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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 （3303）   HTML （148）    PDF（pc） （13725KB）（1344）       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.

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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 （1131）   HTML （43）    PDF（pc） （6150KB）（839）       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.

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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 （1664）   HTML （28）    PDF（pc） （5289KB）（616）       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.

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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 （1468）   HTML （36）    PDF（pc） （18854KB）（514）       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.

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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 （1026）   HTML （37）    PDF（pc） （7758KB）（488）       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.

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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 （1219）   HTML （52）    PDF（pc） （13633KB）（432）       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.

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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 （1448）   HTML （32）    PDF（pc） （3649KB）（425）       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.

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    THREE-DIMENSIONAL MODEL OF SEISMOGENIC FAULT AND SEISMIC ENVIRONMENT OF XIZANG DINGRI MS6.8 EARTHQUAKE OF JANUARY 7, 2025
    GUO Zhao-wu, LU Ren-qi, ZHANG Jin-yu, FANG Li-hua, LIU Guan-shen, WU Xi-yan, SUN Xiao, QI Shi-miao
    SEISMOLOGY AND GEOLOGY    2025, 47 (3): 671-688.   DOI: 10.3969/j.issn.0253-4967.2025.03.20250030
    Abstract （835）   HTML （52）    PDF（pc） （7098KB）（406）       Save

    At 09:05a.m. on January 7, 2025, a magnitude MS6.8 earthquake struck Dingri County, Xizang, China, resulting in 126 fatalities and a maximum seismic intensity of Ⅸ. Occurring within a seismically active and tectonically complex region, this event drew significant attention from both the scientific community and the public. The epicenter was located near the Dengmecuo Fault, which has been preliminarily identified as the seismogenic fault.

    This study utilized publicly available geological survey data, aftershock relocations, and focal mechanism solutions to construct a detailed three-dimensional geometric model of the Dengmecuo Fault. The model was developed using the SKUA-GOCAD 3D modeling platform, enabling a comprehensive analysis of the fault’s geometry. Results reveal pronounced geometric segmentation along the fault plane, with the spatial distribution of these structural features closely correlating with observed seismicity, highlighting the influence of fault geometry on earthquake generation.

    The MS6.8 Dingri earthquake occurred near a prominent structural irregularity on the Dengmecuo Fault, at point P3, where the fault plane bends into an eastward-projecting arc. This three-dimensional structural mutation likely played a role in the nucleation of the event, underscoring the relationship between fault complexity and seismic rupture. The Dengmecuo Fault, situated in the southern Tibetan plateau, is a listric normal fault characterized by a steep upper section and a gentler lower section that terminates within a detachment layer in the upper crust. It does not extend into the deeper lithosphere, indicating that it is part of the region’s shallow normal fault system. The earthquake is interpreted as the release of accumulated stress along this shallow fault structure.

    To evaluate post-earthquake stress transfer and seismic hazard, Coulomb stress modeling(Coulomb 3.4)was conducted. The analysis indicates that several regional faults are now in a state of increased Coulomb stress, including the southern segment of the Dengmecuo Fault, the middle segment of the south Xizang detachment system, the southern segment of the Shenzha-Dingjie Fault, the central Yarlung-Zangbo Fault, and the midsection of the Dajiling-Angren-Renbu Fault. These fault segments are identified as potential sites for future seismic activity and merit heightened monitoring.

    This study presents a detailed characterization of the three-dimensional geometry of the seismogenic fault responsible for the Dingri MS6.8 earthquake and offers a preliminary analysis of regional seismogenic structures. The findings provide valuable insights into the tectonic setting of southern Xizang and contribute to the assessment of regional seismic hazard.

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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 （1833）   HTML （25）    PDF（pc） （10539KB）（397）       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.

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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 （1878）   HTML （34）    PDF（pc） （5804KB）（387）       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.

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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 （1285）   HTML （49）    PDF（pc） （6115KB）（384）       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.

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    SEISMOGENIC FAULT OF THE TANGSHAN MS5.1 EARTHQUAKE ON JULY 12, 2020 AND ITS IMPLICATIONS FOR REGIONAL TECTONICS
    CAO Jun, ZHOU Yi, GAO Chen, LIU Shu-feng, CHEN An, ZHANG Su-xin, FENG Xiang-dong, WU Peng, CHEN Zhao-dong
    SEISMOLOGY AND GEOLOGY    2024, 46 (5): 993-1011.   DOI: 10.3969/j.issn.0253-4967.2024.05.001
    Abstract （1546）   HTML （72）    PDF（pc） （10827KB）（383）       Save

    On July 12, 2020, a M5.1 earthquake occurred in the Guye District of Tangshan City. This earthquake is notable as the only moderate seismic event exceeding magnitude 5 in the Tangshan area over the past two decades. However, the exact seismogenic fault responsible for this earthquake remains undetermined, complicating efforts to assess future seismic risks in the region. Post-earthquake damage assessments revealed that the macroseismic damage was distributed along two primary fault zones: a long northwest(NW)trending band and a short northeast(NE)trending band. The most significant damage occurred at the intersection of these two bands. Based on the regional geological structure and stratigraphy, field surveys identified the NE-trending Tangshan-Guye fault as a Holocene-active fault, while the NW-trending Mozhouyu fault was classified as a Quaternary fault within the area of greatest damage. Analysis of Sentinel-1A InSAR time-series data revealed differential deformation along the Mozhouyu fault. Relocation results of earthquakes greater than magnitude 1.0 over the past decade in the Tangshan region showed seismic activity distributed in two primary bands. One band aligns with the NE-trending Tangshan-Guye fault, with concentrated activity at its intersection with the Mozhouyu fault. Following the M5.1 earthquake, multiple authorities determined that the focal mechanism indicated a strike-slip earthquake, with two conjugate planes oriented in the NE and NW directions. This finding is consistent with the alignments of the Tangshan-Guye and Mozhouyu faults. Through comprehensive analysis, including post-earthquake field surveys, regional deformation data, and the relocation of smaller seismic events, it was concluded that the surface damage from the Tangshan Guye earthquake followed both NE and NW orientations. Of the two intersecting faults in the damaged area, the Mozhouyu fault is a middle Pleistocene fault, while the Tangshan-Guye fault is the most significant Holocene-active fault in the region. The characteristics of these conjugate faults align with both the source parameters and relocated seismic sequences of the Tangshan Guye earthquake. The right-lateral strike-slip motion along the Tangshan fault zone, combined with regional NE—NEE-directed compressive stress, likely caused the Tangshan-Guye fault to be blocked by the Qinglongshan complex anticline during its eastward expansion. Subsurface data further indicate that the Qinglongshan complex anticline marks a boundary of regional physical property differences. Therefore, it is concluded that the Tangshan-Guye fault and the Mozhouyu fault were the conjugate seismogenic faults responsible for the M5.1 earthquake on July 12, 2020.

    The Tangshan Guye earthquake is a typical moderate-intensity strike-slip event in the North China Plain. An analysis of 705 focal mechanism solutions from 2002 to 2020 indicates that most earthquakes in the region are predominantly strike-slip in nature. Historical strong earthquakes in the North China Plain also exhibit high-angle strike-slip faults as their primary seismogenic structures, a conclusion supported by extensive seismological research. A substantial body of seismic studies suggests that the failure of the North China Craton during the early Cenozoic was driven by crustal extension, resulting in the formation of listric(shovel-shaped)normal faults. However, these faults are no longer the main seismogenic structures for present-day earthquakes. Since the late Pleistocene, tectonic activity in the North China Plain has been characterized by the development of new, steeply dipping strike-slip faults, which cut through the older listric normal faults. These steep dip strike-slip faults have become the primary seismogenic structures responsible for regional seismicity. Future seismic hazard assessments in the North China Plain should focus on the activity of these steep dip faults, as they are more likely to generate significant earthquakes. This shift in tectonic stress is attributed to a combination of factors, including the eastward expansion of the Tibetan Plateau, the rigid deformation of the Ordos Block, and the westward subduction of the Pacific and Philippine plates. Since the late Pleistocene, these forces have redefined the tectonic landscape of the region, increasing the likelihood of strike-slip faulting.

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    SEISMOLOGY AND GEOLOGY    2024, 46 (6): 0-0.  
    Abstract （166）      PDF（pc） （273KB）（368）       Save
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    A NEW REFERENCE SCHEME FOR THE DELINEATION OF ACTIVE BLOCK BOUNDARIES IN THE SICHUAN-YUNNAN EXPERIMENTAL SITE
    SUN Xiao, LU Ren-qi, ZHANG Jin-yu, WANG Wei, SU Peng
    SEISMOLOGY AND GEOLOGY    2024, 46 (5): 1027-1047.   DOI: 10.3969/j.issn.0253-4967.2024.05.003
    Abstract （839）   HTML （52）    PDF（pc） （9302KB）（363）       Save

    Active block boundaries represent areas where significant crustal stress accumulates, leading to concentrated tectonic deformation and frequent seismic activity. These boundaries are crucial for understanding the patterns of strong earthquakes within mainland China. The China Seismic Experimental Site, located in the Sichuan-Yunnan region, is a key area of tectonic deformation caused by the collision and convergence of the Indian and Eurasian plates. This region plays a vital role in transferring tectonic stress between western China and adjacent plates.

    This comprehensive study analyzes the integrity, three-dimensional characteristics, hierarchy, and tectonic activity of blocks within the Sichuan-Yunnan region, following established schemes and criteria for defining active block boundaries. After detailed research, the major active fault zones in the region have been divided into three primary active block boundary zones and sixteen secondary boundary zones.

    A new reference scheme was developed by considering several factors, including the historical distribution of strong earthquakes, the hierarchical patterns of earthquake frequency and magnitude, spatial variations in present-day deformation as revealed by GNSS data, and deep crustal differences indicated by gravity data and velocity structures. The Jinshajiang-Honghe Fault, Ganzi-Yushu-Xianshuihe-Anninghe-Zemuhe-Xiaojiang Fault, and Longmenshan Fault are identified as the primary active block boundary zones, while faults such as the Lijiang-Xiaojinhe, Nantinghe, and Longriba faults are classified as secondary boundary zones.

    Through an integrated analysis of seismic activity, current deformation patterns, fault sizes, deep crustal structures, and paleoseismic data, the study estimates that the primary boundary zones have the potential to generate earthquakes of magnitude 7.5 or greater, while the secondary boundary zones could produce earthquakes of magnitude 6.5 or greater.

    The expansion of geophysical exploration, including shallow and deep earth data, has allowed for a transition in the study of active tectonics from surface-focused to depth-focused, from qualitative to quantitative, and from two-dimensional to three-dimensional analysis. By integrating multiple data sources, i.e. regional geology, geophysics, seismicity, and large-scale deformation measurements, this study presents a more refined delineation of active blocks in the Sichuan-Yunnan region.

    The new delineation scheme provides a scientific basis for future mechanical simulations of interactions between active blocks in the Sichuan-Yunnan Experimental Site. It also offers a framework for assessing the probability of strong earthquakes and evaluating seismic hazards. The purpose of this study is to re-analyze and refine the delineation of active block boundaries using high-resolution, coordinated data while building on previous research.

    In summary, the Sichuan-Yunnan region’s primary fault zones are divided into three primary and sixteen secondary active block boundary zones. The study concludes that primary boundary zones are capable of generating magnitude 7.5 or greater earthquakes, while secondary zones can produce magnitude 6.5 or greater earthquakes. While the current block delineation scheme offers a valuable foundation, further discussion and refinement of certain secondary boundary zones are needed as detection and observational data improve. This study provides an essential framework for analyzing the dynamic interactions between active blocks, identifying seismogenic environments, and assessing seismic risks in the Sichuan-Yunnan region.

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    S-WAVE VELOCITY STRUCTURE IN SHANGHAI AND ADJACENT AREAS BASED ON AMBIENT NOISE TOMOGRAPHY
    FENG Ce, SONG Xiu-qing, WANG Ren-tao, LIU Hao-lan
    SEISMOLOGY AND GEOLOGY    2024, 46 (6): 1374-1390.   DOI: 10.3969/j.issn.0253-4967.2024.06.009
    Abstract （537）   HTML （26）    PDF（pc） （10104KB）（299）       Save

    The Shanghai region is located south of the Yangtze River estuary, at the eastern edge of the Lower Yangtze Platform formed during the late Proterozoic Jinning cycle. The East China region is currently in the late stage of the second phase of seismic activity response, with heightened seismic activity expected to continue. The study area is characterized by numerous faults, including significant structures like the Xiaoshan-Qiuchuan fault zone(Shanghai segment)and many smaller NE- and NW-trending shallow fault zones, which are intertwined and cross each other horizontally and vertically. Background noise tomography technology relies on seismic background noise data to compute the corresponding Green's functions through cross-correlation, using the results to image phase velocities and surface waves. This method is widely applied due to its high resolution, low cost, and independence from seismic source data.

    This study collected continuous vertical background noise data from 58 broadband mobile seismic stations in Shanghai and its neighboring areas over a year. Using background noise cross-correlation technology combined with a fast marching method(FMM)for imaging, we obtained the phase velocity structure of surface waves in the crust and upper mantle for 5s to 30s. Finally, using a least-squares linear inversion method, we derived a high-resolution 3D S-wave velocity structure from 5km to 30km below the study area.

    The results indicate that the Shanghai area's S-wave velocity structure exhibits specific lateral and vertical heterogeneity. The distribution of velocity anomalies in the shallow layer and upper crust at depths of 5km to 10km shows a correlation with local topography and the distribution of major faults, notably influenced by the Huzhou-Suzhou Fault. In the middle to lower crust at depths of 15km to 20km, velocity anomalies are demarcated by the Fengjing-Chuansha area, where velocities gradually increase from northern Jiangsu to Hangzhou Bay, with significant structural uplift along the Fengjing-Chuansha fault in Shanghai. At depths of 25km to 30km, the distribution of velocity anomalies reflects a “west-deep, east-shallow” burial state in the lower crust and upper mantle.

    From the analysis of three longitudinal profiles(AA', BB', CC'), we draw the following conclusions:

    (1)The underground structure of Shanghai and its vicinity shows a gradual change, with overall crustal thickness decreasing from west to east, characterized by a “thick west, thin east” profile and a topography of “low west, high east with a central uplift.” The shallow S-wave velocity significantly correlates with local topography; the velocity values in the middle to upper crust are predominantly controlled by major faults, especially the Huzhou-Suzhou fault. The middle to lower crust beneath Shanghai exhibits an uplifted structural form, with a “low west, high east” fluctuation in the lower crust and upper mantle.

    (2)The velocity anomalies and seismic activity are closely related to fault zones, with low-speed anomalies accompanying major faults. The distribution of earthquakes tends to cluster near low-speed bodies and fault zones, notably at the prominent uplift junctions beneath Taicang and Qingpu. The area's predominant occurrence of shallow-source earthquakes is likely due to stress imbalance between the fractured middle to the upper crust and the stable lower crust.

    (3)Low-speed anomalies have been consistently observed at depths of 5km to 25km in the Changshu region. Based on related literature and imaging results from this study, we hypothesize the potential presence of thermal material upwelling in the Changshu area.

    (4)The longitudinal profile results indicate that the thickness of the upper crust in the study area is approximately 12km, the middle crust around 10km, and the lower crust about 8km. Distinct layering within the crust is evident, with a gradual change in the middle to lower crust, while the upper crust shows significant heterogeneity. The influence of the faulting in the area controls the distribution of low-speed anomalies.

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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 （760）   HTML （21）    PDF（pc） （7235KB）（295）       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.

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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 （681）   HTML （30）    PDF（pc） （7786KB）（275）       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.

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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 （1020）   HTML （42）    PDF（pc） （9921KB）（273）       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.

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    RESEARCH ADVANCES OF THE LATE QUATERNARY ACTIVITY OF XIAOJIANG FAULT ZONE IN THE SOUTHEASTERN MARGIN OF QINGHAI-XIZANG PLATEAU
    CHANG Yu-qiao, ZHANG Hui-ping, ZHAO Xu-dong
    SEISMOLOGY AND GEOLOGY    2026, 48 (2): 279-313.   DOI: 10.3969/j.issn.0253-4967.20240135
    Abstract （618）   HTML （28）    PDF（pc） （9401KB）（268）       Save

    The Xiaojiang fault zone is the southernmost branch fault of the Xianshuihe-Xiaojiang left-lateral strike-slip fault system, together with the Xianshuihe Fault, the Anninghe Fault and the Zemuhe Fault, which forms the eastern boundary of the Sichuan-Yunnan block on the southeast margin of Qinghai-Xizang Plateau and plays an important role in accommodating the clockwise rotation around the eastern Himalayan syntaxis and S-SE extrusion of the Sichuan-Yunnan block. The scientific understanding of geometric structures, the slip rate, the strong earthquake recurrence and the mechanism of deformation compatibility of different segments of the Xiaojiang fault zone, especially the intersection with the Red River fault zone, remains highly debated. In order to better understand the role of the Xiaojiang fault zone in the process of material extrusion of the southeastern margin of the Qinghai-Xizang Plateau, based on the systematic summary of previous research results about the Xiaojiang fault zone, topographic relief and slope in the study area were extracted, and combined with geomorphological characteristics analysis, the geometric structure and kinematic characteristics, strike-slip rate at different time scales, seismic activity and deformation coordination with the Red River fault zone of the Xiaojiang fault zone are combed and summarized. combined with geomorphological characteristics analysis by extracting the relief and slope of the study area. The geometric segments and the late Quaternary activity characteristics of each segment of the Xiaojiang fault zone are described in detail. Then, we mainly reviewed the slip-rates at different timescales(geodetic scale, late Quaternary scale, and long time scale) of the Xiaojiang fault zone and their spatio-temporal variations. The seismicity characteristics of the Xiaojiang fault zone are summarized from three aspects: Paleoearthquakes, historical earthquakes and present earthquakes. The geometric relationship, deformation decomposition and transformation of faults at the intersection of the Xiaojiang fault zone and the Red River fault zone are analyzed. Besides, the geometric and kinematic characteristics of the deformation of the Xiaojiang fault zone and the coupling relationship between deep and shallow tectonic deformation are discussed, combined with geomorphic feature analysis. At last, he risk of future strong earthquakes in the Xiaojiang fault zone is discussed based on the results of previous studies on heterogeneous interseismic coupling along the Xiaojiang fault zone, etc. Through comprehensive analysis, it is concluded that the geometric and kinematic characteristics of the Xiaojiang fault zone are consistent with a clockwise rotation of the Sichuan-Yunnan block about the eastern Himalayan syntaxis. The deep tectonic process has an obvious controlling effect on the shallow tectonic deformation, and the Xiaojiang fault zone has a profound influence on the crustal structure, the deformation of the medium and the process of material migration. As the southeast boundary fault of the Sichuan-Yunnan block, the Xiaojiang fault zone has well restricted the S-SE movement of crustal material during the process of extrusion from the southeast margin of the Qinghai-Xizang Plateau to the east. The results show that the strike adjustment of the Xiaojiang fault zone, the change of movement characteristics, the spatio-temporal evolution of strike-slip rate, the segmentation of geomorphic parameters and the distribution of seismic activity are highly consistent with the clockwise rotation direction of the Sichuan-Yunnan block around the eastern Himalayan syntaxis. There is an obvious coupling relationship between deep tectonic action and shallow tectonic deformation in the Xiaojiang fault zone. The risk of strong earthquakes is high in the Xiaojiang fault zone, especially in the Qiaojia-Dongchuan area in the north and the confluence area of the Red River fault zone in the south. The probability of strong earthquakes in the future is increasing in each section of the Xiaojiang fault zone, especially in the northern section of the Qiaojia-Dongchuan fault zone and the intersection of the Red River fault zone and the Xiaojiang fault zone, the risk of strong earthquakes in the future is high, which should be paid great attention to.

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    LATE QUATERNARY THROW RATE OF THE SEISMOGENIC FAULT(DENGMECUO FAULT)OF THE 2025 MS6.8 DINGRI EARTHQUAKE IN SHIGATSE
    GAO Yang, WU Zhong-hai, HAN Shuai, TIAN Ting-ting
    SEISMOLOGY AND GEOLOGY    2025, 47 (3): 689-706.   DOI: 10.3969/j.issn.0253-4967.2025.03.20250034
    Abstract （554）   HTML （28）    PDF（pc） （10876KB）（267）       Save

    On January 7, 2025, a significant earthquake occurred in Dingri, Shigatse, China. Both the China Earthquake Networks Center and the USGS provide focal mechanism solutions indicating that the earthquake was a normal fault event. The epicenter was located in the Dengme Cograben, part of the southern segment of the Dinggye-Xainza rift, with the seismogenic fault identified as the bounding normal fault of the Dengme Cograben, the Dengmecuo fault. The late Quaternary throw rate of this fault is crucial not only for regional seismic hazard assessments but also for understanding the east-west extensional deformation within the Tibetan plateau. Previous studies on the kinematics of the Dengmecuo fault report varying throw rates: (0.28±0.04)mm/a since ~56ka, (0.28±0.04)mm/a since ~50ka, and(0.09±0.03)mm/a since ~95ka. However, the observed maximum coseismic vertical displacement of ~3m during the January 2025 earthquake suggests that the maximum cumulative time for this displacement is approximately 37ka, based on the published late Quaternary throw rate. This is inconsistent with the ~5ka elapsed time since the most recent earthquake on this fault, highlighting the uncertainty in the late Quaternary throw rate and limiting our understanding of strain partitioning and seismic risk in the southern Dinggye-Xainza rift.

    To resolve this uncertainty, we combine high-resolution remote sensing image interpretation with field geological and geomorphological surveys to determine the geometric distribution of the Dengmecuo fault. Two study sites were selected along the fault, each featuring clear faulted geomorphology suitable for dating. Low-altitude photogrammetry using an unmanned aerial vehicle(UAV)was combined with optically stimulated luminescence(OSL)and AMS 14C dating to refine the late Quaternary throw rate of the Dengmecuo fault and assess its seismic hazard.

    Our results show that the Dengmecuo fault, which strikes NNW and dips NW or W, is approximately 58km long and can be divided into northern, central, and southern segments. The northern segment is defined by the Laangshuiku area, while the southern boundary is located at the edge of Pum Qu. In the northern study site, vertical offsets of 19.2(+3.5/-2.3)m on the T2 alluvial fan and 8.0(+0.9/-0.7)m on the T1 alluvial fan correspond to formation ages of(28.3±1.4)ka and(12.0±1.5)ka, respectively. By matching the vertical offsets with their respective formation ages, we estimate a throw rate of (0.7±0.1)mm/a. However, the throw rate for the T1 fan is uncertain, as its vertical offset is smaller than the cumulative displacement since its formation. At the southern study site, combining a vertical offset of 5.3(+0.3/-0.5)m with the formation age of the T1 terrace ((9.2±1.0)ka), we calculate a throw rate of(0.6±0.1)mm/a.

    Overall, our results indicate late Quaternary throw rates of(0.7±0.1)mm/a since ~28ka and(0.6±0.1)mm/a since the Holocene. Additionally, using the relationship S=D/Rx, where S is the slip rate, D is displacement, and Rx is the recurrence interval, we estimate a slip rate of(0.5±0.1)mm/a based on the average value of the maximum displacement(2.5~3m)of 2025 Dingri MS6.8(Shigatse)earthquake as 2.75m and the interval of paleoseismic events during the Holocene as(5500±1100)a. This result is consistent with the throw rate of(0.6±0.1)mm/a since the Holocene determined from faulted geomorphic surfaces.

    Finally, combining the throw rate of (0.6±0.1)mm/a since the Holocene with the ~5ka elapsed time since the most recent earthquake, we conclude that the Dengmecuo fault had accumulated 2.5~3.5m of coseismic displacement before the 2025 Dingri MS6.8 earthquake, corresponding to a magnitude of MW6.9-7.0. These parameters align with the 2025 MS6.8 earthquake, indicating that the Dengmecuo fault posed a significant seismic risk prior to the event.

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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 （763）   HTML （27）    PDF（pc） （7728KB）（265）       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.

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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 （537）   HTML （41）    PDF（pc） （9480KB）（247）       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.

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    APPARENT RESITIVITY VARIATION AT KEPING SEISMIC STATION BEFORE THE MODERATE EARTHQUAKES IN SOUTH TIANSHAN AREA, XINJIANG
    LI Xin-yan, ZENG Xian-wei, LI Meng-ya, WEI Ding-jun, CUI Jin
    SEISMOLOGY AND GEOLOGY    2025, 47 (5): 1438-1455.   DOI: 10.3969/j.issn.0253-4967.2025.05.20240040
    Abstract （286）   HTML （11）    PDF（pc） （5554KB）（243）       Save

    The south Tianshan area is one of the main moderate earthquake preparation areas in China. Apparent resistivity monitoring has been demonstrated as an effective approach for intermediate-to short-term earthquake forecasting, as validated by numerous documented seismic cases. To improve regional seismic monitoring networks and observe the spatial and temporal variations in the apparent resistivity of shallow crust caused by the seismic preparation process, the Keping apparent resistivity continuous observation station was built in 2013 at the junction of the Southern Tianshan Mountains and Tarim Basin by the Earthquake Agency of the Xinjiang Uygur Autonomous Region. The observation system at this station has operated stably, with consistent data variations and high accuracy in both measurement channels (the NS channel and EW channel) over the past ten years. According to the sensitivity theory, our analysis demonstrates that the annual variation pattern (summer decrease/winter increase) observed in both measurement channels at Keping station is consistent with negative surface influence coefficients. Eleven earthquakes (MS≥5.0) occurred within 400km of the Keping station after 2018(aftershocks and foreshocks excluded), including two M6 and one M7 events. For qualitative analysis of the relationship between the seismogenic processes of earthquakes and the apparent resistivity variations observed at the Keping station, soil temperature and soil water content at different depths from the ERA5 assimilation datasets (ECMWF Reanalysis v5) were used to analyze the different hydrothermal condition effects on annual variation and to identify the anomalies from the background value by the interquartile range method. Our analysis of the fault virtual fault dislocation model and apparent resistivity anisotropy revealed four apparent resistivity decreases at Keping station, temporally correlated with the nucleation phases of seven M5.0+ earthquakes within a 250km radius during 2018-2024. Specifically, the rock experiment demonstrated that the resistivity of water-bearing rocks exhibits decreased variation under compressive stress. This finding is consistent with the decline changes at Keping Station, located within a compressive stress enhancement zone associated with the seismogenic process of the Wushi MS7.1 earthquake in 2024 and the Jiashi MS6.4 earthquake in 2020, respectively, revealed by the fault virtual fault dislocation model. Moreover, the anisotropic variations in apparent resistivity, as evidenced by experimental results, theoretical modeling, and seismic case studies, demonstrate a consistent pattern: the observed variation amplitude is maximized perpendicular to the direction of maximum principal compressive stress(σ1), minimized parallel to σ1, and exhibits intermediate values at oblique orientations. The focal mechanism solutions reveal that the principal compressive stress axes (P-axes) of all seven earthquakes are approximately N-S oriented, consistent with the deformation characteristics of the Keping thrust tectonic system. Furthermore, the angle between the EW channel and the principal compressive stress direction is consistently larger than that of the NS channel. Correspondingly, apparent resistivity variations in the EW direction at the Kalpin Station were consistently more pronounced than those in the NS direction, exhibiting clear anisotropic behavior. Therefore, based on the fault virtual fault dislocation model, rock physics experiment, and apparent resistivity anisotropic variation, the apparent resistivity anomalies of Keping station were proved to be associated with the seismogenic process of seven moderate earthquakes. Furthermore, simulation was carried out with reference of the electrical structure of the EW direction in Keping station, the underground medium resistivity of the EW direction in Keping station decreases by 10%, the change of apparent resistivity compared with the background value of 1.05%can be recognized, and the upper interface of the apparent resistivity change needs to rise to at least 243m above ground. Based on the electrode spacing configuration(current electrode spacing: 1 000m), this depth can be fully detected by the existing observation devices in the Keping station. This study provides both theoretical and practical support for identifying georesistivity anomalies at the Keping Station and enhancing regional seismic monitoring capabilities.

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    A STUDY ON THE DURATION OF AFTERSHOCK SEQUENCES FOLLOWING SIX LARGE EARTHQUAKES IN North China
    LIU Yue, LÜ Xiao-jian
    SEISMOLOGY AND GEOLOGY    2026, 48 (1): 142-161.   DOI: 10.3969/j.issn.0253-4967.20250097
    Abstract （464）   HTML （20）    PDF（pc） （5203KB）（240）       Save

    The duration of the aftershock sequence following large earthquakes is a crucial issue in seismicity research and is significant for seismic hazard estimation. Previous studies based on three large earthquakes that occurred since 1966 have provided important insights into aftershock activity and duration in North China. However, understanding the persistence of aftershock sequences following historical large earthquakes remains limited. In this study, we aim to comprehensively study the duration of long-lived aftershocks following large earthquake sequences in North China. Based on the modern earthquake catalog from 1970 to 2022, combined with historical earthquake records, we systematically investigate the aftershock characteristics of six large earthquakes with a magnitude of M≥7 in North China, including the 1668 Tancheng M8½, 1679 Sanhe-Pinggu M8, 1937 Heze M7.0, 1966 Xingtai MS7.2, 1975 Haicheng MS7.3, and 1976 Tangshan MS7.8 earthquakes.

    The determination of the aftershock zone is crucial in this study. We conducted a thorough review of existing research on earthquake rupture, including field investigations, fault slip inversions, and aftershocks distribution. By synthesizing these results with the seismic catalog data used in this study, we selected the aftershock zones. According to the analysis of the spatial distribution of earthquakes, temporal frequency variation, and data fitting based on the Omori-Utsu law, our study shows that the aftershocks of the six large earthquakes are still ongoing.

    The aftershock zones of the Xingtai MS7.2 and Haicheng MS7.3 earthquakes are dominated by events with magnitudes around ML≥3. In contrast, ML≥4 earthquakes at a rate of approximately 1.5 events/a from 2013 to 2022 are observed in the Tangshan MS7.8 aftershock zone. We fit the data of the Haicheng and Tangshan earthquake sequences according to the Omori-Utsu law. The p value is around 0.8, indicating a slow decaying rate. For historical earthquakes, the spatial-temporal distribution of events indicates that aftershocks are alive. In the aftershock zone of the 1668 Tancheng M8 earthquake, an average of 0.63 earthquakes/a with ML≥3.0 occurred from 2013 to 2022. Additionally, the 1679 Sanhe-Pinggu aftershocks with magnitudes ML≤2 are still active. Following the 1937 Heze M7 earthquake in Shandong Province, a MS5.9 strong aftershock occurred in 1983. The aftershock zone records an average of 1.8 earthquakes/a with ML≥2.0 during the last decade, which is higher than the rate in surrounding areas. Hence, the aftershock sequences of the Tancheng and Sanhe-Pinggu earthquakes have persisted for 354 and 343 years, respectively, and the Heze earthquake sequence has lasted for nearly 90 years.

    According to the rate-and-state friction law, we deduce that the aftershocks can last for more than 300 years with a fault slip rate less than 1mm/a. This also supports the ongoing long-lived sequences of the 1668 Tancheng and the 1679 Sanhe-Pinggu earthquakes. The tectonic loading rate in North China is slow, causing a long recurrence interval of large earthquakes, as well as the slow decaying of aftershocks.

    In all, our results indicate that aftershock sequences following M≥8 earthquakes in North China can persist for over 300 years, and the aftershock sequences of M>7 earthquakes such as the Xingtai, Haicheng, and Tangshan earthquakes, will continue for a long period. This study provides us with a further understanding of the aftershock decay in North China.

    The aftershock sequences of the Tancheng and Sanhe-Pinggu earthquakes have persisted for 354 and 343 years, respectively; the Heze earthquake sequence has lasted for nearly 90 years; and the Xingtai, Haicheng, and Tangshan regions remain seismically active with frequent small earthquakes. These findings indicate that aftershock sequences of M≥8 earthquakes in North China can persist for over 300 years, and thoses of modern large earthquakes, such as Xingtai, Haicheng, and Tangshan, will continue for a long period.

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    USING SEISMIC AMBIENT NOISE HORIZONTAL-TO-VERTICAL SPECTRAL RATIO(HVSR) METHOD TO DETECT SITE RESPONSE AND SHALLOW SEDIMENTARY STRUCTURE IN XIONG’AN AREA
    RUAN Ming-ming, LIU Qiao-xia, DUAN Yong-hong, WANG Shuai-jun, ZHENG Cheng-long, WANG Liang
    SEISMOLOGY AND GEOLOGY    2024, 46 (5): 1106-1122.   DOI: 10.3969/j.issn.0253-4967.2024.05.007
    Abstract （862）   HTML （31）    PDF（pc） （9462KB）（240）       Save

    The construction of the Xiong’an New Area is a national strategy and a long-term plan outlined by the Chinese government. To support the urban planning and development of this area, many scholars have conducted a series of geophysical surveys aimed at understanding the detailed subsurface structure. The Horizontal-to-Vertical Spectral Ratio(HVSR)method, first introduced by Nakamura, has recently gained widespread use for investigating shallow subsurface structures, site response, and microzonation.

    In this study, we utilized a large seismic array with an interstation distance ranging from 500 to 1000 meters, deployed across the Xiong’an New Area. The array consisted of over 900 short-period seismographs, covering most of the area. Using ambient-noise recordings, we removed nonrandom transient signals from the waveform data with a short-term-average over long-term-average detector automatic picking algorithm, and applied the Konno-Ohmachi algorithm to smooth the HVSR curves. For each site, we analyzed the amplitude of the peak value of the HVSR curve(A)and the corresponding frequency(f0). Both parameters were further elaborated through the creation of contour maps using the Kriging interpolation method. Additionally, the peak frequencies from the HVSR curves were used to calculate the sedimentary thickness, based on an average shear-wave velocity and the frequency-depth formula.

    The frequency map shows that the peak frequencies range between 0.6 and 1.1Hz, with an overall peak frequency of about 0.7 to 1.0Hz. The lowest frequencies were found predominantly in the vast eastern area of the study region, corresponding to geological features such as the Niubei Slope, Niutuozhen High, and Baxian Sag. According to the frequency-depth formula, a lower peak frequency indicates greater sediment depth. The variation in peak frequencies across stations highlights changes in the bedrock interface, which correspond to fault structures depicted on the geological map. Furthermore, high-amplitude areas were mainly located between the Rongxi fault and Rongdong fault, suggesting an impedance contrast between shallow and deeper layers. Stratigraphic profiles reveal that Quaternary and Tertiary sedimentary layers directly overlie the crystalline basement composed of Proterozoic metamorphic rocks. Combined analysis of peak frequency and amplitude aligns well with the available geological data. Our analysis produced 3D depth images of the Quaternary sedimentary layer interface across the study area, clearly imaging a significant seismic impedance interface at depths of 100-220m. This shallow interface corresponds to the contrast between the Tertiary rocks and the overlying Quaternary sedimentary layers. The sediment thickness progressively increases from east to west across the study area. Interfaces derived from the HVSR profiles display similar characteristics to those on the geological map and are consistent with borehole data and results from the high-density resistivity method. Moreover, we established a power-law relationship correlating the fundamental site resonance frequencies with sedimentary cover thickness obtained from borehole data in the Xiong’an New Area. The undulating characteristics of the sedimentary layers correspond closely to fault locations and geological tectonic units, confirming that faults such as the Rongxi, Rongdong, Niuxi, Niudong, and Xushui-Dacheng faults serve as boundaries for secondary geological tectonic units, influencing the structure of the near-surface sedimentary layers.

    We developed a 3D shallow subsurface sedimentary model for the Xiong’an New Area and created contour maps of amplitude(A)and peak frequency(f0). The results both support and extend previous understandings of the region’s structure. This study demonstrates that the HVSR method, in conjunction with a large seismic array, is a rapid and effective technique for investigating shallow subsurface structures and seismic site responses. The exploration of sedimentary structures and seismic site response characteristics, which are closely related to earthquake hazards, provides a critical foundation for seismic fortification and urban planning in the Xiong’an New Area.

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    LATE-QUATERNARY ACTIVITY OF THE XUSHUI SOUTH FAULT AND NIUDONG FAULT IN THE NORTH OF THE NORTH CHINA PLAIN, EVIDENCE FROM DRILLING
    HUANG Xiong-nan, YANG Xiao-ping, LIU Bao-jin, SHI Feng, ZHUANG Qi-tian, HAO Hai-jian, SHI Jin-hu, SUN Hao-yue, LU Ren-qi, HU Zong-kai, LI Kang, CAO Jun, SHU Peng, REN Guang-xue, WANG Zhen-nan
    SEISMOLOGY AND GEOLOGY    2026, 48 (1): 19-42.   DOI: 10.3969/j.issn.0253-4967.20240075
    Abstract （492）   HTML （32）    PDF（pc） （12851KB）（239）       Save

    Since the Late Pleistocene, the North China Plain, far from plate boundaries, has experienced a transformation in its geodynamic environment, with most pre-existing normal faults no longer adapting to the new tectonic stress field and thus becoming inactive. However, historical and modern earthquake catalogues indicate that the epicenters of many strong earthquakes occur near pre-existing buried normal faults on the North China Plain. There is currently a debate over whether strong earthquakes are caused by the continued activity of these pre-existing faults or by new faults.

    The Xiong'an New Area is located in the northern part of the North China Plain. Based on seismic reflection profiles and drilling studies, previous studies suggest that some pre-existing faults in this region were active into the early Quaternary but have been inactive since the Late Pleistocene. Relevant research lacked evidence from high-precision composite drilling profile investigations, making the conclusion about inactivity since the Late Pleistocene questionable. The crust-mantle structure in this area is unique, the mantle is uplifted and there is deep fluid convection along pre-existing faults, which is similar to typical intraplate seismic zones in the world, such as the New Madrid area in the United States. The epicenter of the M5¾ earthquake in 1679 was located in the study area. The determination of the latest active age of the fault is of great significance for the seismic hazard assessment of Xiong'an New Area and further research is needed. In this paper, based on shallow seismic exploration, we analyze the burial depth of the upbreakpoints of the Xushui South Fault and the Niudong Fault in the Xiong'an New Area using a composite drilling profile method, and then determine fault activity using Quaternary dating methods.

    The targeted shallow reflection seismic explorationwith survey lines laid across the Xushui South Fault and the Niudong Fault has confirmed that the upper breakpoints of the middle section of the Xushui South Fault and the eastern branch of the middle section of the Niudong Fault are both at a depth of about 80 meters or less. This result may indicate the Xushui South Fault and the Niudong Fault were active during the Late Pleistocene. Perpendicular to the projection traces of the upper breakpoints of these two faults, two composite drilling profiles were arranged with boreholes on both sides of the shallowest identified upper breakpoints. They are named as the Rongcheng drilling profile and Xiongxian drilling profile, respectively. The drilling profiles consist of 5 and 4 drill holes, respectively, and the final hole depth is approximately 150 meters for both. The average hole separations were 23.3m and 30.4m respectively.

    Based on material composition, particle size, color and consolidation degree, etc., we divided and recorded 104 and 112 units respectively for the two rows of drilling cores at the drilling site. After a comprehensive analysis, the detailed units mentioned above are reclassified and combined into 8 and 9 stratigraphic units, according to sedimentary cycles, sedimentary facies and other characteristics, and in combination with the dating results. These units cover the Holocene to the low Pleistocene series. The systematic throws of the top and bottom boundaries of the stratigraphic units and the fault zone structures preserved in the core led to the recognition of two normal faults in both the Rongcheng and Xiongxian drilling profiles. The faults in the Rongcheng profile have an up-breakpoint buried approximately 24m deep and the vertical offset of the base of the Upper Pleistocene is 15.15m. For the Xiongxian drilling line, the buried depth of the up-breakpoint of the faults is about 42m, with a vertical offset at the base of the Upper Pleistocene of 9.1m. The dating results of the samples collected near the up-breakpoints suggest that the middle segment of the Xushui South Fault and the eastern branch of the Niudong Fault were still active around approximately 20,000 years and 36,000 years ago, respectively, indicating they are Late Pleistocene faults.

    Since the Paleogene, the Xushui South Fault and the Niudong Fault have been active as bounding normal faults for the Rongcheng Uplift and the Niutuo Town Uplift, with their lower endpoints reaching depths of approximately 20 kilometers. The lithosphere beneath these faults exhibits a cold crust and a warm mantle, with a slight bulge in the upper mantle. The Xushui South Fault and the Niudong Fault serve as conduits for the ascent of deep fluids and heat. The geothermal gradient in the uplifted areas is notably higher than in the surrounding subsiding basins. Our work indicates that these faults remained active in a normal faulting mode at the end of the Late Pleistocene. Combined with previous shallow seismic exploration, it’s suggested that the Xushui South Fault and the Niudong Fault were only active in their central segments after the Late Pleistocene.

    Although the activity of these faults has diminished since the Late Quaternary, their deep-seated environment is similar to that of the New Madrid Seismic Zone in the United States, where a soft, warm upper mantle contacts a cooler, harder crust, and uneven crustal density leads to stress accumulation preferentially along pre-existing faults. Additionally, these faults act as pathways for deep fluids, which can trigger strong earthquakes.

    The continued activity of the Xushui South Fault and the Niudong Fault at the end of the Late Pleistocene is related to their deep-seated environment. Some historical strong earthquakes in the North China Plain may have been triggered by reactivation of pre-existing faults with similar characteristics.

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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 （867）   HTML （37）    PDF（pc） （11676KB）（224）       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.

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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 （699）   HTML （28）    PDF（pc） （11046KB）（221）       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.

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    SEDIMENTARY RECORDS AND SOURCE ANALYSIS OF A TSUNAMI EVENT ABOUT ~1 000 YEARS AGO IN THE PEARL RIVER ESTUARY ALONG THE COAST OF SOUTH CHINA
    WANG Wei-tao, YANG Xiao-qiang, SHU Peng, ZHANG Yu-hao, LIANG Hao, LI Lin-lin, LI Zhi-gang, WANG Da-wei, ZHANG Pei-zhen
    SEISMOLOGY AND GEOLOGY    2025, 47 (4): 999-1019.   DOI: 10.3969/j.issn.0253-4967.2025.04.20240170
    Abstract （927）   HTML （32）    PDF（pc） （7174KB）（220）       Save

    Since the Cenozoic time, the South China Sea(SCS)has formed one of the largest semi-enclosed marginal basins along the East Asian continental margin through the geological processes such as South China Sea plate rifting, seafloor spreading, and plate subduction. In the South China Sea Basin and its surrounding regions, a series of active geological structures have developed, for example, the Manila subduction zones, the Littoral(Binhai) fault zone, and the Continental Slope(Lupo) fault zone. The activity of these tectonic zones is highly prone to triggering extreme natural disasters such as earthquakes and tsunamis. Along the coastal zone of the northern part of the South China Sea(the South China continental margin), there are densely populated large cities with critical infrastructure, which are also regions severely affected by extreme natural disasters like earthquakes and tsunamis. Therefore, identifying the sedimentary records of large-scale paleotsunami events in the northern part of the South China Sea and analyzing their potential triggering mechanisms are of great significance for seismic-tsunami hazard assessment.

    This study focuses on the sedimentary strata of boreholes E15 and E12 from the Pearl River Estuary along the South China coast. Based on AMS 14C dating and a comparison of magnetic susceptibility data between boreholes E15 and E12, a high-precision chronological sequence was established for the core of borehole E15, spanning approximately the last 1000 years to the present. The core E15 is 5.9m long, with a progressively younger AMS 14C age sequence in the upper part of the core section from 4.24~0m. However, AMS 14C ages of the sediments in the lower part of core E15, from 5.9 to 4.24m, are sometimes reversed. The reversal ages may be attributed to the reworking or recycling of the sediments in the lower part of core E15.

    To reveal the depositional processes of borehole E15, we conducted detailed analyses of sedimentary grain size, sedimentary color, and geochemical elemental composition. The lower part of the core section(5.9~4.24m) for E15, consists of dark gray to grayish-black medium-to-coarse sand layers with poor sorting and contains abundant marine biodetritus. In contrast, the upper part of the core section(4.24~0m) for E15 is composed of dark gray to grayish-brown silty mud, fine sandy silt, and delicate sand layers. The upper core section exhibits finer grain size, lighter color, faint horizontal bedding, and higher terrestrial-derived elemental content, representing typical delta-shallow marine depositional environment. The lower part core section is characterized by a coarser grain size(medium to coarse) of sands, which lack clear sedimentary structures and exhibit higher offshore marine-derived elemental content, but relatively lower terrestrial-derived elemental content.

    Based on the sedimentary features and geochemical composition, the sands from 5.9~4.24m within the borehole E15 are completely different from the overlying normal, typical shallow sea-delta sediments. Considering the reversal AMS 14C ages, coarser grain size, poor sorting, darker color, higher offshore marine-derived elemental content, and lower terrestrial-derived elemental content in the lower part core of the E15, we propose that the sand layers with abundant marine biodetritus in the lower part of boreholes E15 (5.9~4.24m) may be deposits from an extreme hydrological event occurring approximately 1000 years ago. In fact, tsunami deposits dating back about 1000 years have been widely documented along the northern and western coasts of the South China Sea, the inner islands of the South China Sea, and the northwestern Philippines. Therefore, we suggest that the event deposits in the Pearl River Estuary region, along the northern part of the South China Sea, at ~1000 years ago, may also be the result of a tsunami event.

    Combining sedimentary evidence and numerical simulations, we hypothesize that a strong submarine earthquake may have occurred along the Manila subduction zone in the eastern South China Sea approximately 1000 years ago, triggering a large-scale tsunami. The medium and coarse-grained sand layers in the lower part (5.9~4.24m) of the E15 borehole within the Pearl River Estuary may be the consequence of this tsunami event.

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    THE LATE QUATERNARY ACTIVITY CHARACTERISTICS OF THE MIDDLE-NORTHERN SECTION OF THE SHANGWUJING FAULT IN THE LUXI BLOCK
    WANG Lei, REN Zhi-kun, WU Hong-bin, WANG Zhi-cai, ZHU Xiao-xiao, FU Jun-dong, JI Hao, XUE Jun-zhao, LEI Zhao-wei, WANG Ji-qiang
    SEISMOLOGY AND GEOLOGY    2026, 48 (1): 1-18.   DOI: 10.3969/j.issn.0253-4967.20250065
    Abstract （416）   HTML （49）    PDF（pc） （17021KB）（217）       Save

    Since the Middle to Late Miocene, the tectonic regime of eastern North China has undergone a significant transition from extensional deformation to a shear-dominated system under a nearly E-W compressional stress field. This shift is attributed to the combined influence of the eastward extrusion of the Tibetan plateau and the retreat of the West Pacific Plate. The Tanlu fault zone, a major active strike-slip structure in eastern China, serves as the tectonic boundary between the Luxi and Ludong blocks. Within the Luxi Uplift, located in the east part of the North China Craton, a prominent basin-and-range system has developed, controlled by a series of NW-trending faults. Late Quaternary activity along these faults, including the Cangni Fault, Xintai-Mengyin Fault, Tongyedian-Sunzu Fault, Zhangdian-Renhe Fault, Yidu Fault, and Shuangshan-Lijiazhuang Fault, demonstrates a parallel, roughly equidistant arrangement, with a convergent pattern toward the Tanlu fault zone.

    The Shangwujing Fault is a crucial NE-trending dextral strike-slip fault, and the Shuangshan-Lijiazhuang Fault is a NW-trending sinistral strike-slip fault. Spatially, these two faults form an X-shaped conjugate structure, which governs the formation and evolution of the Linqu Basin. The shallow surface expression of the Shangwujing Fault can be segmented into northern, central-northern, central-southern, and southern sections, demarcated by Tongyugou Village, Dongliushui Village, and Yiyuan Beibudong Village. While prior studies identified Late Pleistocene activity in the central-northern segment, evidence for fault motion between Jiujie Village and Dongliushui Village remained insufficient.

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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 （859）   HTML （21）    PDF（pc） （23733KB）（215）       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.

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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 （750）   HTML （24）    PDF（pc） （14562KB）（209）       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.

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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 （698）   HTML （47）    PDF（pc） （13905KB）（209）       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.

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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 （1075）   HTML （44）    PDF（pc） （9962KB）（208）       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.

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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
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    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.

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    SEIMOTECTONIC ANALYSIS OF 2023 JISHISHAN MS6.2 EARTHQUAKE IN GANSU PROVINCE
    ZHANG Bo, WANG Ai-guo, FENG Zi-wei, HE Xiao-long, ZHU Jun-wen, YAO Yun-sheng, CAI Yi-meng
    SEISMOLOGY AND GEOLOGY    2025, 47 (6): 1586-1605.   DOI: 10.3969/j.issn.0253-4967.2025.06.20240048
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    The 2023 Jishishan MS6.2 earthquake struck within the Linxia Basin along the eastern front of the Jishishan Mountains. This region is characterized by the Jishishan Fault thrusting over the Linxia Basin. However, the dip direction of the seismogenic fault remains debated, with arguments for both west- and east-dipping geometries. Faults near the epicenter include the East Margin Fault of the Jishishan Mountains(EJSF); in addition, the South Margin Fault(SLJF) and North Margin Fault(NLJF) of the Lajishan Mountains may extend southward toward the epicentral area. Active anticlines are also present. Consequently, determining whether the earthquake originated on a single fault(and which one)or involved rupture of multiple faults is an urgent and critical question. To address this, we investigated faults, mountain-basin geological sections, and earthquake-induced fissures near the epicenter. Integrating these observations with a more complete relocated earthquake catalog and five shallow-seismic profiles, we conducted a comprehensive analysis of the seismogenic fault and rupture mechanism of the 2023 Jishishan MS6.2 earthquake. The results are as follows.
    First, the faults near the epicenter include the EJSF, SLJF, and NLJF. The EJSF, situated along the eastern margin of the Jishishan Mountains, comprises multiple west-dipping reverse faults, with its most recent activity in the late Pleistocene to Holocene. The SLJF is an east-dipping reverse fault primarily north of the Yellow River and shows no discernible activity since the late Quaternary. The NLJF is a west-dipping reverse fault mainly developed north of the Yellow River; south of the river it is concealed beneath younger deposits. Its latest activity occurred primarily in the late Pleistocene.
    Second, the Jishishan-Linxia Basin section shows early Paleozoic magmatic rocks thrusting over the Linxia Group. The Linxia Group dips overall SW at 10°~20°, locally up to 29°. Near the epicenter, an asymmetric anticline deforms the Linxia Group, with a steeper eastern limb-indicative of EJSF propagation into the basin. Overlying early-Middle Pleistocene deposits display minor folding, but deformation amplitudes are markedly weaker than within the Linxia Group.
    Third, the meizoseismal zone exhibits diverse earthquake-induced fissures, including gravity, tectonic, and landslide-related fissures. Most tectonic fissures are narrow(<1cm), with maximum widths of ~5cm. They are concentrated at NWW(21%), NNW(30%), and NE(16.5%) within the EJSF's left-stepping zone, with predominant orientations matching the fault strikes. Over 50% of fissures exploit pre-existing bedrock weaknesses(faults, bedding, joints), while most others follow artificial discontinuities(e.g., road-embankment joints). Their preferential development along weak zones indicates these features result from ground shaking rather than primary fault rupture, further evidenced by mixed sinistral/dextral offsets lacking uniform sense.
    By integrating fault mapping, mountain-basin sections, and shallow-seismic profiles, we infer that both the SLJF and NLJF terminate abruptly south of the Yellow River and do not extend to the epicentral area. Only the EJSF and its associated thrust system-including blind faults and folds within the Linxia Basin-are developed near the epicenter. Analysis of relocated aftershocks from the Gansu digital seismic network, early-warning stations, and temporary arrays indicates the Jishishan earthquake likely nucleated on a blind thrust or fold branching from the EJSF. The >10km hypocentral depth greater than 10km further argues against an east-dipping back-thrust as the seismogenic source. Fault geometry and slip-rate results suggest that left-lateral slip along the West Qinling Fault transfers strain via vertical uplift along the EJSF and western Jishishan margin faults, together with crustal shortening in basins flanking the Jishishan Mountains. This strain partitioning constitutes the primary driving mechanism for the 2023 MS6.2 event.

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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
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    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.

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    SURFACE RUPTURE CHARACTERISTICS OF THE JISHISHAN MS6.2 EARTHQUAKE ON DECEMBER 18, 2023
    LI Lin-lin, JIANG Wen-liang, LI De-wen, JIAO Qi-song, LUO Yi, LI Yong-sheng, TIAN Yun-feng, LI Ying-ying
    SEISMOLOGY AND GEOLOGY    2025, 47 (4): 1058-1074.   DOI: 10.3969/j.issn.0253-4967.2025.04.20240010
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    At 23:59 on December 18, 2023, an MS6.2 earthquake struck Jishishan County, Linxia Hui Autonomous Prefecture, Gansu Province. The epicenter(35.70°N, 102.79°E) was located in the southeastern segment of the Lajishan fault zone, with a focal depth of approximately 10km. According to the Ministry of Emergency Management, the maximum intensity reached Ⅷ degree, with the NNW-striking long axis of the isoseismal zone consistent with the fault strike. Although moderate in magnitude, the earthquake has caused over 150 fatalities, primarily due to its occurrence at midnight, high population density, poor seismic resistance of housing, and secondary hazards such as debris flows.

    Following the event, a comprehensive field investigation was conducted at the epicentral area. Utilizing UAV imagery, digital surface models(DSMs) derived from GF-7 satellite data, and InSAR analysis using Sentinel-1 SAR data, the characteristics of the surface ruptures and the seismogenic structure were examined.

    The InSAR results from the ascending orbit of Sentinel-1 revealed that coseismic deformation was dominated by uplift, with a maximum line-of-sight(LOS) displacement of approximately 65mm. The primary deformation zone exhibited an elliptical shape, trending NNW, and extended approximately 10km along the fault strike—consistent with the expected rupture length for an event of this magnitude.

    Field surveys and UAV imagery identified a ~1km-long NNW-trending surface rupture east of Yinjiashan Village, which cut across multiple geomorphic units. These ruptures exhibited dominantly thrusting motion with minor right-lateral strike-slip components and were linearly distributed, indicating a tectonic origin rather than landslides or secondary processes. The maximum observed offset reached 8cm vertically and 2cm horizontally.

    Digital surface model interpretation from GF-7 imagery revealed several NNW-trending linear structures along the eastern front of the Jishishan Mountains, forming linear topographic scarps and ridges. The observed surface rupture corresponds with one of these structures(F12). Additionally, two local rivers exhibit sharp deflections toward the NNW, controlled by these structures, supporting the interpretation that they are branch faults of the northern Lajishan fault.

    According to empirical relationships between magnitude, rupture length, and displacement(Wells & Coppersmith, 1994), an MS6.2 event is expected to produce a rupture length of approximately 10km. Similar surface rupture lengths(~15km and ~11km) were observed in the 2021 MS6.1 Biru earthquake. Combined with InSAR-derived deformation extent and the lack of field coverage south of the observed rupture, it is inferred that the surface rupture may extend several kilometers southward along the same structural lineament.

    In conclusion, the seismogenic fault responsible for this event is the northern Lajishan fault, comprising multiple NNW-trending branch faults along the eastern front of the Jishishan Mountains. The surface rupture identified corresponds to one of these secondary faults. Despite of the modest scale of the Lajishan fault zone compared to major structures like the Altyn Tagh, East Kunlun, and Qilian-Haiyuan fault zones, and its lack of historical large earthquakes, this event highlights the potential seismic hazard posed by smaller faults under the influence of ongoing crustal uplift and tectonic extension in the northeastern Tibetan plateau.

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    PRELIMINARY STUDY ON LATE QUATERNARY ACTIVITY OF THE EASTERN SEGMENT OF THE NORTHERN MARGIN FAULT OF THE HAMI BASIN
    ZHAO Xue-feng, SHEN Jun, JU Guang-hong, MA Fei-peng, ZHAO Wen-gang, SONG Xu
    SEISMOLOGY AND GEOLOGY    2025, 47 (5): 1477-1493.   DOI: 10.3969/j.issn.0253-4967.2025.05.20240100
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    The fault on the northern margin of the Hami Basin is in the eastern segment of the Tianshan tectonic belt and is a deep-seated major fault that offsets the Moho discontinuity. The entire fault lies along the southern piedmont of the Barkol Mountains and the Harlik Mountains. In this study, the section of the fault along the southern piedmont of the Harlik Mountains is referred to as the eastern segment. Previous research on this fault has primarily focused on its western segment, where it has created distinct offset landforms on the surface and displaced Holocene strata, indicating activity during the Holocene. In contrast, the eastern segment of the fault is situated in the piedmont zone where the Harlik Mountains meet the Hami Basin. This area is characterized by a thin overburden, predominantly composed of coarse-grained colluvial deposits. These conditions make fault identification challenging and complicate studies of its activity. Previously, few scholars have conducted research on fault activity in this area, leading to divergent understandings regarding the precise location and activity of this fault segment. Therefore, it is necessary to employ new methods and technologies to carry out further investigation.

    This study, integrated with engineering requirements, adopted a multi-technique integrated approach with mutual validation to conduct preliminary research on this fault segment. Detailed interpretation of remote sensing imagery from the Shangmiaoergou to Bamudun Reservoir area revealed that the fault has created several scarps on the surface. However, these scarps are only distributed on older geomorphic surfaces, making it uncertain whether the fault has displaced Late Quaternary landforms. Based on remote sensing interpretation and field geological surveys, microtremor surveys were carried out. The inversion results of the microtremor data reveal a significant low-velocity anomaly zone in the shear wave velocity at the location where the fault passes, exhibiting a certain width. This indicates that the fault traverses this area, and it was observed that the fault has a relatively steep dip at depth. The microtremor inversion results successfully revealed the deep structure of the fault and validated the understanding derived from remote sensing interpretation and field investigations. To address whether the fault extends to the surface and the timing of its most recent activity, two trenches were excavated east of the microtremor survey line, and aeolian loess samples were collected for geochronological analysis to study the fault's activity preliminarily. Trench profiles and geochronological results indicate that the fault has been active since the Late Pleistocene and exhibits characteristics of multiple episodes of activity.

    Therefore, this study has obtained important evidence regarding the Late Quaternary activity of the eastern segment of the North Margin Fault in the Hami Basin, leading to the following conclusions: 1)Microtremor surveying offers advantages such as strong anti-interference capability, high efficiency, and minimal site constraints. In this study, the microtremor profiles provided the three-dimensional geometry and sectional characteristics of the fault at depth. This comprehensive multi-method approach, with mutual validation, can be highly effective for active fault detection in similar regions. 2)Geomorphological evidence for the fault's Late Quaternary activity includes the offset of the T3 terrace and alluvial fans formed during the Late Pleistocene. Fault movement has produced discontinuously distributed scarp landforms on the surface, with a total height ranging from 11 to 13m. Geochronological results also indicate that the fault has been active since the Holocene. 3)Microtremor profiles indicate a fault fracture zone width of 100m and a dip angle of 60°. Trenches and an adit were excavated on an alluvial fan, where microtremor surveys detected anomalies that exposed multiple fault planes. These fault planes generally dip northward with dip angles ranging from 35° to 54°; the dip angle is steeper at depth and becomes gentler near the surface. The phenomena revealed by the microtremor profiles are consistent with those observed in the trench and adit profiles. Furthermore, the width of the fault fracture zone measured at the adit entrance is 68m. This discrepancy arises because the microtremor-derived fracture zone includes not only the main boundary faults but also adjacent areas with reduced strength. Therefore, comprehensive analysis suggests that the width of the fault fracture zone is approximately 100m. 4)By sieving and testing loess particles within the colluvial deposits, the vertical slip rate since the Holocene is preliminarily estimated to be approximately 0.09mm/a. Integrated with regional geological data, the vertical slip rate since the mid-Late Pleistocene is inferred to be about 0.2~0.3mm/a.

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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
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    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.

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