基于远震P波、 强震波形和InSAR联合反演2025年西藏定日MS6.8地震破裂过程

doi:10.3969/j.issn.0253-4967.2025.03.20250033

摘要/Abstract

摘要： 2025年1月7日, 西藏日喀则市定日县发生 M_S6.8 地震, 震源深度10km, 震源机制反演结果表明本次地震发生在青藏高原申扎-定结正断层体系中走向SN、倾向W的登么错断裂, 矩心深度为6km, 破裂方向NNE。为了进一步揭示2025年西藏定日 M_S6.8 地震的破裂特征及发震构造, 文中分别基于单断层和双梯形断层模型, 综合远震P波、强震波形及InSAR同震形变数据, 对破裂过程进行了联合反演分析。结果显示, 定日地震为正断型事件, 伴随少量左旋走滑分量, 破裂时间约36s, 释放的地震矩为6.71×10¹⁹N·m, 对应矩震级为 M_W7.15。其破裂过程呈现出显著的不对称性, 主要破裂区域位于震中以北约10km深度范围内。该地震经历了3个主要阶段: 0-7s震中附近20km范围成核扩展(滑动量<1.3m); 8-24s破裂区域向N传播并达到峰值滑动(最大滑动量为4.3m), 在长所乡以北约20km范围内出现了长度>1m的地表破裂; 25-36s破裂传播至登么错断裂北端走向拐折处, 滑动速率迅速停止衰减。结合同震滑动和余震分布特征, 推测登么错断裂可能存在复杂的分支构造, 其中几何变化在一定程度上对破裂传播产生了阻挡作用。

关键词: 定日M_S6.8地震, 震源机制解, 破裂过程联合反演

Abstract:

At 09:05 Beijing time on January 7, 2025, a M_S6.8 earthquake struck Dingri County, Shigatse City, Xizang Autonomous Region, China, with a focal depth of 10km. The earthquake caused strong ground shaking, reaching a maximum intensity of Ⅸ on the China Seismic Intensity Scale, and resulted in 126 fatalities. This seismic event occurred along the Dengmoco Fault, which is part of the north-south-trending Shenzha-Dingjie normal fault system in the southern Qinghai-Xizang Plateau. The fault extends approximately 60km, dips westward, and has maintained a vertical slip rate of(0.28±0.04)mm/a over the past 1 000 years. Geological investigations indicate that the most recent paleo-earthquake on this fault occurred 4 800-4 968 a BP, with an estimated recurrence interval of(5 500±1 100)a in the Holocene. These characteristics demonstrate that the 2025 Dingri earthquake represents a typical event within the fault’s long-term seismic cycle.

To determine the source mechanism of this event, we performed a joint inversion of the moment tensor using teleseismic P waves and W-phase. By combining the relatively high-frequency P-waveforms with the low-frequency W-phase records, this approach enables a more robust determination of the focal mechanism while providing improved constraints on the centroid location, particularly the centroid depth. The results indicate a moment magnitude of 7.02, with a centroid time offset of 9.7s and a shallow centroid depth of 6km. The optimal centroid is located at(28.6°N, 87.5°E), about 24° east of north from the epicenter. The best-fitting focal mechanism solution yields two nodal planes: Nodal Plane 1 with a strike of 344°, dip of 48°, and rake of -105°; and Nodal Plane 2 with a strike of 185°, dip of 44°, and rake of -74°. Considering the west-dipping geometry of the Dengmoco Fault, Nodal Plane 2 is interpreted as the likely fault plane responsible for the rupture. Based on Nodal Plane 2, we further conducted a joint rupture process inversion using teleseismic P waves, strong-motion waveforms, and InSAR deformation data. The combination of seismic and geodetic observations provided complementary constraints, enhancing both the spatial and temporal resolution of the dynamic rupture process. The results indicate a predominantly normal faulting mechanism with a minor left-lateral component. The rupture propagated mainly northward, with limited southward extension. The rupture lasted approximately 36 seconds, with the main slip occurring between 8 seconds and 24 seconds and concentrated within depths of 0-10km, generating a significant surface rupture approximately 20km north of Changsuo Township. To further explore the fault geometry, we conducted a grid search using a dual-fault model to identify the optimal strike for the northern segment. The analysis identified 240° as the best-fit strike, which slightly improved the overall data fitting and exhibited better consistency with the surface topography. The resulting slip model retained the main rupture characteristics observed in the single-fault scenario. The rupture process can be divided into three stages: ① 0-7s initial nucleation near Cuoguo Township with a relatively minor slip(<1.3m); ② 8-24s primary rupture occurred approximately 20km north of Changsuo, with a peak slip of 4.3m; ③ 25-36s rapid slip attenuation after propagating beyond the northern fault bend.

Our study indicates that the complex fault structure plays a critical role in rupture dynamics. The relatively minor slip observed between Cuoguo Township and Changsuo Township, together with the sparse aftershock activity, suggests the existence of an unidentified east-dipping, NW-trending fault segment in this region. Additionally, the abrupt rupture termination near the northern segment of the Dengmoco Fault is likely influenced by an unrecognized NE-trending subsidiary fault. This study underscores the importance of rupture directivity in seismic hazard assessment and reveals the structural complexity of the Dengmoco Fault system. Overall, the results enhance our understanding of the seismogenic mechanism and contribute to more accurate earthquake hazard evaluations in the region.

Key words: Dingri M_S6.8 earthquake, focal mechanism solution, joint inversion of the rupture process

许月怡, 徐贝贝, 徐晨雨, 邵志刚, 胡朝忠. 基于远震P波、强震波形和InSAR联合反演2025年西藏定日M_S6.8地震破裂过程[J]. 地震地质, 2025, 47(3): 734-746.

XU Yue-yi, XU Bei-bei, XU Chen-yu, SHAO Zhi-gang, HU Chao-zhong. JOINT INVERSION OF THE 2025 DINGRI M_S6.8 EARTHQUAKE RUPTURE PROCESS BASED ON TELESEISMIC P WAVES, STRONG-MOTION AND INSAR DATA[J]. SEISMOLOGY AND GEOLOGY, 2025, 47(3): 734-746.

图/表 8

图1 定日地震的区域背景 a 地质构造背景, 灰色圈代表1970年以来震中附近3级以上地震震中 ① , 六角形为CENC确定的震中的位置, 菱形为不同机构反演的地震矩心位置, 蓝线和红线代表全新世断裂(徐心悦, 2019; 石峰等, 2025), 红色虚线表示本文推测的隐伏断层; b 震源时间函数; c 矩心深度搜索结果

Fig. 1 The regional background of the Dingri earthquake.

图2 反演使用的速度模型

Fig. 2 Velocity model used for inversion.

图3 联合反演中使用的形变点和台站分布 a InSAR同震变形场(王楠等, 2025); b 远震台分布; c 强震仪和烈度仪分布

Fig. 3 Distribution of deformation points and stations used in the joint inversion.

表1 SAR 数据信息

Table 1 Information of SAR data

卫星传感器	轨道方向	主影像日期	辅影像日期	空间基线/m	入射角/(°)	飞行方位角/(°)
LT-1	升轨	2024-12-06	2025-01-07	667.7	32	-13

图4 定日地震单断层联合反演破裂结果 a 滑动分布在地表上的投影, 灰色的圆圈代表截至2025年1月20日10点ML≥2的余震重定位目录(杨婷等, 2025); b 断层上的滑动量分布, 箭头指示滑移方向; c 震源时间函数; d 数据拟合残差随子断层持续时间和最大破裂速度的变化曲线

Fig. 4 The rupture results from single-fault joint inversion of the Dingri earthquake.

图5 定日地震双断层联合反演破裂结果 a 滑动分布在地表上的投影; b 断层上的滑动量分布; c 震源时间函数; d 最大值归一化残差随北段断层走向的变化曲线

Fig. 5 The rupture results from double-fault joint inversion of the Dingri earthquake.

图6 联合反演的数据拟合 a InSAR 数据拟合结果; b 远场P波拟合结果, 台站下方标注了方位角和震中距, 黑线、蓝线和红线分别代表观测波形、单断层拟合和双断层拟合波形; c 强震仪和烈度仪速度波形拟合结果, 黑色、蓝色和红色数字标注了观测波形、单断层拟合及双断层拟合波形的最大速率(0.02~0.4Hz滤波后)

Fig. 6 Data fitting in the joint inversion.

图7 定日地震断层面上的滑动速率随时间的变化快照

Fig. 7 Temporal snapshots of slip rate on the Dingri earthquake fault plane.

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