-yu, SHI Feng, WEI Zhan-yu SEISMOLOGY AND GEOLOGY    2024, 46 (6): 1295-1313.   DOI: 10.3969/j.issn.0253-4967.2024.06.005 Abstract （424）   HTML （30）    PDF（pc） （7758KB）（200）       Knowledge map    Save The tectonic belt stretches approximately 400km from Lushan County to Wenchuan County in an east-west direction. The Longmenshan fault zone can be geometrically divided into several sections, including the Houshan Fault, the Central Fault, the Qianshan Fault, and the Foreland Basin(Chengdu Plain)Deformation Zone. The Central Fault is the main segment of the active tectonic belt in the Longmenshan region, and the Yingxiu-Beichuan Fault is one of the most active segments within this central section. The Yingxiu-Beichuan Fault has experienced numerous moderate and strong earthquakes throughout its history, including the Wenchuan earthquake 2008. The 2008 Wenchuan earthquake was ahigh destructive natural disaster that profoundly impacted the Chinese mainland, leading to significant economic losses and casualties. This earthquake caused extensive building collapses, leading to the loss of tens of thousands of lives, and triggered severe secondary geological disasters such as landslides, rockfalls, and mudflows, severely affecting the normal operation of transportation and communication infrastructure. The Yingxiu-Beichuan Fault was one of the key surface rupture zones during this earthquake. However, there is still some uncertainty about the slip rate of this fault. The Baisha River segment examined in this paper is located in the southern part of the Yingxiu-Beichuan Fault, measuring approximately 14km long. This area contains 14 fractures of varying lengths and complex geometric structures, forming a fracture zone that reaches a maximum width of nearly 300m. The overall orientation of the rupture zone is about 50 degrees; however, the orientation of each small secondary rupture varies, with differences ranging from 0 to 90 degrees. The coseismic displacement along the Baisha River section displays complexity and diversity. The thrust movement primarily occurs on the northern and western walls, with some local thrust faults. Additionally, the strike-slip motion is predominantly right-lateral, exhibiting a maximum horizontal displacement of approximately 4.8m, although some local areas show left-lateral displacement. Previous studies have employed various techniques, such as geology and geodesy, resulting in a wide range of slip rate estimates from 0.07mm/a to 1.1mm/a. The slip rate of fault is a crucial factor for analyzing the characteristics of fault activity and for studying regional kinematics and dynamic mechanisms. According to river terrace longitudinal profiles estimates, the fault has a vertical slip rate of about 0.3mm/a to 0.6mm/a. Estimates based on displaced landforms indicate a vertical slip rate between 0.07mm/a and 1.1mm/a. According to GPS observations, the horizontal slip rate in the Longmenshan fault zone has a limit of 2mm/a, but the slip rate of individual faults is lower than 0.7mm/a. In recent years, remote sensing techniques have been extensively utilized to study surface rupture zones, particularly during significant seismic events. This paper primarily employs aerial and QuickBird satellite images captured before and after the earthquake. The resolution of the aerial images is nearly 1m, while the QuickBird satellite images have a resolution of 0.6m, both of which allow for precise interpretation of tectonic landforms. River terraces consist of terraced units, including terraced surfaces, steep terraces, terrace fronts, and terrace backs. As geomorphic markers that are relatively easy to identify and measure, river terraces are among the most essential geomorphic units in the quantitative study of active tectonics. They also serve as crucial geological relics documenting Quaternary tectonic movements and climate changes. By examining river terraces and their deformations, researchers can discuss the timing and scale of tectonic activity, making this a long-term area of research. This paper focuses on the Baisha River section, situated in the southern part of the Yingxiu-Beichuan Fault. We employed geological and geomorphological methods along with optically stimulated luminescence dating, remote sensing interpretation, field investigations, and data analysis to assess the slip rate of the Baisha River section of the Yingxiu-Beichuan Fault within the Longmenshan fault zone. Additionally, we analyze the spatio-temporal variation characteristics of this slip rate. This study constrains the slip rate of the Baishahe segment of the Yingxiu-Beichuan Fault in the Longmenshan fault zone using 10 terrace cross-sections and terrace ages. The results indicate that the Yingxiu-Beichuan Fault Baisha River segment has a vertical slip rate since the Late Pleistocene ranges from(0.10±0.02)mm/a to(0.30±0.05)mm/a. Considering that only one event, the 2008 Wenchuan earthquake, is associated with the T1 terrace, we believe the calculated rate based on the dislocation and age of the T1 terrace may significantly deviate from reality. If we exclude the sliding rate of the T1 terrace, the vertical slip rate since the late Quaternary ranges between(0.10±0.03)mm/a and(0.30±0.05)mm/a. The linear fitting results indicate that the average vertical sliding rate since the late Quaternary is approximately 0.19mm/a. These findings provide fundamental data for understanding the seismogenic structure of the Wenchuan earthquake and the overall characteristics of the Longmenshan fault zone, as well as for assessing its long-term seismic hazard. Table and Figures | Reference | Related Articles | Metrics

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THE STUDY OF FINE CRUSTAL STRUCTURE OF THE SOUTHERN MARGIN OF TAIHANG MOUNTAIN BY DEEP SEISMIC REFLECTION PROFILE FENG Shao-ying, LIU Bao-jin, ZUO Ying, JI Ji-fa, TAN Ya-li, DING Kui, WU Quan SEISMOLOGY AND GEOLOGY    2025, 47 (1): 267-283.   DOI: 10.3969/j.issn.0253-4967.2025.01.016 Abstract （408）   HTML （7）    PDF（pc） （8370KB）（124）       Knowledge map    Save To investigate the fine crustal structure and tectonic characteristics of the southern margin of the Taihang Mountain, we conducted a deep seismic reflection survey along a 120km profile between Huixian and Changyuan. Regarding data acquisition, we applied a geometry with a 25m group interval, 800 recording channels, and more than 60-fold coverage. The seismic wave explosion utilized a dynamite source of 30kg, with a hole depth of 25m. The shot interval was 200m. In data processing, the most critical aspect was improving the signal-to-noise ratio. The data processing workflow mainly included static correction(first-break tomography method), multi-type and multi-method denoising before stacking, amplitude compensation, surface-consistent predictive deconvolution, several iterations of velocity analysis and residual static correction, dip movement correction, and post-stack finite-difference migration. A seismic section with a high signal-to-noise ratio was obtained, revealing the fine crustal structure along the survey line. The crustal structure in the section exhibits clear stratification, with crustal thickness ranging from approximately 33.5km to 42.7km. The crust contains distinct reflective structures from top to bottom, being thinner in the southeast and thicker in the northwest. The upper crust is about 13.3km thick in the southeast and approximately 20.1km in the northwest. The basement reflection deepens from west to east along the profile. In the southern Taihang Mountain, the depth of the basement reflection is about 1.0~1.5km in the northwest side of the Tangyin fault depression. Within the Tangyin fault depression, the basement reflection depth is approximately 3.5~4.0km. East of stake 56.0km, the basement surface tilts eastward, with its deepest point reaching approximately 8.0~10.0km. The lower crust exhibits strong reflective properties, consisting of a series of high-energy reflection waves, with inclined and arc-shaped strong reflections indicating significant heterogeneity in lower crust composition. The Moho shows relatively strong reflected energy and good lateral continuity. It gradually deepens from southeast to northwest, with its shallowest depth at approximately 33.5km. Numerous fault structures are observed along the deep seismic reflection profile. We identified ten faults in the upper crust and one deep fault. In the northwest section of the profile, three faults form a Y-shaped distribution. The upper part of the fault disrupts the bottom boundary of the Q+N strata and disappears downward into the upper crust. The Tangdong fault is the main controlling boundary fault of the Tangyin fault depression. It cuts through the shallow sedimentary strata and basement reflection wave groups as a shovel-shaped normal fault and disappears into the upper crust. The Tangxi fault and Tangzhong fault merge into the Tangdong fault at depths of approximately 8.0~10.0km and 5.0~6.0km, respectively. The Changcun fault and Changyuan fault, located in the eastern section of the profile, appear in the strata beneath the Neogene and terminate at the interface between the upper and lower crust, without cutting through the upper Q+N strata. The Yellow River Fault is a large-scale fault in the Dongpu depression and serves as the eastern boundary fault of the depression. Its shallow section consists of two inclined faults, with the main fault being a northwest-trending normal fault. The deep fault appears as a nearly vertical weak-reflection energy strip on the section or as a discontinuous zone of reflection characteristics, located on the southeast side of the Tangyin fault depression. This fault zone represents a major deep crustal fault. It offsets intracrustal interface reflections, lower crustal reflection bands, and the crust-mantle interface reflection. The deep fault in the crust has become a channel, facilitating the upwelling of deep hot material. The upwelling of deep material, magma underplating, or thermal erosion leads to the tensile extension of the crust and lithospheric thinning, potentially altering crustal structure and material composition. Table and Figures | Reference | Related Articles | Metrics

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DISCOVERY OF A STRONG PALEOSEISMIC EVENT IN THE CHENGHAI-BINCHUAN FAULT ZONE LUO Lin, CHANG Zu-feng, YIN Gong-ming, MAO Ze-bin, HUA Jun, CHEN Gang SEISMOLOGY AND GEOLOGY    2025, 47 (1): 214-234.   DOI: 10.3969/j.issn.0253-4967.2025.01.013 Abstract （374）   HTML （17）    PDF（pc） （23733KB）（114）       Knowledge map    Save The Chenghai-Binchuan fault zone is an active Holocene fault zone approximately 200km in length. The region is characterized by sharply uplifted mountains and canyon landforms, intense erosion, and frequent geological hazards such as collapses, landslides, and debris flows. These factors have obscured the preservation of displaced landforms, making it difficult to identify paleoearthquake relics and hindering the study of paleoearthquakes. The Taoyuan Basin, a tectonic basin formed along the Chenghai-Binchuan fault zone, has undergone extensive land planning and hillside improvements as part of the resettlement efforts linked to the Ludila hydropower project on the Jinsha River. As a result, many artificial slopes have been excavated in the area. Approximately 500m northeast of Chitian village, southwest of Taoyuan town, near the confluence of the Jinsha and Kumu rivers(100.4489°E; 26.1926°N), farmers excavated a large slope for land planning and slope stabilization. This slope, approximately 50m in length and over 10m in height, exposes a relatively continuous sedimentary sequence, including sand and gravel layers. The exposed strata display typical paleoearthquake features, such as fault displacements, seismic wedges, sand veins, and soft sediment deformation, all of which are well-preserved and provide valuable insights into paleoearthquake activity. Paleoearthquake research was conducted through satellite remote sensing interpretation, field geological and geomorphological surveys, slope profile excavation and measurement, detailed stratigraphic description, and chronological testing of sediment samples. The findings are as follows: 1)Two fault sets, striking NW and NE, were identified on the profile. The sedimentary characteristics of each stratigraphic unit, along with the relationships between stratigraphic displacement, marker layer offsets, and features such as colluvial wedges, soft sediment deformation, and sand veins, suggest that a significant earthquake occurred in the area. Radiocarbon dating(AMS 14C)indicates the paleoearthquake event occurred between(5910±30)aBP and(4100±30)aBP. 2)The maximum vertical co-seismic displacement along the fault is 4.0m. Using the empirical relationship between fault displacement and earthquake magnitude, the moment magnitude(MW)is estimated at 7.3, similar to the historical 1515 Yongsheng earthquake(MW7.3). These results fill a critical gap in paleoearthquake data for the Chenghai-Binchuan fault zone and extend the region's paleoearthquake record. This research holds significant practical value for earthquake hazard zoning and seismic risk analysis for major regional projects. Table and Figures | Reference | Related Articles | Metrics

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MOMENT TENSOR INVERSION AND SEISMOGENIC STRUCTURE OF THE 2023 MS5.5 PINGYUAN EARTHQUAKE XU Ying-cai, GUO Xiang-yun SEISMOLOGY AND GEOLOGY    2025, 47 (1): 284-305.   DOI: 10.3969/j.issn.0253-4967.2025.01.017 Abstract （360）   HTML （9）    PDF（pc） （12619KB）（78）       Knowledge map    Save On August 6, 2023, an earthquake with MS5.5 occurred in Pingyuan County, Dezhou City, in Shandong Province, North China. Around the epicenter of the MS5.5 Pingyuan earthquake, obvious earthquake tremors were felt through the regions of Hebei, Henan, Tianjin, Beijing etc. This earthquake also broke the historical record of no earthquake with M≥5.0 within 50km of the epicenter and aroused widespread concern of the society and seismologists. It is urgent to carry out the research on strong earthquake seismogenic structures and seismogenic environments in the basin, which is of great significance to strengthen the seismic tectonic environment exploration and earthquake damage prevention in the weak and rare earthquake areas of the North China Plain. Based on the data of the Regional Seismic Networks around the epicenter, moment tensor solution and centroid depth of the MS5.5 Pingyuan earthquake were determined using the gCAP inversion method, and the stability of moment tensor inversion of the mainshock is evaluated by Bootstrap method. The ML≥1.0 earthquakes of the MS5.5 Pingyuan earthquake sequence were relocated using the double-difference relocation method. By simulation method of the relationship between regional stress regime and focal mechanism, the relative shear stress and normal stress of nodal planes from focal mechanism of the MS5.5 Pingyuan earthquake were obtained. According to the earthquake relocation, the fault plane was fitted, and the seismogenic structure of the earthquake was analyzed. The results indicate: 1)The scalar seismic moment(M0)of the MS5.5 Pingyuan earthquake is 1.97Í1017N·m, while the moment magnitude is MW5.5, and the centroid depth is 16km. The moment tensor solution(Mrr/Mtt/Mpp/Mrt/Mrp/Mtp)is -0.129/1.194/-0.459/0.009/0.336/0.245, while the double-couple(DC), isotropic(ISO) and compensated linear vector dipole(CLVD) components account for 92.40%, 6.25%, and 1.35% of the full moment tensor solution. The focal mechanism of the double-couple solution shows that the MS5.5 Pingyuan earthquake is a strike-slip type natural earthquake event with a little normal fault component, with strike/dip/rake of 222°/71°/-156° and 124°/67°/-21° for nodal planes Ⅰ and Ⅱ. The P-axis azimuth is 84° with plunge angle of 30°, indicating the principal compressive stress in the NEE direction in the focal area, basically consistent with the direction of the main compressive stress of the regional tectonic stress in the North China Plain. The best double-couple solutions of focal mechanism obtained by the Bootstrap method are: strike 220.4°±2.49°, dip 71.5°±4.34°, rake -155.9°±3.58° for the nodal plane Ⅰ, and strike 122.2°±2.83°, dip 67.3°±3.17°, rake -20.2°±4.95° for nodal plane Ⅱ, and centroid depth 16.7±1.10km, reflecting the stability and reliability of moment tensor inversion in this paper. 2)After earthquake relocation, the epicenters of the MS5.5 Pingyuan earthquake sequence mainly show a dominant distribution in the NE-SW direction, with a length of about 15km and a width of about 5km. The epicenter of the MS5.5 Pingyuan earthquake is located in the southwest segment of the earthquake sequence, and the epicenters of the ML≥1.0 earthquake are relatively concentrated on the NE side of the main earthquake, while the distribution of the epicenters of the SW side is relatively sparse. The focal depths of earthquakes with ML≥1.0 are mainly between 8 and 22km, with an average depth of 15.4km. The focal depth profiles demonstrate the fault plane with a dip to the northwest. 3)The regional stress field of North China Craton primarily exhibits NEE-SWW compression and near N-S tensile. The main stress axis direction of the regional stress field is basically consistent with the P-axis of the focal mechanism of the MS5.5 Pingyuan earthquake. The strike-slip component of the focal mechanism of the MS5.5 Pingyuan earthquake shows general consistency with the focal mechanism characteristics of the eastern North China Craton. It is also consistent with the E-W compressive and S-N tensile tectonic stress background of the eastern part of the North China Craton, and the small normal components may be related to the tensile movement of the central and western region of Bohai Bay Basin. The relationship between the focal mechanism and contemporary regional stress regime shows the relative shear stress of 0.860/0.689 for nodal planes I and II under the stress field of the Pingyuan region, and the rake of shear stress for the nodal plane I is close to the rake of focal mechanism. The shear stress on nodal plane I of the focal mechanism is relatively high, reflecting that nodal plane I is very close to the fault shape of the optimal release of relative shear stress of the regional stress field, presenting the source property of right-lateral strike-slip with a small amount of normal component. The fault plane fitting also exhibits the mode of fault movement with right-lateral strike-slip. 4)Combined with the previous studies, it is inferred that the nodal plane I of the focal mechanism for the MS5.5 Pingyuan mainshock is the possible seismic source fault with a dip angle of 71°, and the main seismogenic structure of the Pingyuan earthquake sequence may be a SW-striking blind fault with steep dip to northwest. Under the long-term contemporary principal compressive stress of the tectonic stress field in North China Plain, the MS5.5 Pingyuan earthquake occurred as a right-lateral strike-slip seismic dislocation with a little normal fault component due to the rupture on the nodal plane with optimum shear stress release. It is suggested that the seismogenic structure of the Pingyuan earthquake may be related to the Lingxian-Guanxian fault, a hidden fault system formed by the northern section of the Guanxian fault and the southern section of the Lingxian-Yangxin fault. 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SEISMOLOGY AND EGOLOGY    0, (): 0-0.   Abstract （359）            Knowledge map    Save Related Articles | Metrics

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EARTHQUAKE SEQUENCE RELOCATION AND SEISMOGENIC STRUCTURE OF THE 2024 MS7.1 WUSHI EARTHQUAKE ON JANUARY 23, 2024, XINJIANG WANG Xue-zhu, WU Chuan-yong, LIU Jian-ming, ZANG Ke-zhi, YUAN Hai-yang, GAO Zhan, ZHANG Jin-shuo, MA Yun-xiao SEISMOLOGY AND GEOLOGY    2025, 47 (2): 488-506.   DOI: 10.3969/j.issn.0253-4967.2025.02.20240153 Abstract （347）   HTML （28）    PDF（pc） （11676KB）（117）       Knowledge map    Save At 2:09 on January 23, 2024(Beijing time), an earthquake of MS7.1 occurred in Wushi County, Aksu region, Xinjiang Uyghur Autonomous Region. This earthquake is the first earthquake with a magnitude greater than 7 in the Tian Shan seismic belt after the 1992 Susamer M7.3 earthquake. This earthquake occurred near the range-front Maidan fault which is the boundary structure between the southern Tian Shan and Tarim Basin. In fault geometry, the Maidan fault shows a complex geometry. On the plane, the Maidan fault comprises multiple roughly parallel secondary faults. On the profile, the gently dipping mountain front fault controls the folding deformation of the late Cenozoic. The front and back mountain faults converge in the deep part. This causes the Tarim Plate to deeply subduct along a large subduction zone under the Tianshan. The thrust-nappe structural system is often composed of multiple fault zones that can generate strong earthquakes because these fault zones converge to the same detachment surface in the deep part. Because a fault zone triggers or suppresses strong seismic activity in adjacent faults after a strong earthquake. Because the main earthquake did not generate obvious coseismic surface ruptures, there is still a great controversy and uncertainty on its seismogenic structure. Determination of the seismogenic structure is crucial for analyzing the potential location of the next major earthquake. It is of great significance for evaluating the future risk of strong earthquakes in the region and the stress loading and triggering relationships between different faults. According to the analysis of Google’s high-precision satellite image interpretation results and field inspections, the geometric structure of Maidan is more complicated. The fault is roughly near the ancient stream of Yu Shangu Xi River, and it can be divided into two branches, east and west of the left steps. The faults all show clear signs of activity at the surface. In this study, we utilize the earthquake relocation results to determine the seismogenic structure of the 2024 Wushi event. Our results show that the main shock began to break in the deep and the aftershocks are extended from deep to the part. The deeper focal depth may be an important factor in preventing the coseismic sliding of the Wushi MS7.1 earthquake from being transmitted to the surface. The seismic sequence is exhibited by the northeast-southwest. The long axis direction is about 55°, and the total length is about 85km. The aftershock sequence is divided into the northeast, middle section, and southwest section. The rupture range of the Wushi MS7.1 earthquake is about 35km, which is the middle section of the aftershock sequence. The aftershocks in the northeast section are mainly distributed along F1-1, the aftershocks in the southeast section are mainly distributed along F2-2 and the aftershocks in the middle section are mainly distributed along F1-2. The aftershocks of different sections are distributed on different branches, which means that the strong earthquake triggered the adjacent seismic activity, which belongs to a more complicated grade joint rupture earthquake. At the same time, the CAP waveform counter and method was adopted to obtain the focal mechanism. The nodal planes parameters of the best double-couple focal mechanisms are: strike 115°, dip 52° and rake 132° for nodal plane I, and strike 240°, dip 54° and rake 49° for nodal plane Ⅱ, the depth of the centroid is about 17km. Based on the inversion results of the focal mechanism and the spatial distribution characteristics of the earthquake sequence, we believe that nodal plane II is the seismogenic fault plane. Based on the spatial distribution characteristics of the earthquake sequence, the focal mechanism solution, and the geological structure data of the earthquake area, we suggest that the Biedieli-goukou fault is the piedmont branch of the Maidan fault. The upper part of the fault(4~5km)has no rupture, and it still has a strong risk of strong earthquakes in the future. The Wushi MS7.1 earthquake triggered the Biedieli fault and the Aheqi fault. During the Late Quaternary period, these faults have repeatedly ruptured to the surface of strong earthquake incidents. Table and Figures | Reference | Related Articles | Metrics

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PRELIMINARY STUDY ON THE SEISMOGENIC STRUCTURE OF THE 2024 M5 EARTHQUAKE SWARM IN YULI, TARIM BASIN LI Jin, DENG Ming-wen, ZHANG Zhi-guang, SUN Ye-jun, YAO Yuan, XU Kai-chi SEISMOLOGY AND GEOLOGY    2025, 47 (2): 463-487.   DOI: 10.3969/j.issn.0253-4967.2025.02.20250064 Abstract （341）   HTML （20）    PDF（pc） （9183KB）（116）       Knowledge map    Save The Tarim Basin, a typical small cratonic basin and the largest inland basin in China, is bordered by three major orogenic belts: the Kunlun, Altun, and Tianshan Mountains. Prior to 2000, seismic activity within the basin was sparse. However, with the ongoing development of oil and gas exploration and extraction after 2000, seismicity began to increase, forming a distinct pattern of earthquake swarms—referred to as the Tarim earthquake swarm. Notably, since 2017, both the frequency and magnitude of earthquakes have risen significantly. Major events include the Kuqa M5.6 earthquake on January 16, 2020, the Shaya M6.1 earthquake on January 30, 2023, and three M5.0 earthquakes in the Yuli-Kuqa area in 2024. The rising seismicity has drawn increasing attention, particularly due to heightened activity in the Yuli region since June 2024, now considered the most seismically active area in both Xinjiang and China. This study applies the Cut and Paste(CAP)method to invert focal mechanisms for three M5.0 earthquakes and other events above ML4.0 within the Yuli earthquake swarm. The double-difference relocation method was employed to refine the hypocentral locations of earthquakes above ML2.0. Furthermore, by analyzing the spatial distribution of smaller events and modeling the regional stress field, the study infers plausible parameters for seismogenic fault planes and investigates the faults responsible for the swarm. Among the 44 earthquakes analyzed, 42 exhibit strike-slip focal mechanisms. Cluster analysis reveals the presence of nearly north-south(NS)oriented nodal planes, consistent with regional strike-slip faulting trends in the NS to NNE direction. The relocated seismic sequence shows a clear division into eastern and western branches, both exhibiting linear NNE-trending patterns. Initially, seismic activity was concentrated in the eastern segment, but both branches demonstrated a northward migration over time. Based on the focal mechanisms, relocation data, and inferred fault plane parameters—combined with known fault structures in the region—it is preliminarily concluded that the Yuli earthquake swarm occurred along two nearly parallel, NNE-trending, right-lateral strike-slip faults: F1(east)and F2(west). Both faults are nearly vertical, with F1 exhibiting a steeper dip. The fault depths are estimated at 20~25km. The previously mapped faults FⅠ18 and FⅠ16 near the Yuli swarm may correspond to the shallow and deep sections of faults F1 and F2, respectively. The eastern fault(FⅠ18/F1) maintains consistent dip characteristics from shallow to deep levels, whereas the western fault(FⅠ16/F2)displays a gentler dip at depth compared to the surface. In addition to the Yuli swarm, the Tarim Basin has recently experienced the 2012 Luopu M6.0 earthquake(thrust)and the 2023 Shaya M6.1 earthquake(strike-slip), reflecting diverse faulting mechanisms driven by a common regional tectonic regime. The Luopu event resulted from thrusting of the Bachu Uplift toward the Awati Depression, induced by the ongoing convergence of the Indian and Eurasian plates. In contrast, the Shaya earthquake and the Yuli swarm likely represent secondary strike-slip structures accommodating crustal deformation from northward-directed compressive stress associated with NW- and EW-trending thrust belts in the basin interior. The Yuli earthquake swarm is located in the Yuke region of eastern Tarim, an area rich in oil and gas resources. In recent years, extraction activities have intensified, raising questions about a potential link between these activities and the increased seismicity. Further investigation is required to clarify the relationship between industrial activity and the occurrence of the Yuli earthquake swarm. Table and Figures | Reference | Related Articles | Metrics

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CHARACTERISTICS AND SEISMIC STRUCTURE ANALYSIS OF THE MS5.9 AND MS4.7 EARTHQUAKE SEQUENCES IN ALUKEERQIN BANNER, INNER MONGOLIA WANG Xin, ZHANG Ke, WANG Yue SEISMOLOGY AND GEOLOGY    2024, 46 (6): 1314-1331.   DOI: 10.3969/j.issn.0253-4967.2024.06.006 Abstract （336）   HTML （19）    PDF（pc） （7235KB）（158）       Knowledge map    Save The Alukeerqin Banner region in Chifeng city, Inner Mongolia, experienced two notable earthquakes, with magnitudes of MS5.9 and MS4.7, in 2003 and 2021, respectively. These were the most significant seismic events in the area in recent years, however, neither resulted in surface rupture. The distribution of aftershocks also did not align with known fault lines, and both the characteristics and mechanisms of these seismic activities remain unclear. To address this, we utilized data from the Inner Mongolia Seismic Monitoring Network to reposition the MS5.9 and MS4.7 earthquake sequences in Alukeerqin Banner. The results indicate that the MS5.9 and MS4.7 earthquake sequences occurred on the western and eastern sides of the Shuiquanzigou Tianshankou fault, respectively, aligning in a northwest-southeast(NW-SE)direction. The main shocks are approximately 45km apart, with focal depths of 2-12km and 8-22km for aftershocks. The main earthquakes are situated in the southeastern portion of the aftershock sequences, which also trend NW-SE. Depth-profile analysis of the aftershock zones shows relatively simple structures, with clusters oriented in a NW trend and inclined southwest(SW). The 2003 MS5.9 earthquake sequence exhibits a fault plane with a dip angle of approximately 60°, while the 2021 MS4.7 earthquake sequence has a nearly vertical fault plane. Using the CAP method and P-wave first-motion polarity analysis, we derived focal mechanism solutions and source depths for earthquakes of ML≥1.5 in the region. The focal mechanism solution indicates that the MS4.7 main shock primarily involved left-lateral strike-slip motion at a source depth of 19.9km, which closely matches the initial rupture depth of 21km obtained from relocation. Other significant earthquakes in the series similarly exhibit left-lateral strike-slip characteristics, with most developing along a NW-SE strike plane, consistent with the seismogenic fault characteristics identified in the relocated series. Previous research also shows that the main shock of the MS5.9 earthquake sequence involved left-lateral strike-slip motion, with the B-node plane orientation(NW direction)aligning with the distribution of fine-located events and the long axis of the macroscopic intensity isoseismal line. The temporal-spatial distribution and focal mechanism analyses of the MS5.9 and MS4.7 earthquake sequences suggest that their primary faults are consistent in strike and mechanical properties with the Shuiquanzi-Tianshankou Fault, trending NW but located at different positions. This confirms that the seismogenic structure of the MS5.9 earthquake is likely a left-lateral strike-slip secondary fault on the western side of the Shuiquanzi-Tianshankou Fault, trending SW. The seismogenic structure of the MS4.7 earthquake may be a concealed fault nearby with similar characteristics to the Shuiquanzi-Tianshankou Fault. We also analyzed 71 earthquakes of magnitude 2 and above in the southeastern segment of the Daxing'anling uplift since 2012, based on observation data from the China Earthquake Networks Center. Using comprehensive focal mechanism inversion, we determined the regional P-axis distribution, finding that the primary compressive stress direction in the southeastern Daxing'anling uplift is predominantly NW and nearly east-west(EW). In the vicinity of Alukeerqin Banner, the P-axis orientation is mainly EW, reflecting a relatively simple stress field. The focal mechanisms of the 2003 MS5.9 and 2021 MS4.7 earthquakes are consistent with this regional stress field, suggesting that these earthquakes were likely caused by faulting influenced by the nearly EW-oriented regional principal compressive stress. Table and Figures | Reference | Related Articles | Metrics

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SURFACE RUPTURE OF THE FEBRUARY 6, 2023 MW7.5 ELBISTAN EARTHQUAKE IN TURKEY YU Jing-xing, REN Zhi-kun, ZHANG Hui-ping, LI Chuan-you, WANG Shi-guang, GONG Zheng, ZHOU Xiao-cheng, XU Yue-ren, LIANG Peng, MA Zi-fa, LI Jun-jie SEISMOLOGY AND GEOLOGY    2024, 46 (6): 1263-1279.   DOI: 10.3969/j.issn.0253-4967.2024.06.003 Abstract （330）   HTML （40）    PDF（pc） （13905KB）（158）       Knowledge map    Save On February 6, 2023, two destructive earthquakes struck southern and central Turkey and northern and western Syria. The epicenter of the first event(MW7.8)was 37km west-northwest of Gaziantep. The earthquake had a maximum Mercalli intensity of Ⅻ around the epicenter and in Antakya. It was followed by a MW7.7 earthquake nine hours later. This earthquake was centered 95km north-northeast from the first one. There was widespread damage and tens of thousands of fatalities. In response to these catastrophic events, in March 2023, a seismic scientific expedition led by China Earthquake Administration(CEA)was promptly organized to investigate the surface ruptures caused by these earthquakes. Here, we focus on the surface ruptures of the second earthquake, known as the Elbistan earthquake. The post-earthquake field survey revealed that the Elbistan earthquake occurred on the East Anatolian fault zone's northern branch(the Cardak Fault). This event resulted in forming a main surface rupture zone approximately 140km long and a secondary fault rupture zone approximately 20km long, which is nearly perpendicular to the main rupture. We combined the interpretation of high-resolution satellite imagery and geomorphic investigations along the fault to determine the fault geometry and kinematics of the second earthquake event. The Elbistan earthquake formed a main surface rupture zone approximately 140km long, which strikes in an east-west direction along the Cardak Fault. The main rupture zone starts from Göksun in the west and extends predominantly eastward until the western end of the Sürgü Fault. It then propagates northeast along the southern segment of the Malatya fault zone. The entire Cardak Fault and the Malatya fault zone's southern segment are considered seismic structures for this earthquake. The overall surface rupture zone exhibits a linear and continuous distribution. Secondary ruptures show a combination of left-lateral strike-slip or left-lateral oblique-thrust deformation. Along the rupture zone, a series of en echelon fractures, moletracks, horizontal fault striations, and numerous displaced piercing markers, such as mountain ridges, wheat fields, terraces, fences, roads, and wheel ruts, indicate the predominance of pure left-lateral strike-slip motion for most sections. The maximum measured horizontal displacement is(7.6±0.3)m. According to the empirical relationship between the seismic moment magnitude of strike-slip faulting earthquakes and the length of surface rupture(SRL), a main rupture zone of 140km in length corresponds to a moment magnitude of approximately 7.6. Based on the relationship between the seismic moment magnitude and the maximum coseismic displacement, a maximum coseismic displacement of(7.6±0.3)m corresponds to a moment magnitude of about 7.5. The magnitudes derived from the two empirical relationships are essentially consistent, and they also agree with the moment magnitude provided by the USGS. Besides the main surface rupture zone, a secondary fault rupture zone extends nearly north-south direction for approximately 20km long. Unfortunately, due to the limited time and traffic problem, we did not visit this north-south-trending secondary fault rupture zone. According to the summary of the history of earthquakes, it is evident that the main surface rupture zone has only recorded one earthquake in history, the 1544 MS6.8 earthquake, which indicates significantly less seismic activity compared to the main East Anatolian Fault. Moreover, the “earthquake doublet” will inevitably significantly impact the stress state and seismic hazard of other faults in the region. Seismic activity in this area remain at a relatively high level for years or even decades to come. The east-west striking fault, which has not been identified on the published active fault maps at the western end of the surface rupture zone, and the north-east striking Savrun Fault, which did not rupture this time, will experience destructive earthquakes in the future. It remains unknown why the east-west striking rupture did not propagate to the Sürgü Fault this time. More detailed paleoearthquake studies are needed to identify whether it is due to insufficient energy accumulation or because this section acts as a barrier. If the Sürgü Fault, about 40km long, was to rupture entirely in the future, the magnitude could reach 7 based on the empirical relationship. Considering the distribution of historical earthquakes along the East Anatolian fault zone, as well as the geometric distribution of the surface ruptures from the recent “earthquake doublet” and the surrounding active faults, it is believed that the future earthquake hazards in the northeastern segment of the East Anatolian fault zone, the northern segment of the Dead Sea Fault, and the Malatya Fault deserve special attention. Table and Figures | Reference | Related Articles | Metrics

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THE RANGE OF DEFORMED ZONE BASED BY ACTIVE FAULT OFFSET BASED ON STATISTICAL ANALYSIS OF SURFACE RUPTURE ZONE WIDTH ZHANG Wei-heng, ZHANG Dong-sheng, CHEN Jie, TIAN Qin-jian, HE Wan-tong SEISMOLOGY AND GEOLOGY    2025, 47 (1): 345-366.   DOI: 10.3969/j.issn.0253-4967.2025.01.020 Abstract （328）   HTML （21）    PDF（pc） （7728KB）（149）       Knowledge map    Save Analyzing the statistical data on the widths of earthquake surface rupture zones is one of the most objective methods for determining the extent of active fault offsets and deformed zones. This information is crucial for establishing the setback distances for significant engineering projects in areas affected by active faults. In this study, we collected data from 92 cases to compute the widths of surface rupture zones and subsequently analyzed the extent of active fault offsets and deformed zones. Specifically, our dataset includes 75 cases with surface rupture zone widths extracted from published sources and 49 cases with available surface rupture vector data. When compiling the statistical data on surface rupture widths, we categorized the data based on whether the ruptures occurred along straight fault segments or along more geometrically complex segments. For the vector data, we normalized the distributed rupture length and primary rupture length for each case to determine the distribution proportion of the rupture zones relative to fault distance. The statistical analysis of document data shows that the total width of surface rupture zones in geometrically complex sections of normal, thrust, and strike-slip faults does not exceed 8100m, 3700m, and 10100m, respectively. In contrast, the widths of surface rupture zones in straight fault sections are generally narrower, with maximum widths of 160m, 120m, and 400m for normal, thrust, and strike-slip faults, respectively. The vector data further reveal that the maximum distances between the distributed ruptures and the primary fault are as follows: 19212m for the hanging wall of normal faults, 16244m for the footwall of normal faults, 7579m for the hanging wall of thrust faults, 4216m for the footwall of thrust faults, and 120456m for strike-slip faults. Moreover, the maximum distances from the primary fault to the margin of the closely distributed rupture zones are 700m, 200m, 1000m, 400m, and 500m, respectively. It is important to note that when excluding exceptional cases, such as earthquakes associated with fold-related faults or gently dipping thrust faults, the maximum distance from the margin of the closely distributed rupture zone to the primary fault is as follows: 400m for the hanging wall of normal faults, 200m for the footwall of normal faults, 500m for the hanging wall of thrust faults, 200m for the footwall of thrust faults, and 400m for strike-slip faults. Based on this comprehensive analysis, we suggest that the range of active fault offset and deformed zones should be considered as 400~500m from the primary fault. However, further research is needed to accurately determine the extent of fault offsets and deformed zones in areas with complex structural features, such as fault bends, step zones, fault tails, and the hanging walls of foreland thrust faults. Future studies would benefit from incorporating more extensive and detailed surface rupture data. Continued data collection is essential to improve the accuracy and robustness of the results. Table and Figures | Reference | Related Articles | Metrics

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GROWING HISTORY AND GEOMORPHIC RESPONSE OF THE EASTERN TERMINATION OF KASHI ANTICLINE, SOUTHWESTERN TIAN SHAN: AN INTEGRATED ANALYSIS OF GEOLOGY, GEOMORPHOLOGY, SEISMIC REFLECTION PROFILE AND MAGNETOSTRATIGRAPHY HE Peng-yu, LI Tao, CHEN Zhu-xin, CHEN Jie SEISMOLOGY AND GEOLOGY    2025, 47 (2): 369-383.   DOI: 10.3969/j.issn.0253-4967.2025.02.20240157 Abstract （327）   HTML （27）    PDF（pc） （7786KB）（165）       Knowledge map    Save The Kashi anticline, located along the leading edge of the Kashi foreland thrust system in the southwestern Tian Shan of China, confronts the Atushi Anticline to the north and connects with the Mingyaole Anticline to the west. The Kashi anticline manifests at the surface as an elongated hillock with a nearly EW strike. The morphology of the anticline is roughly box-shaped, with the southern limb being gentler compared to the northern limb. As a significant component of the Tianshan orogenic belt’s frontal zone, the study of the tectonic evolution of the Kashi Anticline is crucial for understanding the Cenozoic tectonic deformation and crustal shortening processes of the Tian Shan. Previous studies on this fold are primarily focused on its surface-expression part, with little or no focus on its lateral termination that is not expressed on the land surface, which has limited the comprehensive understanding of the anticline’s overall evolutionary process. The study employs the depth-relief area method, combined with high-resolution seismic reflection profile data, to conduct a detailed structural analysis of the eastern termination of the Kashi anticline. Through meticulous interpretation and quantitative analysis of the seismic profiles, the following key insights have been obtained: Firstly, along the seismic profile, the Cenozoic strata are approximately 6.8km thick, while the Mesozoic-Paleozoic strata are about 2.2km thick. The eastern termination of the anticline detaches along the Paleogene unit, with a depth of ~6.8km. This detachment layer governs the deformation patterns and magnitudes of the overlying strata. Secondly, along the seismic profile, the total shortening of the anticline is estimated to be(882±79)m, of which approximately 94% is attributed to shear shortening, and about 6% is due to curvietric shortening. During the folding process, materials with an excess area of ~3.4km2 enter the cross section. Thirdly, according to the analysis of growth strata and published magnetostratigraphic data, the folding of the eastern termination initiates at the age of ~2.1Ma, which implies that the initiation age of the fold should be much older than 2.1Ma. The shortening rate remains at an approximate constant of ~0.4mm/a since the folding initiation. Fourthly, for the pre-growth strata, the uplift of the anticline gradually increases upward with depth, reaching a maximum of approximately 770m at the top boundary of the pre-growth strata. Analysis of the growth strata indicates that the uplift rate either keeps a constant of ~0.4mm/a, or increases significantly from an earlier rate of ~0.1mm/a to a later rate of 0.4 mm/a at the age point of ~1.6Ma. Notably, because the uplift rate is smaller than the sediment rate, the fold exhibits no expression on the surface of the anticline. Our study exemplifies that an analysis of the buried lateral termination of a fold can well determine the detachment level, shortening and uplift histories, initiation age of the fold, as well as whether or not the excess area enters the cross section during the folding process. These constraints provide a completer and more reliable basis for understanding the entire growing history of the fold. Furthermore, the results demonstrate that the analysis of buried structures in the frontal zones of orogenic belts is indispensable for a comprehensive understanding of regional tectonic deformation characteristics and evolutionary history. Table and Figures | Reference | Related Articles | Metrics

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INSAR COSEISMIC DEFORMATION AND SEISMOGENIC STRUCTURE OF THE 2024 MW7.0 WUSHI EARTHQUAKE CHEN Zi-long, LIU Gang, LI Qi, CHEN Wei, ZHAO Xin-yu, LIN Mu, TAO Long-wen, QIAO Xue-jun, NIE Zhao-sheng SEISMOLOGY AND GEOLOGY    2025, 47 (2): 429-447.   DOI: 10.3969/j.issn.0253-4967.2025.02.20240142 Abstract （324）   HTML （26）    PDF（pc） （11046KB）（136）       Knowledge map    Save On January 30, 2024, an MW7.0 earthquake struck the Wushi region of the southern Tianshan Mountains, Xinjiang, China. This earthquake, located in a tectonically active zone dominated by intense crustal shortening and thrust faulting, providing a valuable opportunity to investigate fault geometry and rupture mechanisms in the region. We utilized Sentinel-1 InSAR data combined with advanced inversion techniques to analyze the coseismic deformation field, determine fault parameters, and explore the spatial relationship between the mainshock and aftershocks. High-resolution coseismic deformation fields were generated using D-InSAR processing of Sentinel-1A ascending and descending orbit data. Nonlinear inversion methods were employed to calculate fault geometry and sliding distribution, with both single-fault and dual-fault models tested to accommodate the complex faulting characteristics. Residual analysis was performed to examine the relationship between the mainshock and the MW5.7 aftershock, and geological surveys were used to validate fault models and rupture characteristics. The maximum line-of-sight(LOS)displacement of the coseismic deformation field reached 70cm, displaying an elliptical pattern along the Maidan Fault. The dual-fault model revealed significant geometric complexity: the fault strike rotates clockwise by 20°~25° east of the epicenter, and the dip angle decreases from 60° in the west to 40° in the east. Fault slip was primarily concentrated west of the epicenter, characterized by high-angle thrusting with a left-lateral component, while slip in the eastern segment was lower in magnitude and relatively dispersed. The overall distribution exhibited shallow slip deficit. The correlation between geometric variations and sliding distribution suggests the presence of a geometric barrier east of the epicenter, acting as an obstacle to rupture propagation. The coseismic rupture was confined between the Yushanguxi River and the Wushi depression, with fault steps and structural complexities on the eastern and western boundaries limiting the rupture extent. The MW5.7 aftershock produced a clear LOS deformation field, with the fault strike deviating by ~10° from the mainshock trace and dipping southeast. The surface trace of the aftershock fault closely aligned with mapped surface ruptures, and the shallow slip magnitude matched the observed vertical offsets from geological surveys. We also demonstrates that fault geometry plays a significant role in controlling rupture propagation and termination. The geometric barrier east of the epicenter effectively limited eastward rupture propagation, while a wide fault step near the Yushanguxi River constrained the western rupture. The Wushi earthquake was identified as a blind rupture event, with no significant primary surface rupture. The distribution of secondary geological hazards aligned well with fault slip characteristics, and the spatial relationship between aftershock slip and the mainshock highlights fault segmentation within the Ush thrust belt. Table and Figures | Reference | Related Articles | Metrics

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STUDY ON FAULT DEFORMATION CHARACTERISTICS AND SEISMIC HAZARD IN THE KEPING THRUST BELT ZHU Shuang, GUO Nan-nan, PANG Ya-jin SEISMOLOGY AND GEOLOGY    2025, 47 (2): 448-462.   DOI: 10.3969/j.issn.0253-4967.2025.02.20240147 Abstract （323）   HTML （14）    PDF（pc） （6489KB）（82）       Knowledge map    Save As one of the most seismically active regions in China, the southwestern Tianshan exhibits the necessary tectonic conditions and energy accumulation for earthquakes exceeding magnitude 6. Investigating the region's tectonic deformation characteristics is crucial for understanding the background of strong earthquakes and assessing future seismic hazards. In this study, we compiled and analyzed multi-period GNSS velocity fields from domestic and international sources, generating a fused velocity field. The results indicate that the crustal deformation of the Tianshan seismic belt is spatially heterogeneous, influenced by the combined effects of the clockwise rotation of the Tarim Basin and the northward thrust of the Pamir Plateau. Additionally, three north-south profiles across the study area were analyzed. The western Tianshan(Profile 1)exhibits a higher north-south compression rate, which gradually decreases eastward, consistent with the velocity field trends. Using the fused GNSS velocity field, we calculated the strain rate field through the least-squares collocation method, obtaining strain characteristics of the Keping thrust belt and surrounding areas. The Piqiang fault zone serves as a boundary, with compressive strain on the western side of the Keping thrust belt exceeding that on the eastern side. The average surface strain rate is -3.3×10-8/a in the west and -1.2×10-8/a in the east. Similarly, the maximum shear strain follows this pattern, with values of 2.7×10-8/a in the west and 1.1×10-8/a in the east, indicating distinct deformation characteristics on either side of the Keping thrust belt. Focal mechanism solutions of earthquakes(M≥4.0)since 1976 were collected, and stress inversion analysis was conducted at various depths. Earthquakes in the Tianshan region predominantly occur within the upper 50km of the crust. The results reveal a nearly north-south principal compressive stress orientation, perpendicular to the Tianshan orogenic belt, aligning with the regional surface principal compressive strain rate. However, due to the presence of conjugate strike-slip faults and strike-slip earthquakes in the northern and southern Tianshan hinterland, local horizontal principal stress directions deviate from the regional trend. Integrating InSAR-derived deformation data with GNSS velocity field results, we calculated fault slip deficit rates and slip rates for major faults in the Keping thrust belt using a three-dimensional block model. The western Keping fault zone exhibits a higher compression rate of(3.1±0.3)mm/a, whereas the eastern section has a lower rate of(0.3±0.2)mm/a. The Maidan fault's western section has a compression rate of(2.7±0.5)mm/a, increasing to(3.7±0.4)mm/a in the east. Additionally, the left-lateral strike-slip rate is higher in the western Keping fault zone((1.5±0.3)mm/a)compared to the eastern section((0.5±0.2)mm/a). The Maidan fault follows a similar pattern, with strike-slip rates of(0.9±0.5)mm/a in the west and(2.1±0.4)mm/a in the east. The slip deficit rate distribution indicates high values in the western Keping fault zone, corresponding to the Jiashi earthquake swarm, while the eastern section exhibits lower deficit and slip rates, potentially due to a multilayer nappe structure. In the Maidan fault zone, the western section has a lower slip deficit and slip rate, suggesting weak crustal strength and limited stress accumulation, whereas the eastern section has higher values, correlating with the Wushi earthquake and subsequent energy release. Finally, based on the calculated strain field and the global focal mechanism earthquake catalog(1976—2021), we applied the SHIFT_GSRM2f model developed by Bird et al. to predict shallow earthquakes. The highest predicted seismic hazard values are concentrated in the southwestern Tianshan, particularly in the Pamir region, which has a higher risk of strong earthquakes than the Keping thrust belt. However, the Keping thrust belt remains one of the most seismically hazardous areas in the Tianshan region, underscoring the continued seismic risk in southwestern Tianshan. Table and Figures | Reference | Related Articles | Metrics

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HIGH-RESOLUTION S-WAVE VELOCITY STRUCTURE OF BEIJING AREA USING AMBIENT NOISE TOMOGRAPHY JI Yu, ZHANG Guang-wei, REN Jun-jie, HE Jing, WANG Xiao-wei SEISMOLOGY AND GEOLOGY    2025, 47 (1): 306-324.   DOI: 10.3969/j.issn.0253-4967.2025.01.018 Abstract （319）   HTML （14）    PDF（pc） （14562KB）（110）       Knowledge map    Save Beijing is located at the intersection of the Yanshan Mountains, Taihang Mountains, and the northwestern part of the North China Basin. This region has experienced multiple periods of crustal movement, forming a series of Cenozoic Basins exhibiting alternating uplifts and depressions. The intense tectonic activity has resulted in a relatively complex fault system, with the main directions of the faults being NE and NW. Notably, the Xixiadian Fault in the NE direction experienced an earthquake with a magnitude of 8 in 1679. Meanwhile, the NW-oriented Nankou-Sunhe Fault offsets multiple NE-oriented faults and directly passes through urban residential areas, making it an important active fault in Beijing. Although these intersecting faults have not experienced earthquakes of magnitude 4 or higher in recent decades, small seismic events(M<4.0)still occur frequently. Furthermore, the thickness of Quaternary sedimentary layers in the Beijing area varies significantly. These relatively low-velocity sedimentary layers can cause seismic site effects such as amplitude amplification of seismic waves and increased vibration duration. Therefore, disaster detailed study of the three-dimensional velocity structure of the upper crust and depression areas in Beijing is of great significance for analyzing potential disasters and assessing seismic hazards. This study utilized continuous waveform data from 28 permanent seismic stations. The stations are distributed across the Beijing area, with an average inter-station distance of approximately 30km. This study's continuous constant waveform data spans from April 2022 to October 2022. For the Nankou-Sunhe Fault in the Changping area, we employed 109 short-period temporary seismic stations located around the fault zone. The seismic data is recorded from July 2, 2022, to August 3, 2022, over 33 days, with an average inter-station distance of approximately 2km. By applying the ambient noise tomography method, we successfully inverted the three-dimensional S-wave velocity structures of the upper crust for the Beijing region and the near-surface for the Nankou-Sunhe fault zone. Our results reveal that the velocity structure beneath the Beijing area exhibits significant lateral heterogeneity. The Yanshan uplift in the north, the Jingxi uplift in the west, and the Daxing uplift in the southeastern part of the study area present obvious high-velocity anomalies, reflecting a relatively dense crystalline basement. In the Dachang depression and Shunyi depression areas, the structures from shallow to 7km depth show characteristics of low-velocity anomalies, indicating a relatively deep sedimentary layer in this area. Meanwhile, the distribution of low-velocity anomalies within the study area mainly presents a NE direction, consistent with the dominant strike direction of fault zones. Based on the results of small-scale dense seismic array inversion, it shows that the dip angle of the Nankou-Sunhe Fault is quite steep, controlling the northern boundary of the Shahe depression, and the sedimentary thickness of the Shahe depression is much deeper than that of the Shangzhuang depression. Overall, the significant low-velocity anomaly in the depression reflects the direction of the fault controls the deep sedimentary layer, and the boundary of the depression. The velocity structure in the uplift area shows a high-velocity anomaly, which reflects the relatively old rock stratum. Additionally, the inversion results based on a small-scale dense array reveal that the fault plane of the Nankou-Sunhe Fault is relatively steep, which controls the northern boundary of the Shahe depression. The thickness of the sedimentary layer in the Shahe Depression varies significantly along the fault strike, and the deepest layer is up to 1.5km, which is much deeper than that of the Shangzhuang Depression. Furthermore, the detailed three-dimensional velocity structure model in this study provides direct seismological evidence for the existence of the Dongbeiwang-Xiaotangshan buried fault in Beijing. In summary, this study shows that seismic tomography using urban ambient noise can efficiently and economically obtain the three-dimensional velocity structure, as well as has broad prospects in identifying geological structural units and hidden faults. Table and Figures | Reference | Related Articles | Metrics

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CURRENT TECTONIC ACTIVITY OF THE CANGSHAN-NISHAN FAULT AND ITS IMPACT ON THE RESIDENTIAL BUILDING DAMAGE WANG Yi-ying, SUN Xi-xi, ZHU Meng, WANG Ji-qiang, SHI Pi-long, WANG Hua-lin SEISMOLOGY AND GEOLOGY    2024, 46 (6): 1426-1443.   DOI: 10.3969/j.issn.0253-4967.2024.06.012 Abstract （309）   HTML （18）    PDF（pc） （12473KB）（98）       Knowledge map    Save The NW-trending Cangshan-Nishan(Cang-Ni) Fault, extending 170km, exhibits significant tectonic deformation and seismic activity in the late Quaternary, attracting considerable attention. This study investigates the relationship between residential building damage in Guanzhuang village, Baiyan town, Pingyi county, Shandong Province, and the activity of the Cang-Ni Fault. Based on field investigations, geomorphological measurements, fault activity identification, surface structure analysis of quartz fragments in fault gouge(SEM), particle size distribution analysis, InSAR time-series analysis, historical research on the 179BC M7 Qichu earthquake, and previous earthquake damage studies, the following conclusions were drawn: 1)Severe structural damage with left-lateral displacement of 0.5-2cm was observed in buildings along the main Cang-Ni Fault, with cracks originating at foundations and decreasing in scale upward. In contrast, buildings along secondary faults experienced relatively minor damage. Foundation cracks in the main fault zone were wide and numerous, propagating upwards to narrower wall fissures, indicative of structural failure. 2)Damaged buildings in Guanzhuang village align with the left-lateral strike-slip zone of the Cang-Ni Fault, coinciding with the epicenter of the 179BC M7 Qichu earthquake. This area represents the hub of late Quaternary fault activity, characterized by significant displacement and recent faulting strata. 3)SEM analysis of quartz fragments suggests that the Cang-Ni Fault's latest activity occurred in the early Holocene, with a combination of stick-slip and creep-slip mechanisms. Particle size analysis revealed a high proportion(36%-43%)of ultra-fine particles(<0.001mm)and fractal dimension values of 2.817-2.857, favoring fault creep. 4)InSAR data confirm ongoing sinistral strike-slip movement of the Cang-Ni Fault, indicating surface creep deformation. 5)Damage to residential buildings is attributed to the sinistral strike-slip and reverse-thrust creep deformation of the fault, stratigraphic and structural differences across fault walls, uneven stress distribution, and swelling effects of fault gouge. This research provides a case study of building damage caused by active fault creep, emphasizing the importance of precise identification and spatial mapping of active faults for seismic design and site selection in engineering projects. The findings offer valuable insights for mitigating seismic hazards in fault zones. Table and Figures | Reference | Related Articles | Metrics

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EARTHQUAKE CASUALTY RISK ANALYSIS UNDER THE RECURRENCE SCENARIO OF THE 1902 ARTUX MS8¼ EARTHQUAKE: A CASE STUDY OF KASHGAR AND ARTUX NIE Wen-yu, FAN Xi-wei, LI Hua-yue, QI Yuan-meng, LIU Min SEISMOLOGY AND GEOLOGY    2025, 47 (2): 627-648.   DOI: 10.3969/j.issn.0253-4967.2025.02.20240156 Abstract （298）   HTML （19）    PDF（pc） （16445KB）（47）       Knowledge map    Save Despite global efforts to reduce earthquake disaster risk, earthquakes remain one of the most destructive natural disasters in the world. Since precise earthquake prediction remains beyond human capability, conducting accurate earthquake casualty risk assessment has become one of the most feasible and effective strategies to reduce human losses. Kashgar and Artux are located in the southwestern part of the Xinjiang Uygur Autonomous Region, on the western edge of the Tarim Basin. These are two important cities in northwest China, situated in the Pamir tectonic knot region of the India-Eurasia continental collision zone, one of the world’s most seismically active regions due to intracontinental subduction. Historically, this region has experienced multiple major earthquakes, with the most representative example being the 1902 Artux earthquake, which had a magnitude of MS8¼. This earthquake caused severe casualties and highlighted the region’s high susceptibility to seismic hazards. In this study, we used the historical seismic intensity scenario of the 1902 Artux earthquake as a deterministic earthquake scenario to understand the potential impact of a similar event under contemporary conditions. First, using time-series mobile signaling data and machine learning methods, we extracted the function types of buildings in the study area and developed a thematic dataset of building function types. Utilizing the extracted building function types, high-resolution population heatmap data, and a mapping method between grids and individual buildings, we allocated the population within the grids to specific buildings. Subsequently, by considering the relationships among building function types, temporal characteristics, local daily activity patterns, and indoor occupancy rates, we determined the spatial distribution of the indoor population in the study area. Understanding the potential damage levels of buildings under specific seismic scenarios is crucial for predicting casualty risks and formulating effective emergency response strategies. Therefore, a quantitative analysis of building damage levels under the deterministic earthquake scenario was conducted to clarify damage distribution for buildings in specific intensity scenarios. Subsequently, based on building vulnerability analysis methods, we estimated the daytime and nighttime fatality risks under the recurrence of the Artux earthquake at a 30″grid scale. The results indicate that if the 1902 MS8¼ Artux earthquake were to recur, areas with high risk of fatalities would mainly be concentrated in the densely populated urban centers of Kashgar and Artux, where buildings are densely packed, populations are concentrated, and some structures lack adequate seismic resistance. The risk of casualties is higher at night than during the daytime. To evaluate the effectiveness of population heatmap data in earthquake casualty assessment, this study compared the evaluation method based on population heatmap data with the method using the Seventh National Census data. The results demonstrate that traditional census data can only provide a rough estimate of casualties based on administrative divisions. However, its reliance on administrative boundaries means it lacks the spatial detail necessary to accurately depict casualty distribution and presents scale inconsistencies that hinder effective risk comparisons across different areas. In contrast, the assessment method based on population heatmap data enables spatial visualization of fatality risks through optimized scaling and establishes a uniform spatial comparison benchmark, thereby providing strong support for the precise allocation of emergency rescue resources. By introducing high-resolution population heatmap data and a thematic dataset of building function types, this study has enhanced the accuracy and practicality of earthquake casualty risk assessment. The results not only reveal the potential for high human casualties if a historical earthquake were to recur today but also demonstrate the distribution characteristics and temporal differences in high-risk zones, emphasizing the importance of considering temporal factors in disaster mitigation strategies. These insights provide robust scientific support for developing precise disaster mitigation and preparedness strategies in earthquake-prone urban areas. Table and Figures | Reference | Related Articles | Metrics

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CHARACTERISTICS OF SEISMICITY AND TECTONIC STRESS FIELD IN THE NORTHEASTERN REGION OF THE PAMIR PLATEAU CUI Hua-wei, YIN Xin-zhong, CHEN Jiu-hui, GUO Biao, LI Tao, YAO Yuan, LI Shi-ying, JIA Zhen SEISMOLOGY AND GEOLOGY    2025, 47 (2): 577-596.   DOI: 10.3969/j.issn.0253-4967.2025.02.20250047 Abstract （293）   HTML （15）    PDF（pc） （15713KB）（78）       Knowledge map    Save The northeastern region of the Pamir Plateau marks the convergence of the Pamir Plateau, the Tianshan Mountains, and the Tarim Basin. This area is associated with high levels of seismic activity and has experienced significant casualties due to several major earthquakes. In this study, earthquakes are relocated using the double-difference relocation algorithm, based on seismic observation reports from the China Earthquake Networks Centre(CENC)covering the period from 2008 to 2023. A total of 916 earthquake focal mechanisms were collected from various institutions and studies, including the GCMT, WWSSN, previous research, and the Xinjiang Earthquake Agency. The magnitudes of these events range from M2.8 to M8.2, and the time span extends from 1902 to 2024. The tectonic stress field was inverted using a spatial-temporal stress inversion algorithm with a 1.0°×1.0° grid, based on these historical focal mechanisms. The relocated earthquakes are distributed along major tectonic zones situated between the Pamir Plateau, the Tianshan Mountains, and the Tarim Basin, forming several seismic clusters within the study area. Most events have focal depths of less than 30km. Seven cross-sectional profiles were selected to analyze the spatial distribution of seismicity. The regional tectonic stress field is primarily dominated by strike-slip and reverse faulting regimes. The maximum principal stress axes are compressional in a nearly horizontal south-north(S-N)direction, while the minimum principal stress axes are extensional in the east-west(E-W)direction, with either horizontal or vertical plunges. Based on the spatial distribution of seismicity and tectonic features, the study area is divided into several subregions: the central Pamir Plateau and its eastern and western flanks; the collision zone between the Pamir Plateau and the Tianshan Mountains and its surrounding areas; the Tianshan Mountains; and the interior of the Tarim Basin. Preliminary results of earthquake relocation show that focal depths in the southeastern and northwestern parts of the Qimugen Arc Tectonic Belt are deeper than those within the belt. This is attributed to the subduction of the eastern and northeastern Pamir beneath the Tarim Basin toward the east and northeast. Accordingly, the Moho depth is also greater in these regions. These observations suggest that the Qimugen Arc Tectonic Belt represents a key tectonic boundary, with both the Moho and earthquake depths shallower within the belt than in its southeastern and northwestern margins. Focal depths along the southern margin of the Tianshan Mountains are deeper than those in the adjacent Tarim Basin, which is consistent with a deeper Moho in the former. Similarly, both the Moho and earthquake depths within the Ferghana fault and Piqiang fault zones are greater than those outside these faults along the southern margin of the Tianshan Mountains, indicating that these faults serve as significant tectonic boundaries. An area of sparse seismicity overlaps with the source region of the 1902 Atushi(Kashgar)MW7.7 earthquake, suggesting that accumulated crustal stress was likely fully released by this event. Seismicity in the Tarim Basin primarily consists of aftershock sequences from the 1996-1999 earthquake clusters and the 2003 Bachu-Jiashi MS6.8 earthquake. The main contributing factors to seismicity in the Tarim Basin are thought to be its low seismic wave velocity, low crustal density, and brittle crustal properties. The initial results of the tectonic stress inversion indicate that the central Pamir Plateau is undergoing east-west lateral extension under a strike-slip stress regime, driven by compression from the Indian Plate to the south and obstruction from the Tianshan Mountains to the north. A normal faulting regime in the central grid of the Pamir Plateau is interpreted as a center of expansion or gravitational collapse. The tectonic stress field exhibits significant variation across the flanks of the Pamir Plateau. The R-value, stress regime, and plunge of the maximum principal extension axes show gradual and, in some areas, abrupt changes from the central region to the western and eastern margins, as well as in the collision zones between the Pamir Plateau and the Tianshan Mountains. The Tianshan Mountains continue to uplift due to near S-N compression, displaying a dominant reverse faulting regime. In the Bachu uplift and depression region in the southwestern Tarim Basin, the stress field is characterized by both reverse and strike-slip regimes, likely resulting from differences in crustal velocity, density, and structural composition. Table and Figures | Reference | Related Articles | Metrics

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COSEISMIC SLIP AND COULOMB STRESS OF THE 2024 MW7.1 HYUGANADA EARTHQUAKE YANG Si-yuan, HU Yan SEISMOLOGY AND GEOLOGY    2025, 47 (2): 597-609.   DOI: 10.3969/j.issn.0253-4967.2025.02.20240152 Abstract （290）   HTML （15）    PDF（pc） （4237KB）（52）       Knowledge map    Save In Southwest Japan, the Philippine Sea Plate subducts beneath the Eurasian Plate, which makes it one of the most seismically active areas in the world. This area nucleates primarily thrust-type earthquakes over the subduction interface. On August 8, 2024, a MW 7.1 earthquake occurred in the Hyuganada region in southwestern Japan, offering a valuable opportunity to investigate the seismic slip of this event. Understanding the seismic slip plays an essential role in evaluating earthquake hazards, because it helps better understand the fault behaviors and stress interactions among active crustal faults and thus potential seismic impacts. In this study, we first derived the coseismic displacements caused by the earthquake through Global Navigation Satellite System(GNSS)data. The maximum horizontal displacement is approximately 15cm, decreasing rapidly as the distance from the rupture zone increases. The vertical displacement shows distinct spatial characteristics. In the southeastern area of the Kyushu Island, near the rupture zone, the subsidence is predominant, with a maximum subsidence of about 6cm. Northwest of this area, the displacement gradually changes to uplift. This result indicates a complex deformation from the rupture area to the farther areas. Based on the elastic half-space model, we inverted the coseismic slip distribution using the derived GNSS displacements. In the model, we have considered a rupture fault with a length of 100km and a width of 60km. This fault is divided into 220 small rectangular elements, with 20 elements in the length direction and 11 in the depth direction. The length of each small rectangular tile is fixed at 5km, while the tile width varies with the depth. The minimum width is 5.2km, and the width increases with depth according to a proportionality coefficient of 1.01. We further use the grid search method to determine the fault dip angle and strike direction. The dip angle and strike direction of the fault are varied within ranges of -50° to 100° and 100° to 300°, respectively. Through these processes, the optimal fault dip angle and strike direction are determined to be 24° and 206°, respectively, consistent with the focal mechanism by the United States Geological Survey(USGS). The inverted coseismic slip distribution shows that the slip is primarily concentrated at 5~20km depths, featuring an elliptical pattern with a maximum slip of 1.47m. Based on the inverted fault slip model, we calculated the surface displacement using Okada’s half-space elastic dislocation theory. The results show that the model reproduces the first-order pattern of GNSS observations in both the horizontal and vertical directions. The total released moment is about 5.49×1019 Nm, corresponding to a moment magnitude of 7.09(assuming a shear modulus of 30GPa), which is close to the USGS of MW7.1. We calculated the Coulomb stress over the main fault using the inverted coseismic slip model. During this process, we assumed that the frictional coefficient of the fault, shear modulus, and Poisson’s ratio are to be 0.4, 30GPa, and 0.25, respectively. The fault plane’s strike, dip, and slip angles are set to be 206°, 24°, and 76°, respectively. The results reveal that outside the rupture zone, the Coulomb stress is positive, with a peak value of approximately 0.95MPa. In contrast, the overall stress is negative within the rupture zone, especially at depths between 7km and 17.5km, where it reaches a maximum value of -2.03MPa. Furthermore, the analyses on normal and shear stresses reveal a distinct pattern. In the shallow portion of the coseismic rupture zone, spanning from 0km to 7km, the normal stress is positive, with its maximum value reaching approximately 0.30MPa, whereas the shear stress is negative, peaking at around 0.73MPa. In other regions over the fault, the normal and shear stresses exhibit an increasing or decreasing trend. In addition, we have also investigated the aftershocks that occurred within one month after the earthquake, using data from the USGS and JMA(Japan Meteorological Agency). The location of these aftershocks features a depth range of 10~60km. To further investigate the mechanisms of the aftershock occurrence, we analyzed the distribution of maximum shear stress at a depth of 40km. The results show that aftershocks mainly occur in areas where the shear stress is more than 100kPa. The majority of aftershocks concentrate in areas with the shear stress larger than 500kPa. This suggests at least hundreds of kPa are required to induce aftershocks of this event To summarize, we have derived the coseismic slip and induced Coulomb stress of the 2024 Hyuganada earthquake. This reveals the seismic slip characteristics as well as impacts on the stress states and aftershock activities, which may contribute to further earthquake hazard assessment and mitigation strategies in the region. Table and Figures | Reference | Related Articles | Metrics

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GEOLOGICAL HAZARD CHARACTERISTICS AND MACRO-SCOPIC EPICENTER OF WUSHI MS7.1 EARTHQUAKE ON JANUARY 23, 2024, XINJIANG CHEN Jian-bo, ZHENG Li-ming, LI Tao, CHEN Jie, YAO Yuan, QIAN Li, ZHANG Bo-xuan, HU Zong-kai, LIU Guan-shen, LI Jin SEISMOLOGY AND GEOLOGY    2025, 47 (2): 561-576.   DOI: 10.3969/j.issn.0253-4967.2025.02.20240066 Abstract （290）   HTML （19）    PDF（pc） （14230KB）（97）       Knowledge map    Save The Wushi MS7.1 earthquake is the largest seismic event in Xinjiang in the past decade and the most significant earthquake in the Tianshan seismic belt since the Suusamyr MS7.3 earthquake in Kyrgyzstan in 1992. The microseismic epicenter is located at the transition between the Keping nappe structure belt and the Kuqa nappe belt in the southwestern Tianshan Mountains, near the intersection of the southern Tianshan Mountains and the Wushi Depression. This region is a compressional fault depression valley formed in the context of Tianshan orogeny. The northern boundary of the valley is controlled by the Maidan reverse fault zone, while multiple rows of newly developed linear uplifts and piedmont fault scarps in the northern depression are governed by low-angle overthrust and recoil faults. Focal mechanism analysis indicates that both the main shock and aftershocks exhibit a compressional thrust-type mechanism, consistent with the structural characteristics of the Wushishan front depression. Post-earthquake investigations revealed relatively minor casualties and structural damage, but secondary geological disasters were severe. Using field surveys, large-scale satellite image analysis, and drone aerial photography conducted immediately after the earthquake, this study investigates the spatial distribution, types, and development characteristics of seismic-induced geological hazards in various gullies within the affected region. Although no large-scale surface ruptures were observed at or near the epicenter, extensive seismic geological hazards were identified, providing crucial insights for determining the macroseismic epicenter and assessing the post-disaster intensity and loss in the earthquake area. Geological hazards induced by the Wushi earthquake were primarily concentrated in Biediligou, Qialematigou, Cocriu Musugou, and adjacent mountainous areas within the VII-degree seismic intensity zone. The most severe damage occurred in the Biediligou-Qialematigou region, where the macroseismic epicenter was located, with diverse types of secondary disasters, including rockfalls, landslides, rolling stones, bank slope collapses, subgrade settlement cracks, and ground fissures. Some ground fissures were accompanied by displacement. Seismic geological hazards were predominantly observed near the microseismic epicenter and within 10km of the north and south sides of the fault zone, with collapses being the most prominent, followed by pavement cracking and riverbank slope failures caused by ground fissures and uneven subgrade settlement. Post-earthquake investigations also identified numerous concentrated surface tension and shear cracks in the macroseismic epicenter, alongside earthquake-induced collapses, landslides, slope instabilities, subgrade settlements, and structural failures. Coseismic InSAR deformation field and image offset analysis revealed a maximum line-of-sight displacement of approximately 40cm and a minimum displacement of -16cm. The long axis of the deformation zone trends NE, with its strongest deformation occurring between Biediligou and Qialamatigou. This spatial distribution aligns well with the observed ground fissures and seismic deformation zones near the macroseismic epicenter, indicating that structural deformation plays a critical role in controlling the formation of earthquake-induced geological hazards. Table and Figures | Reference | Related Articles | Metrics

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GROUND MOTION SIMULATION CONSIDERING VELOCITY DISPERSION AND ITS IMPLICATIONS FOR SEISMIC HAZARD ASSESSMENT ZHANG Yan, JI Zhi-wei, ZHAI Hong-yu, WU Chun-hao SEISMOLOGY AND GEOLOGY    2024, 46 (6): 1408-1425.   DOI: 10.3969/j.issn.0253-4967.2024.06.011 Abstract （287）   HTML （14）    PDF（pc） （6993KB）（97）       Knowledge map    Save Seismic hazard assessment is crucial for determining engineering fortification levels, guiding urban planning, mitigating earthquake disasters, and addressing secondary hazards such as landslides and mudslides triggered by earthquakes. Energy attenuation during seismic wave propagation is influenced by multi-angle scattering, physical dispersion, and geometric spreading. When conducting numerical simulations of post-earthquake ground motion, accounting for these factors significantly affects the accuracy of hazard assessments. This paper examines the physical dispersion characteristics of seismic waves in viscoelastic media. Through simulations of velocity dispersion and seismic wave time distribution in a simple one-dimensional model, we explore the impact of dispersion on the spatial distribution of seismic motion and its implications for seismic hazard assessment. A case study of the 2021 Yangbi MS6.4 earthquake further illustrates the importance of considering physical dispersion in seismic hazard analysis. In contrast to traditional ground motion prediction equations(GMPE), physics-based simulations of ground motion provide more reliable estimates of seismic hazard levels and enhance the accuracy of hazard assessments. It is well-established that, excluding site effects, peak ground motion parameters on bedrock decrease with increasing epicentral distance. However, considering the wave field dispersion characteristics reveals that peak ground motion parameters do not always decrease monotonically with distance; in some cases, they may even slightly increase. This highlights the complexity of seismic wave propagation through viscoelastic media. Further validation of these findings through refined, scenario-based numerical simulations is necessary. Additionally, with increasing epicentral distance, the amplitude of ground motion time histories decreases, while their duration increases. This low-frequency, long-duration seismic motion may be amplified under specific site conditions, such as in basins. The influence of the non-uniform viscoelastic medium results in varying attenuation rates for horizontal peak ground motion parameters at different angles. The findings of this study have important implications for national security, critical infrastructure, unconventional energy development, and secondary hazards such as landslides and mudslides. The integration of source physics, seismic wave theory, medium structure imaging, and structural stress analysis is essential for improving the accuracy and reliability of seismic hazard assessments. Table and Figures | Reference | Related Articles | Metrics

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THE CHARACTERISTICS OF TERRESTRIAL TIME-VARYING GRAVITY CHANGES AND EQUIVALENT SOURCE INVERSION ON THE SOUTHEASTERN MARGIN OF THE TIBETAN PLATEAU ZHENG Qiu-yue, CHEN Zheng-yu, WU Yu-qin, HUANG Jiang-pei, LIU Dong, WANG Qing-hua SEISMOLOGY AND GEOLOGY    2025, 47 (1): 246-266.   DOI: 10.3969/j.issn.0253-4967.2025.01.015 Abstract （281）   HTML （10）    PDF（pc） （11655KB）（56）       Knowledge map    Save This study analyzes terrestrial time-varying gravity data from the southeastern margin of the Tibetan Plateau, covering the period from 2014 to 2022. Using the Bayesian adjustment method, we first captured temporal variations in the regional gravity field at different time scales. Then, the Tesseriod model was applied to simulate the field source medium and construct an equivalent source model. The gravity network's ability to resolve field sources was further evaluated using a checkerboard model. In regions with high source resolution, we inverted the apparent density variations of equivalent sources to examine tectonic changes and earthquake generation. The main findings are as follows: 1)The gravity network effectively reflects recent regional earthquakes(M≥5.0), with most events occurring in the centers of four quadrants of gravity variation or within high-gradient zones of positive and negative anomalies. 2)Analysis of the field source resolution capability, based on various checkerboard models, indicates that most areas of the gravity survey network have a resolution better than 1°×1°, except at the network edges. Notably, resolution improves to 0.5°×0.5° near the Dali, Anninghe-Zemuhe-Xiaojiang fault, and Xichang regions, along the boundary of the Grade I active block. 3)Long-term gravity field inversion results reveal apparent density changes ranging from -1.2kg/m3 to 1.2kg/m3 within 1km-thick equivalent layers at depths of up to 20km. This variation is approximately 0.4‰ of the average crustal density. Spatially, regions of increased apparent density correlate with active faults along the western boundary of the Sichuan-Yunnan block(near Dali-Xiangcheng)and the Xiaojiang fault zone on its eastern boundary. 4)Apparent density changes indicate energy accumulation preceding the Yangbi MS6.4 earthquake and two M5.0 earthquakes in Tonghai. The data capture pre-earthquake tectonic activity and subsequent crustal adjustments that led to decreased apparent density post-earthquake. Energy accumulation for the Yangbi earthquake is inferred to have started in 2015, driven by southward extrusion of materials along the eastern edge of the Tibetan Plateau and deep crustal migration. The complex location of the epicenter—at the intersection of the Weixi-Qiaohou and Honghe fault zones—may explain the area's frequent seismicity. Moreover, this region is characterized by low velocity and high conductivity, suggesting that fluid-channel materials surged into the source area, reactivating previously unmapped faults and triggering the Yangbi earthquake. Apparent density changes along the southern Xiaojing fault zone similarly show stress accumulation before the Tonghai M5.0 earthquakes, followed by a notable post-earthquake decrease and a rising trend in density between 2021 and 2022. The southern Xiaojing fault zone thus warrants close monitoring as a significant earthquake-prone region. 5)The long-term increase in apparent density results from continued southward or southeastward material extrusion and deep crustal migration along the southeastern margin of the Tibetan plateau. The spatial distribution aligns with previously identified low-velocity and high-conductivity areas. 6)Apparent density fluctuations correspond to the spatiotemporal distribution of M≥5 earthquakes, with these events often occurring at the edges of regions with increased density or at transitions between positive and negative density zones, aligning with the “hypocentroid and epicentroid” principle. In summary, this study documents gravity field and apparent density variations across the region, providing insights for quantitative interpretation in geological and geophysical research. These findings help identify deep field source signals associated with earthquake generation, reveal relationships between regional gravity field variation and tectonic movement, and offer a better understanding of dynamic process in deep crust in the Tibetan Plateau. Table and Figures | Reference | Related Articles | Metrics

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PRECISE JUDGMENT AND THINKING ON THE 2022 MENYUAN MS6.9 AND LUDING MS6.8 EPICENTERS ZHU Yi-qing, ZHAO Yun-feng, WEI Shou-chun, ZHANG Guo-qing, LIU Fang SEISMOLOGY AND GEOLOGY    2025, 47 (1): 235-245.   DOI: 10.3969/j.issn.0253-4967.2025.01.014 Abstract （276）   HTML （11）    PDF（pc） （2403KB）（86）       Knowledge map    Save In 2022, the Menyuan MS6.9 and Luding MS6.8 earthquakes occurred successively in the north-south seismic belt of China, both of which caused severe property damage. Prior to these two earthquakes, the China Earthquake Administration conducted multiple ground gravity observations in the North-South seismic zone. It successfully made mid-term predictions based on mobile gravity observation data. The actual epicenters of the two earthquakes were not more than 56km away from the center of the predicted earthquake risk zone in 2022, especially in the precise determination of the epicenter position in 2021 and the distance between the actual epicenter and the predicted epicenter was not more than 10km. This article analyzes ground gravity fields' dynamic evolution characteristics and laws at different temporal and spatial scales before the 2022 Menyuan MS6.9 and Luding MS6.8 earthquakes. It reviews the prediction process and basis of these two earthquakes, which is helpful for the study of medium and short-term earthquake prediction. Overall processing and analysis of multi-source gravity observation data in the north-south seismic zone, obtaining regional gravity field changes based on absolute gravity as the unified benchmark in the measurement area and analysis and study of the dynamic changes of the regional gravity field at different spatiotemporal scales before the Menyuan MS6.9 and Luding MS6.8 earthquakes. Further study of the spatiotemporal distribution characteristics and precursor mechanisms of regional gravity field changes will be done by combining geological tectonic dynamic environment and strong regional seismic activity events. 1)Before the Menyuan MS6.9 earthquake, the gravity change first appeared as a gradient zone of gravity change that was consistent with the direction of the Qilian Mountain fault structure belt and then showed certain four-quadrant distribution characteristics around the epicenter area. The earthquake occurred at the center of the four quadrants of gravity change and near the zero value line of gravity change. 2)Before the Luding MS6.8 earthquake, the gravity change first showed a gradient zone of gravity change that was consistent with the direction of the Xianshuihe fault structural belt and then showed significant four-quadrant distribution characteristics around the epicenter area. The earthquake occurred at the center of the four quadrants of gravity change and near the zero-value line of gravity change. 3)Gravity data reflects both earthquakes well, and obvious four quadrant distribution characteristics and high gradient zones of gravity changes were observed in the epicenter area and its vicinity before the earthquake, which may be gravity precursor information observed during the earthquake preparation process. In the past, it was very difficult to accurately determine the location of the three elements of earthquakes(time, location, and magnitude). However, suppose potential strong earthquake epicenters and possible magnitudes are delineated. In that case, the determination of the three elements of earthquakes in the future will become the determination of one element, which will greatly improve the prediction ability of earthquakes The next step is how to carry out earthquake monitoring and tracking work in the identified potential epicenter area and its vicinity, which may help with short-term and imminent prediction. Mobile gravity measurement is the main observation method for exploring earthquake prediction. By establishing a high-density atomic gravimeter absolute gravity observation network or a relative gravity observation network with reasonable absolute gravity control and conducting intensive monitoring, it is possible to reveal the distribution characteristics of underground structures near the epicenter of high-risk areas and extract absolute gravity change signals accompanying source changes during the preparation process of strong/large earthquakes, Develop its application and research in short-term earthquake prediction. Table and Figures | Reference | Related Articles | Metrics

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DENSE BENDING MOMENT NORMAL FAULT SCARPS ALONG THE GUMAN ANTICLINE AT THE FOOTHILL OF THE WEST KUNLUN MOUNTAINS XU Jian-hong, CHEN Jie, LI Tao, ZHANG Bo-xuan, DI Ning SEISMOLOGY AND GEOLOGY    2025, 47 (2): 405-428.   DOI: 10.3969/j.issn.0253-4967.2025.02.20240148 Abstract （276）   HTML （15）    PDF（pc） （15306KB）（78）       Knowledge map    Save Bending-moment fault and flexural-slip fault are two types of fold-related faults in compressional tectonic environments. Historical earthquake records suggest that both fault types may be active simultaneously, with their fault scarps providing crucial insights into strong seismic events. In the northern region of the Guman anticline, located at the foothills of the West Kunlun Mountains, numerous prominent bending-moment normal fault scarps have developed, reaching heights between 0.5m and 16.0m. This study focuses on a fault scarp segment approximately 5.4km long and 4.2km wide. A digital elevation model(DEM)with a 0.2m resolution was generated using drone photogrammetry. A total of 739 cross-fault scarp profiles were extracted, providing key parameters such as scarp height, slope, displacement continuity, and cumulative displacement trends. Data analysis yielded the following findings: (1)In the study area, dense bending-moment normal faults align along the active anticline axis, dipping toward the axial plane at angle of 70°~80°, as observed in a trench. Among these faults, more than a dozen dip northward, whereas only 1-2 dip southward, forming asymmetric grabens. This asymmetry may be attributed to the overall northward tilt of the strata and the differing limb structures of the underlying anticline. These faults divide the terrace surfaces into multiple rectangular blocks, 380~650m wide. The blocks exhibit outward tilting relative to the fold axis, with those cut by north-dipping faults tilting southward and those cut by south-dipping faults tilting northward. The degree of tilting and fault displacement is closely related to the thickness of the underlying anticlinal strata and the extent of stratal bending. (2)Displacement profiles along the faults reveal a step-like decrease in displacement as terrace surfaces become progressively younger, with maximum slope profiles displaying similar trends. This pattern suggests long-term fault activity. Cumulative displacement data confirm this trend, with displacement values of(54.5±3.3)m for terrace T3c and(19.5±1.1)m for terrace T1c. The total displacement of T3c is approximately 2.8 times that of T1c, and displacement ratios across different terraces range from 1.5 to 5.5. Higher ratios indicate greater displacement accumulation on older terraces, suggesting an earlier onset of fault activity. These displacement rankings imply that an initial framework of faults developed in the region, followed by subsequent fault intrusion. Notably, Fault F8 exhibits a displacement ratio of 5.5, forming a(1.0±0.3)m high fault scarp on the young T1b terrace, indicating that even the earliest-formed faults remain active. (3)Seismic reflection profiles reveal that the south flank of the Guman anticline dips 3°~6° northward, while the north flank dips 12°~14° northward. The underlying blind thrust exhibits a lower flat-ramp-upper flat geometry. However, bending-moment normal faults are not visible in the seismic reflection data, suggesting that they are secondary structures associated with anticline deformation. The fault zone aligns with the anticline’s fault-bend axis, indicating ongoing activity in the anticline zone. The bending-moment normal faults are rootless, meaning they are not primary seismogenic faults. Instead, they primarily develop in poorly layered strata and are largely independent of the kinematics of fold growth. Their formation is closely tied to the degree of strata bending and the thickness of overlying beds. Despite their shallow nature, the bending-moment normal faults exhibit long-term activity, providing evidence that the underlying anticline remains active. These findings support the interpretation of the Guman anticline as an active fault-bend fold. Table and Figures | Reference | Related Articles | Metrics

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HIGH-RESOLUTION SHALLOW CRUSTAL S-WAVE VELOCITY STRUCTURE IMAGING IN THE KASHGAR, XINJIANG HUA Qian, PEI Shun-ping, LI Tao, LIU Han-lin, LIU Wei, LI Lei, LI Jia-wei, YANG Yi-hai SEISMOLOGY AND GEOLOGY    2025, 47 (2): 533-546.   DOI: 10.3969/j.issn.0253-4967.2025.02.20240160 Abstract （276）   HTML （20）    PDF（pc） （7312KB）（104）       Knowledge map    Save High-density short-period seismometers are increasingly employed in urban environments and local geological structures to explore the crustal structure, their high-resolution images facilitate the precise identification of subsurface faults, the spatial distribution of mineral resources, and conduct building response analysis. In this study, 101 short-period seismometers were deployed across Kashgar for continuous seismic monitoring. Integrating with ambient noise tomography, high-resolution seismic velocity imaging of the shallow crust within the Kashgar was conducted. This study aims to delineate potential subsurface faults, elucidate their tectonic genesis, and provide critical insights for regional seismic risk assessment. The empirical Green’s functions extracted from the cross-correlation of the Z component yielded a total of 1 752 Rayleigh wave phase velocity and group velocity dispersion curves. By applying one-step ambient noise tomography, the three-dimensional S-wave velocity structure of the study area was resolved down to a depth of 5km, achieving a lateral resolution of approximately 0.04°. The horizontal and vertical cross-sections of the S-wave velocity model reveal that the S-wave velocities within the upper 5km of the crust in the study area are generally lower than the global average velocity model. The Kashgar Depression is characterized predominantly by Cenozoic sediments, with continuous Quaternary alluvial deposits reaching thicknesses of up to 10~12km. The relatively weak Cenozoic sedimentary basin likely contributes to the overall low S-wave velocities observed in the region. The velocity structures exhibit remarkably consistent patterns in varying depths. Below the depth of 1.2km, three notable low-velocity anomalies(LVAs), labeled L1, L2, and L3, are identified beneath the Kashgar. Among these, L1 and L2 form an approximately 16km long, east-west trending bowtie-shaped LVAs that align with the structural trend of the Kashgar anticline. These anomalies cover much of central Kashgar and extend nearly vertically to depths shallower than 5km, showing variation in shape and size at different depths. L3, located at the central southern edge of Kashgar, appears as a semicircle with a diameter of about 10km. Its extent diminishes gradually with increasing depth, which may indicate lithological variations at different depths. Based on the integration of seismic reflection profiles, we infer that the frontal zone of the Southwestern Tianshan fold-and-thrust belt has developed multiple north-dipping thrust structures and south-dipping secondary thrust faults propagating toward the basin. These deformations penetrate the entire sedimentary cover, forming multi-level detachments at varying depths. Notably, the slippage of the mud layer(approximately 4km deep)at the base of the sedimentary cover in the Kashgar Depression represents the shallowest detachment layer identified in previous studies. This suggests that the multi-layered weak slippage zones within the sedimentary sequence of the Kashgar Depression may be responsible for the formation of the bowtie-shaped LVAs. Mechanically weak detachment layers likely play a key role in shaping these anomalies. Furthermore, the Kashgar-Atushi fold-and-thrust system has experienced both lateral propagation and along-strike shortening during ongoing tectonic activity, resulting in the progressive advancement of the fold-and-thrust system towards the Kashgar Depression, which lies adjacent to the collapse-reverse fault system, may also have been subjected to intense tectonic action to form similar faults. Consequently, the east-west trending bowtie-shaped LVAs may indicate the presence of a secondary blind fault parallel to the Kashgar anticline. This inferred fault crosses the tectonic boundary between the southwestern Tianshan and Pamir regions, exhibiting a significant east-west structural discontinuity. Geological and geomorphological evidence reveals that the Kizilsu River, the largest river in the region, and its tributaries intersect the LVAs beneath Kashgar. We hypothesize that these LVAs may also reflect high-porosity fluvial sediments and folded scarps associated with paleo-river deformation. In summary, high-density short-period seismic array imaging enables the precise detection of shallow subsurface structures in urban environments. This approach provides robust datasets for urban active fault detection, seismic amplification effect evaluation, and subsurface resources and energy exploration and development. Table and Figures | Reference | Related Articles | Metrics

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COMPARISON OF THE CHARACTERISTICS OF EARTHQUAKE SEQUENCE AND INTENSITY OF THE JANUARY 7, 2025 MS6.8 DINGRI EARTHQUAKE IN XIZANG WU Xiao-fei, MENG Ling-yuan SEISMOLOGY AND GEOLOGY    2025, 47 (3): 869-880.   DOI: 10.3969/j.issn.0253-4967.2025.03.20250044 Abstract （274）   HTML （5）    PDF（pc） （7125KB）（39）       Knowledge map    Save At 09:05 on January 7, 2025, a magnitude MS6.8 earthquake struck Dingri County, Shigatse City, in the Xizang Autonomous Region of China. The earthquake had a focal depth of 10km and is the largest event in the region in recent years, resulting in severe damage and a wide area of impact. The disaster caused over 120 fatalities, damaged approximately 27,000 dwellings, and led to the collapse of 3600 structures. This study presents a comprehensive analysis incorporating seismogenic structures, historical seismicity, earthquake sequence evolution, and intensity mapping. The epicenter is located within the Lhasa Block of the Tibetan Plateau, in the high-altitude valleys and basins north of the Himalayan mountain range, where elevations exceed 4,000m within a 10km radius. The tectonically active Lhasa Block includes multiple fault systems. The earthquake likely originated on the Dengmecuo fault, a segment of the Shenza-Dinggye Rift fault zone, which trends approximately north-south. Since 1900, the region within 300km of the epicenter has experienced 15 earthquakes of magnitude MS6.0-6.9, and notable larger events include the MS8.1 Nepal earthquake of April 25, 2015, and its aftershocks. According to the China Earthquake Networks Center, the event had a moment magnitude of MW7.1 and a centroid depth of 15km. The focal mechanism indicates normal faulting. The radiated seismic energy was approximately 1015 J. The moment and energy magnitudes both exceed the surface-wave magnitude, suggesting an efficient release of seismic moment and energy during rupture. The aftershock sequence extends approximately 75km in a north-south direction, aligned with the inferred fault strike. Aftershocks were concentrated near the mainshock and its northern extent, separated by a relatively quiet central segment. Intensity analysis indicates a maximum intensity of Ⅸon both the United States Geological Survey(USGS)simulated intensity map and the measured intensity map from the China Earthquake Administration. The meizoseismal area follows a north-south distribution consistent with the fault trend. The Ⅵ-degree isoseismal zone in the USGS map extends nearly 200km in a north-south orientation, while the measured map shows isoseismal lines trending NNE, with a long axis of about 191km and a short axis of 152km. The orientations of the isoseismal lines and the meizoseismal area in both maps are broadly consistent, though discrepancies exist in areal extent and coverage. Notably, the simulated intensity in the northern part of the aftershock zone is higher than that of observed. This discrepancy likely arises from the fact that the area is sparsely populated, with no significant structural damage or reported casualties. Table and Figures | Reference | Related Articles | Metrics

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LATE QUATERNARY DEFORMATION RATE OF THE WENSU FORELAND THRUST BELT IN THE SOUTHERN TIANSHAN MOUNTAINS ZANG Ke-zhi, WU Chuan-yong, ZHANG Jin-shuo, GAO Zhan, YUAN Si-hua, YUAN Hai-yang, YU Xiao-hui, WANG Xue-zhu SEISMOLOGY AND GEOLOGY    2024, 46 (6): 1280-1294.   DOI: 10.3969/j.issn.0253-4967.2024.06.004 Abstract （274）   HTML （37）    PDF（pc） （9480KB）（124）       Knowledge map    Save In response to the ongoing India-Eurasia collision in the late Cenozoic, the Tianshan orogenic belt was reactivated and experienced rapid uplift. Strong uplifted topography results in that the mountains propagate from the range front toward the foreland basin to form several fan-shaped foreland thrust belts both on its north and south sides. These foreland thrust belts accommodate the most north-south convergence strain and control the regional deformation pattern. However, in contrast to the well-studied foreland thrust belts, the kinematics and deformation rate of the transition area between different foreland thrust belts have not been well-documented. Therefore, it is still unclear how the crustal shortening in the foreland basins changes along the east-west direction. Further, the deformation characteristics and seismic hazard in this region are poorly understood because quantitative information on active deformation is lacking. The Wensu foreland thrust belt is located in the Kalpin and Kuqa foreland thrust systems' transition areas. In contrast to the Kuqa and Kalpin foreland thrust belts at its east and west sides, the Wensu foreland thrust belt propagated approximately 20km toward the basin and only developed one row of active thrust fault-anticline belts, namely the North Wensu thrust fault-anticline belt. The North Wensu structural belt shows clear evidence of tectonic solid activity because the late Quaternary sediments and river terraces have been faulted. However, this structural belt's kinematics and late Quaternary deformation rate remain poorly constrained. This study quantifies its deformation mode based on field geological mapping across the anticline. Our results indicate that the North Wensu structural belt is a fault-bending fold. Based on interpretations of detailed high-resolution remote sensing images and field investigations, five levels of river terraces can be identified along the Kekeya River valley. By surveying of the displaced terraces with an unmanned drone, the crustal shortening values of ~20.7m、 ~35.3m and ~46.9m are determined for the T3, T4 and T5 terraces, respectively. Our optically stimulated luminescence(OSL)dating yields a depositional age of(9.02±0.55)ka for the T3 terrace, (24.23±1.58)ka for the T4 terrace, and(40.43±3.07)ka for the T5 terrace. Thus, we estimate a crustal shortening of ~1.31mm/a in the late Quaternary(since approximately 40ka), and approximately 2.29mm/a in the Holocene for the North Wensu structural belt. Our results indicate that the deformation rate of the North Wensu structural belt exhibits an obvious increase in the Holocene. This phenomenon indicates that the strong earthquake activity on the North Wensu thrust belt has increased significantly in the Holocene, implying an irregular activity habit of the strong earthquake recurrence cycle on this tectonic belt. The propagation deformation toward the basin of the Wensu foreland thrust belt is very limited. Therefore, we suggest that the foreland thrust belt is a thick-skinned nappe structure and is dominated by high-angle thrust faulting. The tectonic deformation in the Wensu region seems to be characterized by considered vertical growth. Although the deformation rate is small, the uplift amplitude is significant in this region. Table and Figures | Reference | Related Articles | Metrics

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THREE-DIMENSIONAL SURFACE COSEISMIC DISPLACEMENTS FROM DIFFERENCING PRE- AND POST-EARTHQUAKE TERRAIN POINT CLOUDS WEI Zhan-yu, HE Hong-lin, DENG Ya-ting, XI Xi SEISMOLOGY AND GEOLOGY    2025, 47 (1): 167-188.   DOI: 10.3969/j.issn.0253-4967.2025.01.011 Abstract （272）   HTML （13）    PDF（pc） （12329KB）（92）       Knowledge map    Save After a major earthquake, in addition to determining the location and magnitude of the earthquake, the analysis of the coseismic displacement and deformation patterns near the seismic rupture zone is equally critical, which is crucial for an in-depth understanding of the seismic rupture process, fault behavior, and the relationship between active faults and topography. Although the geodetic techniques for observing the coseismic displacement field of the earth's surface at various spatial and temporal scales are developing rapidly, obtaining a detailed seismic rupture zone and displacement field remains challenging. Current techniques for obtaining these measurements, including Global Navigation Satellite Systems(GNSS), radar or optical remote sensing, and field observations, have their respective limitations regarding observation density, coverage area, measurement dimensions, and operational efficiency. Recently, the widespread adoption and application of high-precision and high-density topographic observation technologies(such as SfM and LiDAR)have enabled geomorphologists and geologists to capture various Earth surface features with unprecedented spatiotemporal resolution and detail. This has made it possible to map detailed three-dimensional displacement fields. This paper introduces an Iterative Closest Point(ICP)algorithm that uses pre- and post-earthquake topographic point clouds to determine near-field three-dimensional coseismic surface displacements. The main purpose of developing this algorithm is to quickly provide data on the coseismic displacement field near the seismic rupture zone after a major earthquake, compensating for the deficiencies of existing geodetic measurements or field observations. To test the applicability and workflow of the ICP algorithm for obtaining topographic data through aerial photogrammetry in the Sichuan-Yunnan region, we selected two sets of SfM topographic point cloud data from the Jiaoji River fault on the Daliangshan fault zone. By superimposing the coseismic deformation field to simulate the pre-earthquake and post-earthquake topographic point cloud sets, we explored the accuracy of this method under different grid sizes and point cloud densities. This method can accurately recover the direction and magnitude of the coseismic displacement field under a grid size exceeding 50 meters, with horizontal and vertical accuracies of approximately 20cm and 10cm, respectively, comparable to the positioning accuracy of the topographic point clouds. As the point cloud density and grid window size decrease, the accuracy of this method in recovering co-seismic displacement fields declines. By analyzing the potential impact of terrain changes such as tree growth, house construction, and river erosion on displacement field recovery, the results show that increasing the grid size allows pre- and post-earthquake point clouds to have sufficient terrain structure for matching, reducing the impact of local terrain changes on displacement field recovery. The grid window size is a trade-off between 1)a large scale with sufficient terrain structure and 2)a smaller scale with finer resolution. The ICP method, utilizing high-precision point clouds from before and after the earthquake, can obtain detailed three-dimensional surface displacement fields near earthquake rupture zones, providing new constraints for shallow fault slip and rupture zone deformation and aiding the study of seismic rupture processes and fault growth. Table and Figures | Reference | Related Articles | Metrics