Abstract:

According to the United States Geological Survey(USGS), a moment magnitude(M_W)7.1 earthquake struck Dingri County, Xigaze City, Xizang(28.65°N, 87.36°E)at 01:05:16 UTC on January 7, 2025(09:05:16 Beijing Time). The earthquake occurred at a focal depth of 10km and resulted in significant casualties: As of the afternoon of the same day, 126 deaths were confirmed, and approximately 61, 500 individuals were affected.

The Dingri earthquake occurred in the southern Qinghai-Xizang Plateau, a region characterized by intense tectonic activity due to the ongoing subduction of the Indian Plate beneath the Eurasian Plate. This area exhibits the typical seismic pattern of “frequent large earthquakes and persistent smaller events.” The epicenter is situated near the intersection of the Shenzha-Dingjie fault zone, south of the Yarlung Zangbo fault zone, and the South Xizang Detachment fault zone. The Dangra Yongco-Xuru Fault lies to the west, and the Shenzha-Dingjie Fault to the east, the latter exhibiting a north-south extensional structure that divides the South Xizang Detachment Fault into eastern and western segments. GPS observations indicate extension rates of 4~5mm/a for both the Dangra Yongco-Xuru and Yadong-Gulu fault zones, while the Shenzha-Dingjie fault exhibits a slower rate of 1~2mm/a. According to historical USGS records, over 700 earthquakes with magnitudes above M3 have occurred in this region since the 20th century, including 604 events in the M3-M5 range, 101 in the M5-M7 range, and two above M7. Most of these events are concentrated along the Himalayan Orogenic Belt and near the Shenzha-Dingjie fault zone. The occurrence of the Dingri earthquake underscores the region’s seismic complexity and highlights the importance of studying rupture dynamics for understanding earthquake mechanisms and assessing seismic hazards. There is a close correlation between the source rupture process and the earthquake expansion law. In-depth study of the source rupture process is helpful for a comprehensive understanding and analysis of the inducing factors of earthquake rupture, the complexity of the source environment, and its potential impact. Therefore, the inversion of the rupture process of this earthquake can provide a reference for earthquake disaster analysis, earthquake emergency rescue, and post-earthquake seismic trend analysis.

This study utilizes the rupture process inversion of the Dingri earthquake based on the source mechanism parameters(strike/dip/rake=187°/49°/-78°)provided by USGS and far-field waveform data from 51 stations within 30°~90° epicentral distances, sourced from the IRIS database. The analysis employs the AK135f global 1-D velocity model and the Iterative Deconvolution and Stacking(IDS)method proposed by Zhang (2014). The IDS method integrates advantages of both network-based and back-projection approaches and enables automated rupture process inversion without preset rupture time constraints. It has been successfully applied to events such as the 2015 Nepal and 2017 Jiuzhaigou earthquakes. The inversion results indicate an asymmetric bilateral rupture pattern with shallow rupture propagation. The maximum slip reached approximately 2.3 meters, with the rupture occurring primarily within a 0~9km depth range. The total seismic moment was 5.5×10¹⁹ N·m, corresponding to an M_W of 7.1. The rupture lasted 29 seconds, peaking in moment release at 16 seconds, with most rupture ceasing by 28 seconds.

The above results of this study align well with those of other studies, showing a maximum variation in magnitude of 0.1(range: M_W7.0-7.2)and a slip difference of less than 1 meter(range: 1.5~3.2m). Despite this agreement, however, debate remains regarding whether the rupture was unilateral or bilateral. Contributing factors include variations in input source parameters, rupture initiation locations, station distribution, and inversion uncertainties. However, the distribution of aftershocks on both sides of the rupture supports the bilateral rupture interpretation. Based on these findings, this earthquake is interpreted as a normal-faulting event with an asymmetric bilateral rupture along the Shenzha-Dingjie fault zone. The concentration of slip near the surface suggests that upper crustal structures are more fragile and play a key role in seismic energy release, potentially explaining the severity of the disaster. These results emphasize the need for closer monitoring of near-surface fault slip potential in this region.

Key words: The 2025 Dingri earthquake, waveform inversion, rupture process, slip distribution

摘要： 2025年1月7日西藏定日发生 M_W7.1 地震, 该地震造成重大人员伤亡, 对该地震进行破裂过程反演可为地震灾害分析、 地震应急救援、 震后地震趋势分析等提供参考。文中基于USGS发布的震源机制参数(走向、 倾向、 滑动角分别为187°、 49°、 -78°)及IRIS提供的远场地震波数据, 利用迭代反褶积和叠加(IDS)方法反演得到定日地震的破裂过程。结果显示, 震源破裂呈现非对称双侧破裂特征, 与余震精定位一致性较好, 其破裂区域位于地表附近, 最大滑动量约2.3m, 破裂主要影响深度范围为0~9km; 释放总地震矩为5.5×10¹⁹N·m, 震级为 M_W7.1, 地震持续29s, 地震矩释放率于16s时达到顶峰, 28s后大部分区域停止破裂。研究表明, 本次地震为发生在申扎-定结断裂带上的正断型地震, 滑动分布浅层集中趋势反映了地表结构较深层更为脆弱, 表明该区域浅部断层活动可能主导强震能量释放, 这可能是此次地震破坏性较强、 震害严重的原因之一。

关键词: 定日地震, 波形反演, 破裂过程, 滑动分布