地质力学学报

Characteristics of surface ruptures produced by recent major earthquakes on the Tibetan Plateau and its surrounding areas, and their tectonic implications

PAN Jiawei, LI Haibing, LIU Fucai, CHEVALIER Marie-Luce, LIU Dongliang, LU Haijian, CHEN Peng, YANG Shaohua

Objective Coseismic surface ruptures provide key evidence for identifying the seismogenic structures of earthquakes, elucidating crustal deformation mechanisms, and assessing seismic hazards. To understand the surface deformation and disaster development characteristics associated with different types of fault activity on the Tibetan Plateau, and to reveal the current crustal deformation patterns reflected by a series of strong earthquakes in recent years, we systematically compiled and analyzed the surface rupture characteristics of five M>6.5 earthquakes that have occurred on the Tibetan Plateau and surrounding areas since 2021, based on field surveys. Methods We used the 2021 M_W 7.4 Maduo, 2022 M_W 6.6 Menyuan, 2022 M_W 6.6 Luding, 2024 M_W 7.0 Wushi, and 2025 M_W7.1 Dingri earthquakes as representative cases. We integrated results from remote sensing interpretation, field surveys, and UAV photogrammetry, as well as seismological and geodetic data, to conduct a detailed analysis of the surface rupture and coseismic displacement distribution characteristics of these events. Results The strike-slip Maduo and Menyuan earthquakes formed coseismic surface rupture zones approximately 150~160 km and 22~31 km long, respectively, with maximum coseismic surface displacements of ~3.6 m and ~3.7 m. Contrastingly, the Luding earthquake, also a strike-slip event, exhibited a surface rupture only ~450 m long at Ertaizi. The strong, M_W 5.7 aftershock of the thrust-type Wushi earthquake generated a coseismic surface rupture zone ~5 km long with a maximum vertical displacement of ~1.7 m, while the normal-fault-type Dingri earthquake formed a coseismic surface rupture zone 25~36.5 km long with a maximum vertical displacement of ~2.7 m. Conclusions A comprehensive analysis of the spatiotemporal distribution characteristics of major regional earthquakes indicates that, prior to the 2022 Luding earthquake, major earthquakes on the Tibetan Plateau were primarily clustered around the periphery of the active Bayan Har block. The subsequent Wushi and Dingri earthquakes both occurred far from the Bayan Har block, suggesting that the clustering period of major earthquakes in this active block may have ended. Further analysis of focal mechanism solutions indicates that strike-slip earthquakes have dominated recent moderate-to-strong seismic events on the Tibetan Plateau and its periphery. This may be related to the fact that current crustal deformation on the Tibetan Plateau is primarily regulated and absorbed through the lateral extrusion of active blocks along large strike-slip fault zones. Significance The above research findings provide fundamental data and references for earthquake early warning, disaster prevention and mitigation, as well as the planning, construction, and seismic design of major regional engineering projects in the Tibetan Plateau region.

Constraining coseismic off-fault deformation of the 2022 M_W6.6 Menyuan earthquake using man-made linear markers

LIU Yulong, HAN Longfei, YAO Wenqian, LIU Jing, LI Zhenhong, SHAO Yanxiu, LIU Xiaoli, CHEN Xuan, SUN Jie, HE Liang, YIN Zilin

Objective Accurate constraints on coseismic surface displacement are essential for revealing earthquake rupture processes, assessing regional seismic hazards, and understanding the partitioning of near-surface deformation. Conventional near-field displacement measurements generally capture only localized deformation along visible rupture zones, potentially underestimating total coseismic displacement by not considering off-fault deformation. Long linear anthropogenic markers crossing rupture zones, such as pasture fences, provide a larger measurement aperture and enable us to quantify total coseismic displacement and evaluate the contribution of off-fault deformation. The 8 January 2022 M_W 6.6 Menyuan earthquake along the Haiyuan fault zone displaced multiple pasture fences across the well-preserved surface ruptures, providing an ideal opportunity to investigate total displacement and off-fault deformation. Methods In this study, we utilized unmanned aerial vehicle (UAV) photogrammetry to acquire high-resolution aerial images along the entire surface rupture zone of the 2022 Menyuan earthquake and to generate digital orthophoto maps (DOMs) and digital elevation models (DEMs) with spatial resolutions of 2–6 cm. Combined with detailed field investigations, we mapped the coseismic surface rupture at a fine scale and selected 12 groups of long, linear pasture fences crossing the rupture zone to conduct multi-aperture displacement measurements. Results The coseismic surface rupture extends for approximately 28 km and consists of two main branches: the southern branch along the Tuolaishan fault and the northern branch along the Lenglongling fault. The rupture zone was divided into four segments from west to east, namely S1 to S4, based on the geometric distribution and structural characteristics of the rupture traces, mainly NE-trending, right-stepping en echelon tensional-shear cracks, oblique compressional bulges, and mole-track-like deformation. The width of the surface rupture zone varies significantly along strike, reaching a maximum of approximately 160 m in the S3 segment. Except for the relatively wide S3, most rupture sections are mainly concentrated within a narrow width range of 10–30 m, indicating strong control by local fault geometry and rupture branching. Multi-aperture measurements using 12 groups of cross-fault pasture fences reveal that visible displacement within the mapped rupture zone ranges from 0 to 2.8 m, whereas the total coseismic displacement measured across the larger aperture of the fences ranges from 1.2 to 4.1 m. The corresponding proportion of off-fault deformation reaches 27%–76%, indicating that a substantial part of the coseismic deformation was accommodated outside the visible principal rupture traces. The maximum total coseismic displacement, approximately 4.1 ± 0.8 m, occurs in the S3 segment of the Lenglongling Fault near the epicenter, where the mean proportion of off-fault deformation is relatively low at approximately 33%. From S3 to S1 along the Tuolaishan branch westward, the total coseismic displacement gradually decreases to a mean of 1.7 ± 0.5 m, while the mean proportion of off-fault deformation increases significantly to about 55%, showing that deformation became progressively less localized and more widely distributed across the surrounding near-surface materials. Conclusions Compared with previous near-field measurements, the total coseismic displacements obtained in this study are generally larger. This discrepancy is mainly attributed to the larger measurement aperture provided by the long cross-fault fences, which enabled the capture of a more complete deformation field, including both localized displacement on the visible rupture and distributed off-fault deformation. The 2022 Menyuan earthquake produced a complex surface rupture system composed of the Tuolaishan and Lenglongling fault branches, with clear along-strike variations in rupture geometry, rupture-zone width, and displacement distribution. Multi-aperture measurements using long pasture fences indicate that off-fault deformation accounted for a considerable proportion of the total coseismic displacement, especially in the western branch rupture where deformation was more distributed. The comparison with previous near-field measurements demonstrates that relying only on localized rupture offsets may underestimate the total coseismic displacement. [Significance] This study highlights the critical importance of incorporating off-fault deformation into coseismic displacement measurements to prevent underestimating seismic slip in hazard assessments. Furthermore, it demonstrates that using long, linear, anthropogenic markers via high-resolution UAV photogrammetry is an effective, innovative approach for capturing complete near-surface deformation fields along complex strike-slip fault systems.

Liquefaction-induced large-scale ground deformation triggered by the 7 January 2025 M_S6.8 Dingri earthquake: characteristics and formation mechanisms

HUANG Ting, WU Zhonghai, HAN Shuai, LI Zhichao, FAN Fuxin, GAO Yang, TIAN Tingting, LU Shiming

Objective In liquefaction-susceptible geological settings, the spatial superimposition of earthquake-induced liquefaction and coseismic fault rupture renders the genetic attribution of surface deformation highly ambiguous, yet systematic field diagnostic criteria and a unified geomechanical framework remain elusive. Methods Integrating field emergency surveys, high-resolution remote sensing image interpretation, unmanned aerial vehicle (UAV) photogrammetry, and borehole–trench investigations with regional geological and hydrogeological context, this study systematically characterizes the spatial distribution and controlling mechanisms of large-scale surface deformation triggered by the 7 January 2025 M_S 6.8 Dingri, Tibet earthquake. Results Our results show that the extensive surface deformation along the eastern shore of Dengmecuo Lake to the Pengqu River is dominated by liquefaction-induced lateral spreading rather than coseismic tectonic surface rupture; small-scale coseismic surface ruptures occur locally along the eastern lake shore; and north of Nixiacuo, coseismic surface rupture predominates, with superimposed liquefaction deformation. The spatial extent of liquefaction-induced lateral spreading is governed by two topographic configurations: free-face conditions in river valleys, and gently sloping ground on low-gradient alluvial–lacustrine plains. Earthquake-induced liquefaction substantially reduces the shear strength of water-saturated sandy sediments and, driven by the combined effects of seismic inertia and gravity, triggers lateral spreading that generates lateral compressive forces and horizontal displacement. At the trailing edge of the deformation zone, tensional ground cracks and graben-like subsidence develop, whereas the leading edge is characterized by pressure ridges and shallow thrust structures formed by lateral compression. Tensile fissures generated by lateral spreading further provide conduits for the upward injection of liquefied sand from depth, giving rise to abundant sand volcanoes. The systematic coexistence of trailing-edge extension, leading-edge compression, and sand volcanoes constitutes a diagnostic deformation assemblage of liquefaction-induced lateral spreading, which is fundamentally distinct in geometry and kinematics from tectonic coseismic surface ruptures. The development of liquefaction deformation is jointly controlled by seismic intensity, micro-topography, the spatial distribution of liquefiable sand layers, and the depth of the shallow groundwater table. Importantly, lateral spreading can impose additional displacement onto active fault zones, and compressional liquefaction deformation may overprint fault traces, systematically biasing the identification of the geometry and kinematics of coseismic surface ruptures. Accordingly, we propose three field criteria for identifying liquefaction-induced deformation: (1) macroscopic plastic flow or fluid-like deformation features; (2) highly consistent deformation patterns along watercourses across both fault and non-fault zones under comparable depositional conditions; and (3) systematic spatial association with liquefaction indicators such as sand volcanoes. Conclusions We conclude that the large-scale deformation triggered by the 2025 Dingri earthquake should not be classified as coseismic surface rupture; rather, trailing-edge extension, leading-edge compression, and sand boils together constitute a unified lateral spreading system. Liquefaction-induced deformation exerts a pronounced overprinting effect on coseismic surface ruptures, and rigorously distinguishing the two in liquefaction-prone seismotectonic settings is essential for accurately assessing fault activity. [Significance] This study provides the first systematic mechanistic framework for liquefaction-induced large-scale deformation associated with the Dingri earthquake, and the field criteria and conceptual model established herein offer a scientific basis for seismic hazard assessment, post-earthquake reconstruction, and major engineering siting in the southern Tibetan rift system.

Symmetric and asymmetric deformation from plate-margin orogeny to intracontinental tectonics: formation mechanisms of lithospheric tectonic vergence

ZHANG Yipeng, XIE Liubiao, JIN Ruizhi, SHEN Xuzhang, HE Xiaohui, JING Hulu, LIU Kang, WANG Yang, ZHANG Peizhen

Objective Tectonic vergence records the geometric asymmetry and kinematic directionality of shortening during orogenic thickening and provides a key link between surface deformation and lithospheric-scale geodynamics. Although vergence is widely used in structural geology, its expression at the scale of entire orogenic belts remains insufficiently clarified, especially in intracontinental settings where stable plate-boundary subduction is absent. This study aims to compare vergence patterns from plate-margin orogens to intracontinental mountain belts and to identify the mechanisms controlling their formation, maintenance, weakening, and transformation. Methods We synthesize five representative orogenic systems: the Central Andes, Taiwan, the Alps, the Qilian Shan, and the Tian Shan. Surface structural styles, fold–thrust belt geometry, orogen–foreland basin coupling, geomorphic evolution, modern crustal deformation, seismicity, and lithospheric architecture — constrained by Moho/LAB geometry and geophysical imaging — are integrated to evaluate vergence at multiple scales. Results Plate-margin convergent systems commonly develop stable one-sided tectonic vergence. In the Central Andes, long-lived subduction of the Nazca slab provides persistent asymmetric forcing, causing shortening to be localized above the subduction interface and transmitted eastward toward the retroarc and foreland. The Altiplano Plateau, with crustal thickness locally reaching 60–75 km, records progressive Cenozoic crustal thickening, uplift, and eastward propagation of deformation. Taiwan, as a young arc–continent collision system, locally records early-stage bidirectional deformation around the Central Range and arc-side backthrusting near the Longitudinal Valley–Coastal Range system. However, foreland basin evolution, westward migration of the frontal fold–thrust belt, and modern shortening concentrated along the western Taiwan thrust system indicate that its long-term, orogen-scale, dominant vergence remains west-directed. The Alps demonstrate that tectonic vergence is time-dependent. During early subduction and continental collision, deformation was localized along a single subduction interface, producing a north-vergent simple-shear-dominated architecture. After collision, slab break-off, eclogitization of the orogenic root, and thermomechanical reorganization weakened the earlier interface-controlled deformation and promoted strain redistribution across both flanks of the orogen, leading to paired north- and south-vergent thrust systems and a more symmetric collisional structure. In intracontinental orogens, stable one-sided vergence is not guaranteed. The Qilian Shan and Tian Shan lack compelling evidence for a continuous, long-lived, single-sided lithospheric subduction interface. Their deformation is mainly expressed by distributed crustal thickening, high-angle reverse faulting on opposing flanks, and near-symmetric shortening. Recent studies from the Qilian Shan further show that lithospheric-scale tectonic wedges may develop along basin–mountain transition zones, where relatively rigid basin lithosphere wedges into the weakened lower crust of a thickened orogen. Such wedge structures are best interpreted as local expressions within a pure-shear, vertically coherent deformation framework rather than as large-scale simple-shear intracontinental subduction. Conclusions Lithospheric-scale tectonic vergence is controlled by the coupling among boundary conditions, negative-buoyancy forcing, and lithospheric strength–buoyancy structure. Persistent single-sided slabs or effective negative-buoyancy sources favor stable simple-shear vergence, whereas slab break-off, loss of one-sided forcing, and mechanically strong opposing blocks favor distributed pure-shear thickening and weak or near-symmetric vergence. [Significance] This study provides a unified framework for interpreting tectonic vergence from plate margins to continental interiors. It highlights vergence as a geometrically testable indicator for linking surface deformation, basin–orogen coupling, and lithospheric-scale geodynamic processes.

Advances in tectonic physical analog modeling under hypergravity

GUAN Tao, WU Lei, YANG Bo, JIA Dong, WU Xiaojun, YANG Shufeng, CHEN Hanlin

Objective Physical analog modeling is an effective laboratory method for reconstructing geological structure evolution, yet conventional normal-gravity experiments face limitations due to significant deviations in stress levels compared to natural prototypes. Hypergravity technology offers a novel pathway to address this issue and has emerged as a frontier approach for investigating deep and large-scale spatio-temporal scale Earth deformation. Methods This paper systematically reviews the research progress of hypergravity tectonic physical analog modeling, summarizes the characteristics and applications of experimental devices including small laboratory centrifuges and cantilever centrifuges used worldwide, analyzes the suitability of non-powered and powered driving systems, elaborates on the application principles of analog material systems for ductile, brittle, and complete crustal profiles, and introduces key techniques for surface deformation observation and internal structure detection. Conclusions Through the analysis of analog experiments simulating compressional structures, extensional structures, diapirs, and subduction, the unique advantages of hypergravity in amplifying density-driven effects, accelerating tectonic deformation, and improving simulation similarity are revealed, with specific patterns of its influence on structural styles and propagation processes clarified. During the research, the authors also developed a hypergravity physical analog modeling experimental chamber compatible with the Zhejiang University ZJU400 centrifuge and conducted related experimental studies. Significance This research provides a systematic reference for methodological innovation and theoretical development in hypergravity physical analog modeling, and holds positive significance for advancing structural geology toward quantification and interdisciplinary integration.

Cover Page

2026, 32(3).

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Contents

2026, 32(3): 1-2.

Abstract (40) HTML (26) PDF (386KB)(34)

2026, 32(3): 507-508. doi: 10.12090/j.issn.1006-6616.20263202

Abstract (40) HTML (16) PDF (327KB)(22)

Characteristics of surface ruptures produced by recent major earthquakes on the Tibetan Plateau and its surrounding areas, and their tectonic implications

PAN Jiawei, LI Haibing, LIU Fucai, CHEVALIER Marie-Luce, LIU Dongliang, LU Haijian, CHEN Peng, YANG Shaohua

2026, 32(3): 509-527. doi: 10.12090/j.issn.1006-6616.2026053

Abstract (168) HTML (37) PDF (22744KB)(119)

Coseismic surface rupture and seismogenic background of the 1951 M 8.0 Beng Co earthquake in the central Tibetan Plateau

LIU Fucai, PAN Jiawei, LI Haibing, CHEVALIER Marie-Luce, SUN Zhiming, JIANG Chenyi, ZHANG Siqi

2026, 32(3): 528-544. doi: 10.12090/j.issn.1006-6616.2026016

Abstract (188) HTML (45) PDF (41413KB)(116)

Study on the source characteristics and seismogenic structure of the 2021 Yangbi M_S6.4 earthquake sequence

ZHOU Minting, HE Xiaohui, LIU Zhiliang, WANG Weitao

2026, 32(3): 545-562. doi: 10.12090/j.issn.1006-6616.2025183

Abstract (158) HTML (31) PDF (11149KB)(19)

Constraining coseismic off-fault deformation of the 2022 M_W6.6 Menyuan earthquake using man-made linear markers

LIU Yulong, HAN Longfei, YAO Wenqian, LIU Jing, LI Zhenhong, SHAO Yanxiu, LIU Xiaoli, CHEN Xuan, SUN Jie, HE Liang, YIN Zilin

2026, 32(3): 563-580. doi: 10.12090/j.issn.1006-6616.2026017

Abstract (164) HTML (27) PDF (10347KB)(87)

Liquefaction-induced large-scale ground deformation triggered by the 7 January 2025 M_S6.8 Dingri earthquake: characteristics and formation mechanisms

HUANG Ting, WU Zhonghai, HAN Shuai, LI Zhichao, FAN Fuxin, GAO Yang, TIAN Tingting, LU Shiming

2026, 32(3): 581-602. doi: 10.12090/j.issn.1006-6616.2026047

Abstract (163) HTML (44) PDF (14465KB)(90)

The spatial distribution, deformation characteristics, and engineering effects of the southeastern segment of the Jiali Fault Zone

ZHU Shu, ZHANG Quan, WANG Yanbing, LI Jin, LI Renjie, HUANG Yong, LI Benliang, LIU Fucai, YAN Yuping

2026, 32(3): 603-619. doi: 10.12090/j.issn.1006-6616.2025170

Abstract (322) HTML (74) PDF (11209KB)(372)

Response of geomorphic indices to segmental activity of the Kouquan Fault on the western boundary of the Datong Basin

CHU Tianshu, REN Junjie

2026, 32(3): 620-637. doi: 10.12090/j.issn.1006-6616.2024134

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Geomorphic features and tectonic responses in the Upper Yalong River basin

TAN Ling, LIANG Mingjian, ZHANG Wei, DONG Yunxi, LIU Shao, LI Fupeng, TAN Xin, LONG Jianyu, LI Sheng

2026, 32(3): 638-655. doi: 10.12090/j.issn.1006-6616.2026003

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A 4400-year-old extreme paleo-storm surge recorded in the Dongzhai Port Chenier, Hainan Island, China

WANG Chaoqun, SUN Dongxia, ZHANG Yaoling, YANG Xiaoxiao, ZHANG Lei, HU Daogong

2026, 32(3): 656-669. doi: 10.12090/j.issn.1006-6616.2025073

Abstract (213) HTML (47) PDF (5356KB)(247)

Tectonic uplift and geomorphic evolution of the East Tianshan from the Late Cretaceous to the Cenozoic

JING Hulu, WANG Weitao, LIU Kang, LI Zhigang, ZHANG Yipeng, LU Lejun, ZHANG Peizhen

2026, 32(3): 670-682. doi: 10.12090/j.issn.1006-6616.2025177

Abstract (184) HTML (40) PDF (18968KB)(121)

Symmetric and asymmetric deformation from plate-margin orogeny to intracontinental tectonics: formation mechanisms of lithospheric tectonic vergence

ZHANG Yipeng, XIE Liubiao, JIN Ruizhi, SHEN Xuzhang, HE Xiaohui, JING Hulu, LIU Kang, WANG Yang, ZHANG Peizhen

2026, 32(3): 683-703. doi: 10.12090/j.issn.1006-6616.2026026

Abstract (145) HTML (31) PDF (17429KB)(95)

Magnetostratigraphy of the Late Cenozoic sediments of the West Kunlun foreland and its tectonic implications

ZHANG Lijuan, ZHANG Zhiliang, REN Zhikun, BAO Guodong, NING Yutao

2026, 32(3): 704-720. doi: 10.12090/j.issn.1006-6616.2025163

Abstract (164) HTML (37) PDF (8586KB)(137)

Advances in tectonic physical analog modeling under hypergravity

GUAN Tao, WU Lei, YANG Bo, JIA Dong, WU Xiaojun, YANG Shufeng, CHEN Hanlin

2026, 32(3): 721-740. doi: 10.12090/j.issn.1006-6616.2026019

Abstract (224) HTML (64) PDF (11603KB)(104)

Similarity in geomorphic physical modeling and its application to tectonic geomorphology: A review

YAN Bing

2026, 32(3): 741-758. doi: 10.12090/j.issn.1006-6616.2026015

Abstract (141) HTML (25) PDF (16437KB)(86)

The controls on the structural styles in the Wuyitage area, southwestern Tarim Basin: Insights from discrete-element numerical simulations

WANG Jinzhou, RAO Gang, DENG Xiaorui, WANG Biao, FANG Bing, LUO Qiang, XU Zhongbo, XU Chenhao

2026, 32(3): 759-770. doi: 10.12090/j.issn.1006-6616.2026037

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Structural Characteristics and Quantitative Deformation Analysis of the Central Segment of the Western Sichuan Depression

LONG Yi, WANG Renfu, DUAN Wenshen, kong xuanlin, DING Yunan, wang chun, zhou xiaorong, QIU Jianhua

doi: 10.12090/j.issn.1006-6616.2026042

[Abstract](50) [PDF 4729KB](37)

Abstract:
The central segment of the Western Sichuan Depression, located on the western margin of the Sichuan Basin, has been influenced by the Longmen Shan orogenic belt and has experienced multiple phases of tectonic movement and superimposed modification, resulting in the formation of a complex deep-shallow dual-layer structural system. Based on high-precision three-dimensional seismic data from the central segment of the Western Sichuan Depression, this study conducts fine structural interpretation, selects profiles of typical buried detachment anticlines, and applies the area-depth-strain (ADS) method to perform quantitative analysis of multi-phase structural deformation. In combination with regional structural deformation characteristics, it systematically investigates the structural deformation mechanisms and basin-mountain coupling processes in the central segment of the Western Sichuan Depression. The results show that, bounded by the Middle-Lower Triassic gypsum-salt detachment layer, the central segment of the Western Sichuan Depression is vertically decoupled into a shallow frontal thrust-nappe system in the piedmont and a deep buried detachment deformation system within the basin. The structural deformation in the study area exhibits a segmented pattern along strike, with deep deformation weakening from south to north and shallow deformation strengthening from south to north. This segmentation results from the combined effects of heterogeneous compression of the orogenic belt, differences in basement structure, and spatial variations in the detachment layer. Combined with the ADS quantitative analysis results of detachment anticlines, this study suggests that the multi-phase deformation of detachment anticlines in the central segment of the Western Sichuan Depression displays a pulsed distribution pattern of “early Indosinian deep-level initiation (217 m), middle Indosinian shallow-level dominance (142 m), and late Indosinian overall waning (≤31 m)”, quantitatively revealing an episodic pattern in which the basin-mountain compressional deformation was transferred from deep to shallow levels and from early to late stages. Meanwhile, the differences in shortening amounts between the deep and shallow deformation systems in anticlines A and B indicate a “staggered peak” response over time: the deep deformation system experienced significant shortening during the early Indosinian (anticline B shortening of 217 m), whereas the shallow deformation system responded most strongly to compression during the middle Indosinian (Anxian Movement), together forming a unique coupling style of “deep pre-existing folding–shallow thrust nappe”. The “vertical layering–lateral segmentation–multi-phase quantification” structural understanding system established in this study not only provides a quantitative structural basis for deep to ultra-deep petroleum exploration in foreland basins, but is also of great significance for deepening the understanding of the basin-mountain coupling processes in the central segment of the Western Sichuan Depression.

Paleomagnetic constraints on a two-stage Cenozoic tectonic framework of the South China Block and the southeastern Tibetan Plateau

LIAO Yilian, HUANG Baochun, WANG Jianhua, LU Hongliang, SUN Qishun, CHEN Zaixu

doi: 10.12090/j.issn.1006-6616.2025181

[Abstract](98) [PDF 0KB](0)

Abstract:
[Objective] The kinematic history of the South China Block (SCB) following the breakup of Gondwana is of critical significance for constraining the timing of the initial opening of the Ailao Shan–Song Ma Paleo-Tethys Ocean basin. However, the understanding of this process has been limited by the scarcity of reliable paleomagnetic data. [Methods] In this study, systematic paleomagnetic, rock magnetic, and petrographic analyses were conducted on red beds and limestones of the Upper Silurian Kuanti Formation from the Qujing area, Yunnan Province. [Results] The samples were, however, very likely remagnetized during the Cenozoic. Rock magnetic analyses indicate that the red beds are predominated by hematite as the primary carrier of magnetization, with minor contributions possibly from magnetite/titanomagnetite. Anisotropy of magnetic susceptibility (AMS) results reveal combined features of sedimentary, incipient deformation and strong cleavage fabrics, suggesting that the sediments may have undergone significant syn-depositional or post-depositional tectonic deformation. Lithological observations indicate that the magnetic minerals within both the red beds and limestones are primarily authigenic. From 14 sites (85 red bed and limestone specimens), a stable, high-temperature or high-field characteristic remanent magnetization (ChRM) component, converging towards the origin, was isolated, yielding a mean direction of Declination (D_g)= 332.2°, Inclination (I_g)= 51.6°, precision parameter (k_g)= 19.0, confidence cone half-angle of the mean direction (α₉₅)= 9.4° before and of Declination (D_s)= 342.5°, Inclination (I_s)= 25.7°, precision parameter (k_s)= 15.8, confidence cone half-angle of the mean direction (α₉₅) = 10.3° after the tilt-adjustment. Several fold tests indicate a negative result. The corresponding paleomagnetic pole calculated from the in-situ ChRM direction is located at 64.9°N, 35.2°E (A₉₅=7.9°). This paleomagnetic pole is consistent with reference poles for the SCB between 20~5 Ma, suggesting that the Kuanti Formation underwent remagnetization at approximately 20 Ma. [Conclusion] Integrating these results with previously reported reliable paleomagnetic data from small blocks within the southeastern Tibetan Plateau and the SCB since 50 Ma, as well as prior studies on the tectonic evolution of the southeastern Tibetan Plateau, a two-stage model of co-evolution between the SCB and the southeastern Tibetan Plateau is proposed. During 50~20 Ma, collision between the Indian and Eurasian plates resulted in the uplift and crustal shortening of the southeastern Tibetan Plateau. The fault systems along the southeastern Tibetan Plateau exhibited left-lateral strike-slip motion, which induced clockwise rotation of the SCB relative to stable Eurasia. The amount of clockwise rotation varied across different locations of the SCB, with sites closer to the southeastern Tibetan Plateau fault systems experiencing larger rotations. Since 20 Ma, continuous northward subduction of the Indian Plate beneath Eurasia, combined with multiple dynamic processes, including lower to middle crustal flow, gravitational spreading, mantle convection inducing by the tearing of the Indian Plate, and Pacific–Indian Ocean subduction, has driven clockwise rotation and extrusion of the southeastern Tibetan Plateau. During this stage, the fault systems exhibit right-lateral strike-slip motion, while the SCB underwent counterclockwise rotation relative to stable Eurasia. The magnitude of rotation is generally consistent across different locations. [Significance] Therefore, the transition of the SCB from a “clockwise rotation” to a “counterclockwise rotation” behavior essentially represents a direct manifestation of the shift in the geodynamic regime along the southeastern Tibetan Plateau from vertical uplift to tectonic extrusion. The ~20 Ma paleomagnetic data in this study provide robust evidence for a regional reversal of the tectonic framework along the southeastern Tibetan Plateau.

Formation and destruction of the Minle Basin in the Hexi Corridor: insights into Cretaceous tectonic characteristics of the northeastern Qinghai-Tibetan Plateau

Adina Alimu, ZHANG Beihang, YANG Yan, ZHAO Heng, JIANG Hai, LIU Yugang, DING Zhe

doi: 10.12090/j.issn.1006-6616.2025154

[Abstract](80) [PDF 8224KB](44)

Abstract:

[Objective] A series of sedimentary basins developed in the Hexi corridor along the northeastern margin of the Qinghai-Tibetan Plateau during the Early Cretaceous. These basins preserve critical records of pre-Cenozoic tectonic evolution in this region, forming the basis for understanding the growth mechanism of the Qinghai-Tibetan Plateau during the Cenozoic. However, the nature of these Early Cretaceous basins remains controversial, hindering consensus on late Mesozoic tectonics in this critical area. [Methods] This study focuses on the Minle Basin in the central Hexi Corridor and carried out a detailed field structural investigation in this area. Through structural analysis and paleo-stress reconstruction, the formation and destruction process of the Minle Basin was redefined. [Results] Our investigation reveals that Lower Cretaceous strata in the Minle Basin contain numerous syn-sedimentary normal faults that strike initially nearly north-south, indicating that the Minle Basin was a fault-bounded extensional basin controlled by nearly east-west extension during the Early Cretaceous. Subsequent deformation is recorded by NE-SW- and NW-SE-trending folds, coupled with shortening structures in Lower Cretaceous strata, indicating NE-SW- and NW-SE-trending horizontal shortening events during the Late Cretaceous. [Conclusion] The Early Cretaceous extension of the Minle Basin was consistent with the widespread extensional deformation and extensional stress direction across East Asia during this period, which was a product of the retreat of the Paleo-Pacific Plate and the consequent mantle material flow. The bidirectional shortening during the Late Cretaceous resulted from the superimposition of the remote effects of simultaneous compression events that developed in the Tethys tectonic domain along the southern margin of the Eurasian Plate and the Pacific tectonic domain along the eastern margin of the Eurasian Plate. [Significance] The deformation mentioned above indicates that the influence of the subduction of the Paleo-Pacific Plate extended westward at least as far as the Hexi Corridor and the northern Qinghai-Tibetan Plateau.

Numerical simulation analysis of seismically triggered load and ball-and-pillow structures in the lacustrine sediment

yan zelong, FAN Ruixiang, ZHANG Junjie, ZHONG Ning, LIANG Lianji

doi: 10.12090/j.issn.1006-6616.2026005

[Abstract](83) [PDF 1204KB](53)

Abstract:
[Objective] Seismically triggered soft-sediment deformation structures (SSDSs) in the lacustrine sediments serve as reliable stratigraphic records for studying paleoearthquake events in tectonically active regions. Load and ball-and-pillow structures, as one of the common types of SSDSs, are often attributed to reverse density gradients between different sedimentary layers driven by gravity. However, the formation processes and mechanisms of these structures, as well as their quantitative relationship with seismic intensity remain unclear. [Methods] This study employs a FLUENT software to simulate the formation processes of load and ball-and-pillow structures in saturated sand-clay sedimentary layers with varying physical properties (density, dynamic viscosity and thicknesses) under different seismic accelerations (0.125g, 0.25g, 0.5g, and 0.8g). [Results] The results indicate that as the seismic accelerations increases, load and flame structures appear earlier and gradually evolve from small-scale load structures to larger-scale ones and ball-and-pillow structure. Under the same seismic acceleration, a larger density and dynamic viscosity difference, and a larger thickness in sand layer would result in more intense and large-scale load and ball-and-pillow structures. [Conclusions] The simulation results are generally consistent with the morphological characteristics of load and ball-and-pillow structures identified in the field investigation in the Tashkorgan area. [Significance] This finding verifies the seismic trigger of SSDSs in this region and provides a new technological insight into the study of SSDSs and paleoearthquakes.

Remote Sensing Image Characteristics and Seismic Hazard of the Baiganhu Fault on the South Side of the Central Segment of the Altyn Tagh Fault

LIU Hanlin, YUAN Zhaode, CHEN Tao

doi: 10.12090/j.issn.1006-6616.2025187

[Abstract](73) [PDF 4759KB](48)

Abstract:
[Objective]Accurately defining the spatial distribution and scale of active faults is fundamental for for analyzing regional tectonic deformation and assessing seismic hazards. [Methods]Using multi-source high-resolution satellite imagery, this study systematically interprets the faulted geomorphic features of the sinistral strike-slip Baiganhu Fault, located south of the central segment of the Altyn Tagh Fault. [Result]The results show that the fault is approximately 247 km long with a general NEE trend. It has been intensely active since the Late Quaternary, as evidenced by extensively developed faulted geomorphic markers such as offset alluvial fans, transtensional cracks, pressure ridges (mole tracks), offset gullies, and sag ponds. Based on its geometric structure and spatial distribution, the Baiganhu Fault can be divided into western, central, and eastern segments. The central segment preserves a ~50 km long surface rupture zone with an average coseismic horizontal offset of 4.8 m, indicating the occurrence of a past strong earthquake with M_W 7.4±0.3. Statistical analysis of 99 left-laterally offset gullies shows an average horizontal offset of 4.3-4.8 m for the most recent event. [Conclusions]While a throughgoing rupture of the entire Baiganhu Fault could generate an earthquake of M_W 7.8±0.3, the ~5 km wide stepover it forms with the Altyn Tagh Fault is unlikely to fully arrest throughgoing rupture propagation. [Significance]This implies a potential for cascading rupture between the two faults. Therefore, the seismic hazard posed by the Baiganhu Fault warrants significant attention, and regional seismic hazard assessments must fully consider the possibility of its cascading rupture with the Altyn Tagh Fault.

Permian-Triassic reservoir characteristics and differential origins in the Pen-1 West Sag

ZHANG Fushun

doi: 10.12090/j.issn.1006-6616.2026027

[Abstract](88) [PDF 3365KB](57)

Abstract:
[Objective] The Pen-1 West Sag is an important replacement area for hydrocarbon exploration in the hinterland of the Junggar Basin. However, systematic studies on the characteristics and formation mechanisms of its deep to ultra-deep Permian–Triassic reservoirs remain relatively weak. [Methods] This study comprehensively utilizes core, logging, analytical testing, and seismic data to systematically investigate the petrology, physical properties, pore structure, and diagenetic evolution characteristics of the Permian–Triassic reservoirs in this sag, and reveals the main controlling factors for reservoir quality differences. [Results] The results show that the reservoirs are predominantly lithic sandstones, with volcanic lithic fragments averaging over 80%, among which intermediate–basic extrusive rock fragments dominate. The reservoir physical properties vary significantly vertically: the Karamay Formation and Baikouquan Formation have the best physical properties, with porosity mainly ranging from 5% to 13% and permeability mostly concentrated between 0.1 mD and 10 mD, belonging to relatively high-quality reservoirs, while the Upper Urho Formation and Lower Urho Formation have poorer physical properties. The reservoir pores are dominated by secondary pores, among which dissolution pores of zeolite cements and intragranular dissolution pores of volcanic lithic fragments are the most developed. [Conclusions] Statistics show that secondary pores account for more than 70% of the total pore space in the Baikouquan Formation and Upper Urho Formation, whereas in the Karamay Formation, secondary pores account for about 40%–60%, and residual primary intergranular pores still occupy an important position. The differences in reservoir physical properties are jointly controlled by multiple factors, including provenance characteristics, lithology (grain size), diagenetic alteration (coating development, zeolite cementation and dissolution, clay filling), composition of volcanic lithic fragments, and temperature–pressure field conditions. Based on the analysis of diagenetic evolution sequences and the differences in reservoir pore type proportions, two types of reservoir physical property evolution models are proposed: the primary pore-preserved type (represented by the Karamay Formation) and the secondary pore-dominated type (represented by the Baikouquan Formation and Upper Urho Formation). [Significance] This understanding provides an important basis for the prediction and evaluation of deep clastic reservoirs in the Pen-1 West Sag and similar geological settings.

Study on the cooling history of Pliocene basalt columns in Kanchanaburi，Thailand

ZHOU Enxiong, YAN Yonggang, LAI Zhenyang, LI Danxin, FU Yalan, DENG Xiaotai, ANCHANA Thanakan, VEERAVINANTANAKUL Apivut, CHARUSIRI Punya, WANG Weitao, HUANG Baochun, ZHANG Peizhen

doi: 10.12090/j.issn.1006-6616.2025169

[Abstract](132) [PDF 5062KB](101)

Abstract:
[Objective] Columnar joints in basalt are typical structures formed during magmatic cooling and contraction. However, their formation mechanisms, internal structures, and cooling histories remain debated. This study aims to constrain the internal structure and cooling history of large basalt columns using integrated rock magnetic and paleomagnetic methods. [Methods] Detailed rock magnetic and paleomagnetic analyses were conducted on 49 oriented samples collected from two Pliocene basalt columns (up to 1.5 m in diameter) in the Bo Phloi section, Kanchanaburi, Thailand. Rock magnetic experiments include hysteresis loops, isothermal remanent magnetization (IRM) acquisition, first-order reversal curve (FORC) analysis, anisotropy of magnetic susceptibility (AMS), and temperature-dependent magnetic susceptibility measurements. Stepwise thermal demagnetization was used to isolate stable remanent magnetization components. [Results] Hysteresis loops and IRM acquisition curves show saturation below ~300 mT and a two-stage increase with increasing field, indicating contributions from magnetic components with different coercivities. FORC diagrams confirm pseudo-single-domain (PSD)-dominated magnetic domain states, with systematic differences between column margins and interiors. AMS results show that both basalt columns are characterized by sub-vertical minimum susceptibility axes (K₃) and sub-horizontal maximum (K₁) and intermediate (K₂) axes, with generally low anisotropy degrees (Pj < 1.05), indicating a primary near-horizontal magma flow fabric during emplacement and no evidence for vertical melt migration or internal convection. AMS parameters further reveal systematic spatial variations: marginal samples exhibit lower magnetic susceptibility (Km), lineation (L), and anisotropy degree (Pj), with predominantly oblate fabrics (T > 0), whereas interior samples show higher Km, L, and Pj values and predominantly prolate fabrics (T < 0). These differences reflect contrasting cooling conditions, with rapid cooling at the margins and slower cooling in the interiors. During magma solidification, the margins of the basalt columns experienced faster cooling, resulting in shorter time available for crystallization and preferred orientation of magnetic minerals, and consequently lower magnetic susceptibility and anisotropy. In contrast, the interior portions cooled more slowly and likely remained in a high-temperature plastic or partially molten state for a longer period, allowing magnetic minerals to crystallize more completely, become concentrated, and align under thermal contraction stress. Paleomagnetic results indicate that thermal demagnetization isolates stable single-component remanence carried by PSD titanomagnetite. Six marginal samples from basalt column A exhibit more scattered virtual geomagnetic pole (VGP) distributions and anomalous directions, whereas the remaining 43 samples show relatively clustered VGPs after tilt correction. Systematic variations in remanent magnetization directions and VGPs indicate that cooling did not proceed symmetrically or uniformly from the margins toward the cores, but rather followed an asymmetric, unidirectional regional cooling pattern, which was likely influenced by a localized heat source. [Conclusions] Based on integrated rock magnetic and paleomagnetic analyses, the main conclusions are summarized as follows. (1) The basalt columns from Kanchanaburi are dominated by pseudo-single-domain (PSD) titanomagnetite, and AMS fabrics with sub-vertical K₃ and sub-horizontal K₁ and K₂ axes indicate a primary near-horizontal magma flow during emplacement. (2) Marginal zones cooled faster, producing finer magnetic grains, lower anisotropy, and oblate fabrics, whereas interior zones cooled more slowly, allowing stronger magnetic alignment and higher anisotropy with predominantly prolate fabrics. (3) Systematic variations in paleomagnetic directions and VGPs from 49 samples indicate that post-jointing cooling was not uniform or symmetric, but instead proceeded as an asymmetric, unidirectional process across the basalt columns. [Significance] This study contributes to a better understanding of the cooling process of basaltic lava and provides new insights into geomagnetic secular variation.

A Study of Diffusion Coefficients and Multi-scale Diffusion Models for Oil and Gas Transport in Shale

ZHANG Mingdi

doi: 10.12090/j.issn.1006-6616.2025140

[Abstract](155) [PDF 794KB](94)

Abstract:
[Objective] Diffusion governs fluid transport and production behavior in shale oil and gas reservoirs with nano–microscale pore–fracture systems. However, strong nanoscale confinement and multiscale structural complexity make the underlying mechanisms unclear, and existing models lack cross-scale predictive capability. This study aims to clarify diffusion mechanisms and develop a model applicable to multiscale porous media. [Methods] High-temperature and high-pressure diffusion experiments were conducted, combined with fractal modeling and nanoscale confinement analysis. A fractal–confinement diffusion model was established and validated against experimental data. [Results] Nanoscale confinement significantly affects phase behavior and diffusion capacity. (1) Confinement induces phase-diagram contraction and a leftward shift of the critical point, leading to a reduction of effective diffusivity by approximately five orders of magnitude compared with bulk fluids. (2) Porosity and permeability are the primary structural controls. When porosity increases from 5.68% to 10.53%, diffusion coefficients increase by about one order of magnitude. When bedding-fracture permeability increases from 1.69 mD to 404.88 mD, diffusion coefficients rise by 3–4 times, indicating enhanced transport pathways. (3) Pressure and temperature exert different effects: increasing pressure (10–36 MPa) suppresses gas-phase diffusion but promotes liquid-phase diffusion, whereas increasing temperature (80–115 °C) enhances diffusion for both phases. (4) Diffusion capacity in fractures exceeds that in the matrix by 1–2 orders of magnitude, demonstrating the dominant role of fractures in large-scale transport. (5) The proposed model matches experimental results well and captures multiscale diffusion behavior, enabling structural sensitivity analysis and cross-scale prediction. [Conclusions] Diffusion in shale reservoirs is jointly controlled by nanoscale confinement, pore–fracture structure, and thermodynamic conditions. Confinement reduces diffusivity and alters phase behavior, while fractures significantly enhance transport capacity. The proposed model effectively integrates these effects and provides accurate cross-scale predictions. [Significance] This study establishes a practical framework for modeling shale-fluid diffusion and provides theoretical support for quantitative evaluation of fluid transport and optimization of reservoir development.

Reactivation Mechanism and Stability Trend Prediction of the Huangci 2# Landslide

DOU Xiaodong, LI Yushan, MENG Yateng, CONG Kai, ZHANG Yongjun, JIA Qiang

doi: 10.12090/j.issn.1006-6616.2026014

[Abstract](290) [PDF 2310KB](228)

Abstract:
[Objective] To investigate the disaster-causing mechanism, dynamic evolution process, and post-disaster stability trend of the reactivation of the Huangci No. 2 landslide in Heifangtai, Gansu Province on December 10, 2025. [Methods] Field surveys and the Transient Electromagnetic Method (TEM) were comprehensively applied to analyze the deep structure of the landslide. A back-analysis was conducted based on Massflow numerical simulation, and the 3D limit equilibrium method was utilized to perform quantitative stability evaluation for the post-disaster deposit and the high-steep rear wall. [Results] (1) The landslide reactivation is the result of toe excavation, long-term irrigation, and special meteorological conditions. The freezing-induced water retention effect acted as the direct trigger, where surface freezing blocked seepage channels, causing an accumulation of pore water pressure and inducing a loess-mudstone bedding slide. (2) The entire sliding process lasted for 22 hous, with a cumulative displacement of 310 m. The Massflow analysis reproduced the four-stage evolution process of "creep-acceleration-deceleration-consolidation", and the IoU of the deposition morphology reached 85.85%. (3) Quantitative calculations shows that the current deposit has a safety factor greater than 1.15, indicating a stable state of settlement and consolidation; however, under extreme saturation conditions, the potential collapse volume of the high-steep rear wall could reach 40.9×10⁴ m³, with a maximum sliding distance of approximately 640 m. [Conclusion] The analysis suggests that the reactivation of the landslide is controlled by freezing-retained water and multiple disturbance mechanisms. Although the main body has currently stabilized, secondary instability of the high-steep rear wall is highly likely to occur, necessitating the establishment of a long-term dynamic monitoring system to strictly prevent high-position disasters. [Significance] The understanding of the reactivation mechanisms of loess landslides in seasonal freeze-thaw zones was deepens, providing a scientific basis and technical support for prevention and mitigation of such landslides.

Tectonic evolution of the WesternYangtze Block during the Ediacaran–Cambrian: Evidence from detrital zircon U-Pbgeochronology

Zhiqiang SHI, Le SUN, ZHANG Hong, PEI Jinyun, LI Wei

doi: 10.12090/j.issn.1006-6616.2025065

[Abstract](174) [PDF 2116KB](208)

Abstract:
[Objective] The Yangtze Block was a crucial component of the Gondwana supercontinent. During the Ediacaran-early Cambrian, its western margin underwent a marked transition from carbonate-dominated to siliciclastic-dominated depositional environments. However, the tectonic dynamics controlling this sedimentary facies shift of early Cambrian sedimentation remain poorly constrained. The exposed thick Early Cambrian terrigenous clastic rocks on the western Yangtze Block are key archives for tracing sediment sources and studying the geotectonic background of the Early Cambrian .[Method] This study carried out systematic detrital zircon U-Pb geochronology and whole-rock element analysis on the lower Cambrian Qiongzhusi Formation on the western Yangtze Block to study above question. [Results] The results indicate: (1) The clastic rocks exhibit high-field-strength elements (HFSEs) and large-ion lithophile elements (LILEs; e.g., Th, Zr, Hf, Ba, Pb) consistent with upper crustal compositions, whereas Sr, Sc, V, Cr, Cu, Ni, and Zn show depletion relative to upper continental crust (UCC)-particularly pronounced for Sr, Cr, V, and Cu. The immobile elements (Th, Sc, Hf, Zr, Ho) and rare earth elements (RREEs; e.g, La, Ce, Yb) suggest a dominantly felsic igneous provenance of the upper continental crust; (2) Primary age clusters of detrital zircon U-Pb ages in the Qiongzhusi Formation are ca.590-500Ma and ca.880-720 Ma, with subordinate groups at 1900-1500 Ma and 2500-2400 Ma. [Conclusions]Integrated with regional data and prior studies, we propose that the early Cambrian detritus was largely derived from the Ediacaran-Early Cambrian magmatic rocks in the Longmenshan tectonic belt (Ediacaran-early Cambrian), and the late Neoproterozoic felsic magmatic rocks of the Panxi-Hannan magmatic arc, Ailaoshan Magmatic Arc and the Jiangnan Orogen. The Proto-Tethyan Ocean's subduction beneath the western Yangtze during the Ediacaran-early Cambrian converted the western Yangtze from a passive to an active continental margin, and formed a late Ediacaran-early Cambrian magmatic arc. This arc supplied voluminous early Cambrian detritus, ultimately shifting the western Yangtze margin to a siliciclastic-dominated depositional system. [Significance]These findings reveal the provenance linkages between the western Yangtze and adjacent orogenic belts, thereby providing critical constraints for reconstructing the tectonic and paleogeographic evolution of the South China Block during the Ediacaran-Early Cambrian.

Evaluation of Source Rocks and Oil Source Correlation in Chang 7-Chang 6 Member of Yanchang Formation in Jingbian Area, Ordos Basin

SiWei TANG, Hui XUE, YouJun TANG, ShuMin WANG, GuangMing HU, Geng LI, FangTingYu SHI

doi: 10.12090/j.issn.1006-6616.2025050

[Abstract](188) [PDF 2632KB](239)

Abstract:
Objective The Chang 7 and Chang 6 Members of the Yanchang Formation in the Jingbian Area of the Ordos Basin constitute significant source rock intervals. However, systematic studies on their hydrocarbon generation potential and contributions to petroleum accumulation remain limited, which constrains further exploration efforts in this region. Therefore, this study integrates geochemical analytical methods to systematically characterize the distribution and the geochemical properties of the Chang 7 and Chang 6 source rocks in the Jingbian area, as well as the geochemical signatures of the crude oils from the Yan 9 and Chang 2 reservoirs in the Jingbian Oilfield. Methods By comparing the geochemical parameters between the local Chang 6 and Chang 7 source rocks and the Zhangjiatan Shale in the center of the basin, the potential sources of the oils in the Yan 9 and Chang 2 reservoirs were identified. Results The results demonstrate that the Chang 7 source rocks are high quality, with widespread distribution and considerable thickness. They are characterized by Type I-II₂ kerogen and are in the mature stage. The biomarker characteristics indicate mixed organic matter inputs, deposited in a reducing environment with low salinity. The low Pr/Ph and high C₂₇/C₂₉ regular sterane ratios further suggest that the organic matter is predominantly derived from aquatic algae and other lower organisms, consistent with a reducing, fresh to brackish water depositional environment. In contrast, the Chang 6 source rocks are of medium to high quality, containing Type II₂-III kerogen and are generally in the low-to-mature stage. The moderate Pr/Ph and low C₂₇/C₂₉ regular sterane ratios reflect a predominance of terrigenous higher plant input, deposited under a weakly reducing environment. The oil-source correlation results reveal that the Yan 9 and Chang 2 oils are of the same origin, primarily derived from the Chang 7 source rocks, with a minor contribution from the Chang 6 Member. Conclusion (1) the Chang 7 Member is the primary, high-quality source rock in the Jingbian area, superior to the Chang 6 Member in terms of thickness, lateral distribution, organic richness, and hydrocarbon generation potential. (2) Distinct biomarker signatures differentiate the Chang 7 (aquatic/algal, reducing), Chang 6 (terrigenous, weakly reducing), and distal Zhangjiatan (highly aquatic, strongly reducing) source rocks. (3) The Yan 9 and Chang 2 crude oils share a common origin and are primarily sourced from the local Chang 7 source rocks, with a possible minor contribution from the Chang 6 Member. The oils show no direct genetic link to the Zhangjiatan Shale in the basin center, supporting a predominantly local hydrocarbon sourcing model for the Jingbian area. Significance This study provides crucial geochemical evidence for a local hydrocarbon system within the Jingbian area, resolving previous ambiguities regarding oil sources and assessing the resource potential in the Jingbian Area, Ordos Basin.

Research on mechanical parameter prediction and modeling methods based on statistical regression and prestack inversion—Taking a particular area in the Bonan Depression as an example

Bin WANG, Han XIAO, XueMin NIU, RuiXuan ZHANG, Xing GE

doi: 10.12090/j.issn.1006-6616.2025084

[Abstract](214) [PDF 1153KB](317)

Abstract:
Abstract: [Objective] In the development of unconventional oil and gas, there exist problems such as complex reservoir structure and unclear rock mechanical properties. During the design of horizontal well trajectories and fracturing schemes, it is necessary to rely on rock mechanical models for segment and cluster division and design, thereby increasing the modification volume, reducing the risk of set changes, and achieving efficient development of unconventional oil and gas. The rock mechanics model can simultaneously reflect the continuous changes of mechanical parameters in the longitudinal and transverse directions with high resolution in the target area of the horizontal well trajectory. Therefore, in response to the model requirements, this paper provides a mechanical parameter prediction and modeling method based on statistical regression and prestack inversion. [Methods] Basing on the core test data and logging data, the quantitative relationship between elastic parameters and rock mechanical parameters is established and analyzed. Then, three-dimensional prestack inversion is performed using both drilling data and seismic data to obtain precise elastic parameters, including longitudinal wave velocity, density, Poisson's ratio, and Young's modulus. [Results] The application of this method in the tight glutenite reservoirs of the Bonan Sag has yielded significant and practical results. First, a robust quantitative relationship between mechanical and elastic parameters was established. The statistical regression relationship between Young's modulus and Uniaxial Compressive Strength (UCS) demonstrated a strong correlation (e.g., R² > 0.75), validating the feasibility of predicting rock mechanical strength from elastic parameters in this glutenite formation. Statistical analysis confirmed that the mechanical parameters of these highly compacted, low-porosity glutenites are primarily controlled by lithology and gravel content, exhibiting a very weak correlation with burial depth. This justifies the use of a unified predictive model across the entire studied depth interval. Second, a high-resolution 3D mechanical parameter model was constructed. A depth-domain structural model was built using logging data and a smoothed time-depth velocity field. Following attribute extraction, a comprehensive 3D mechanical parameter model for the target block was established. This model effectively overcomes the discreteness and non-continuity inherent in core and logging data, accurately characterizing the continuous lateral and vertical variations of mechanical properties. Third, the results are directed toward engineering application. To fully leverage the high vertical and lateral resolution of the mechanical parameter volume, the calculated seismic attributes were integrated into the 3D geological model based on engineering requirements. This outcome provides an accurate model for fracturing design, enabling precise assessment of the rock mechanical distribution along horizontal well sections, rational design of stage and cluster placement, optimization of pumping parameters, and enhancement of fracture conductivity. Consequently, it significantly increases the stimulated reservoir volume, effectively boosting single-well productivity and recovery rates. [Conclusion] The study leads to the following main conclusions: The integrated methodology of pre-stack inversion and statistical regression is a viable and effective solution for predicting 3D mechanical parameters in tight glutenite reservoirs. This method builds a bridge between petrophysical and seismological parameters, effectively resolving the challenge of poorly constrained rock mechanical properties in complex unconventional reservoirs. The constructed 3D mechanical parameter model provides a more reliable geological basis for optimizing well trajectories and fracturing designs. [Significance] The primary significance of this research lies in providing a reliable and scalable method for 3D rock mechanical parameter prediction and modeling, possessing substantial theoretical innovation and practical application value. It offers a dependable data foundation and a theoretical framework for defining mechanical boundaries and optimizing fracturing designs in heterogeneous tight reservoirs. This approach holds significant potential for improving fracturing efficiency and maximizing production in challenging tight glutenite formations.

MA Zhanrong, LI ZhenHong, LIU JianPing, HU AiPing, LinLin KOU

doi: 10.12090/j.issn.1006-6616.2025031

[Abstract](161) [PDF 3282KB](322)

Abstract:
[Objective] The dolomite of Ordos basin west margin complex tectonic belt Ordovician Kelimoli Formation as a high quality reservoir for natural gas exploration, its genesis mechanism and the relationship between sedimentary environment and tectonic superimposed transformation, there are still many disputes, which restricts the guidance of oil and gas exploration.[Methods] Based on comprehensive test and analysis including thin-section identification, cathodoluminescence, carbon-oxygen isotope, X-ray diffraction order, geochemical rare earth and trace elements, and strontium isotope, combined with the regional tectonic evolution process, this study explores the genetic mechanism of dolomite.[Results] Cathodoluminescence overall exhibits a relatively weak dark brown coloration with distinct ring bands, and authigenic quartz and saddle-shaped dolomite as hydrothermal minerals are visible, characterized by features of multi-stage recrystallization and burial origin. Carbon and oxygen isotope characteristics indicate that the dolomite has a burial origin. The overall order of the dolomite shows a relatively low degree, and the higher the temperature, the lower the order, suggesting that the dolomite formed in an environment with relatively high temperature and rapid crystallization rate. The rare earth element partitioning pattern is characterized by positive Ce and positive Eu anomalies, indicating that the formation process of dolomite is the result of internal fluid adjustment and redistribution within the diagenetic system under relatively closed, high-temperature, and high-pressure conditions. The lower the Sr content and the higher the Fe and Mn element contents, overall showing the characteristics of multi-stage superimposed modification under deep burial conditions. The strontium isotope values of medium to coarse-grained dolomite are significantly close to the average value of crustal source strontium isotopes, which may have been affected by crustal source strontium carried by synchronous tectonic activities.[Conclusion] Research indicates that dolomite formation is primarily attributed to deep burial, while also undergoing superimposed tectonic fluid modification. The evolution of Ordovician Krimolli Formation dolomite is closely linked to the deep fault system. During the co-deposition period, this fault system controlled the development of high-energy terraces. In the subsequent tectonic activity phase, the deep fault system became a fluid migration channel, facilitating the superimposed modification of dolomite bodies.[Significance] Research results can provide a fundamental support for the efficient exploration of oil and gas resources.

Wu Chengjie^1,2，Zeng Huaien^1,2,3，Chen Jun⁴，FengYu⁵ , Li xi^2,3，WeiPengcheng^2,3,Yan Baorui^1,2

chengjie wu, HuaiEn CENG, jun chen, Yu FENG, xi li, pengcheng wei, baorui yan

doi: 10.12090/j.issn.1006-6616.2025077

[Abstract](387) [PDF 1363KB](322)

Abstract:
Accurate prediction of landslide displacement is a crucial component of landslide early warning systems. This paper proposes a landslide displacement prediction model based on Gaussian Process Regression (GPR) combined with diverse time-series feature engineering, achieving high-precision displacement prediction and uncertainty quantification. TAKING THE BAZIMEN LANDSLIDE AS AN EXAMPLE, During the feature engineering phase, displacement lag features, rolling mean of rainfall, rolling variance of reservoir water level, and displacement change rate are constructed. Additionally, temporal decomposition features including monthly and quarterly components are extracted. SUBSEQUENTLY, EMPLOY THREE-FOLD TIME SERIES CROSS-VALIDATION, ALONG WITH A GRID SEARCH SCHEME, TO OPTIMIZE HYPERPARAMETERS IN CONJUNCTION WITH THE TIME SERIES CROSS-VALIDATION STRATEGY, THEREBY MITIGATING THE RISK OF OVERFITTING IN THE SMALL-SAMPLE SCENARIO. The results demonstrate that after incorporating multi-source temporal features, the prediction coefficients of determination (R²) for monitoring points ZG110 and ZG111 at the Bazimen Landslide significantly increase to above 0.99. Metrics such as MAE, RMSE, and MAPE are substantially reduced, indicating a significant improvement in prediction accuracy. This study integrates probabilistic modeling with feature interpretability analysis. The proposed method achieves high-precision landslide displacement prediction in small-sample environments while simultaneously quantifying prediction uncertainty. It provides effective decision support for landslide risk early warning and engineering safety assessment.

Tectonic stress field characteristics in Wushi , Xinjiang and the stress impact of the Wushi M7.1 earthquake

ZeYao SONG, YongGe WAN, PeiYuan GU, MingYue ZHOU

doi: 10.12090/j.issn.1006-6616.2025085

[Abstract](386) [PDF 2767KB](345)

Abstract:
[Objective] The Wushi region in Xinjiang is located at the intersection of multiple tectonic units, making it a key area for stress concentration and release. Although previous studies have revealed some characteristics of the tectonic stress field in this region, there is still a lack of in-depth and systematic analysis regarding the potential impact of the 23 January 2024 Wushi M 7.1 earthquake on the regional stress field. Therefore, adopt more systematic focal mechanism data to conduct a detailed analysis of the regional tectonic stress field characteristics and to explore the influence of the Wushi M 7.1 earthquake on the regional stress field. The aim is to provide more comprehensive scientific references for understanding the regional seismogenic environment and predicting future seismic activity.[Methods] Using the damped stress tensor inversion method and incorporating data from multiple institutions, we analyzed the stress field in different subregions of the study area and compared the changes in the tectonic stress field before and after the earthquake.[Results] The results of the stress field inversion show that, except for the area near the Jiashi seismic group, the R value is greater than 0.5, and the azimuth of the maximum principal compressive stress in the Wushi region gradually rotates from approximately NNW in the south to near N—S in the north, the azimuth is from 168.75° to 183.45°, and plunge angle is from 6.85° to 19.58°, it is in a compressive stress state. The Jiashi seismic area cluster shows a strike-slip feature of NNE—SSW compression and NWW—SEE extension.The northern area of the Jiashi seismic shows a thrust stress state, while the southern area presents a strike-slip stress state. By comparing and analyzing the regional stress field changes before and after the Wushi earthquake, it is found that the optimal principal compressive stress direction before the earthquake was N—S direction, and deviated by 12.53° in azimuth after the earthquake, with a spatial rotation angle of 15.06°. This indicates that this earthquake had a relatively small impact on the stress field of this area, which meaning that the stress field did not undergo significant changes after the earthquake, and still remains in the compressive stress system. [Conclusion] The tectonic stress field in the Wushi region is subject to N—S compression from the collision of the Indian plate with the Eurasian plate on the western margin of the Tibetan Plateau to form a strong near-north-south horizontal compression, and the stress from the plate collision is transmitted to the northeast to the Tian Shan orogenic belt, which leads to the shortening of the crust and retrograde thrusting between the Tarim Basin and the Tian Shan. The Wushi M 7.1 earthquake had a relatively minor impact on the regional stress field. The stress system of the entire area is still controlled by deep tectonic activities. The overall stress field is consistent, but the seismic cluster in northern Jiashi is located at the junction of the northern margin of the Tarim Plate and the Tianshan Mountains, presenting a thrust stress mechanism. This area is the plate tectonic transition boundary between the Tarim Basin and the Tianshan orogenic belt.[Significance] By analyzing the characteristics of the tectonic stress field in the Wushi region of Xinjiang and the impact of the Wushi M 7.1 earthquake on the regional stress field, the characteristics of the stress field and the effect of earthquakes on the regional stress field. This contributes to a deeper understanding of the tectonic relationship between the Tianshan orogenic belt and the Tarim Basin. In addition, the northern part of the Jiashi seismic exhibits a thrust stress mechanism, which is inferred to represent a tectonic transition boundary between the Tarim Basin and the Tianshan orogenic belt. This finding holds significant implications for regional tectonic segmentation and seismic hazard assessment.

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Supervisor： China Geological Survey

Sponsor： Institute of Geomechanics, Chinese Academy of Geological Sciences; Geological Society of China (GSC)

Editor-in-Chief： DENG Jun

ISSN 1006-6616

CN 11-3672/P

Post Issue Number 82-124

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