Abstract:

At 09:05 on January 7, 2025, a magnitude M_S6.8 earthquake struck Dingri County, Shigatse City, in the Xizang Autonomous Region of China. The earthquake had a focal depth of 10km and is the largest event in the region in recent years, resulting in severe damage and a wide area of impact. The disaster caused over 120 fatalities, damaged approximately 27,000 dwellings, and led to the collapse of 3600 structures. This study presents a comprehensive analysis incorporating seismogenic structures, historical seismicity, earthquake sequence evolution, and intensity mapping.

The epicenter is located within the Lhasa Block of the Tibetan Plateau, in the high-altitude valleys and basins north of the Himalayan mountain range, where elevations exceed 4,000m within a 10km radius. The tectonically active Lhasa Block includes multiple fault systems. The earthquake likely originated on the Dengmecuo fault, a segment of the Shenza-Dinggye Rift fault zone, which trends approximately north-south. Since 1900, the region within 300km of the epicenter has experienced 15 earthquakes of magnitude M_S6.0-6.9, and notable larger events include the M_S8.1 Nepal earthquake of April 25, 2015, and its aftershocks.

According to the China Earthquake Networks Center, the event had a moment magnitude of M_W7.1 and a centroid depth of 15km. The focal mechanism indicates normal faulting. The radiated seismic energy was approximately 10¹⁵ J. The moment and energy magnitudes both exceed the surface-wave magnitude, suggesting an efficient release of seismic moment and energy during rupture. The aftershock sequence extends approximately 75km in a north-south direction, aligned with the inferred fault strike. Aftershocks were concentrated near the mainshock and its northern extent, separated by a relatively quiet central segment.

Intensity analysis indicates a maximum intensity of Ⅸon both the United States Geological Survey(USGS)simulated intensity map and the measured intensity map from the China Earthquake Administration. The meizoseismal area follows a north-south distribution consistent with the fault trend. The Ⅵ-degree isoseismal zone in the USGS map extends nearly 200km in a north-south orientation, while the measured map shows isoseismal lines trending NNE, with a long axis of about 191km and a short axis of 152km. The orientations of the isoseismal lines and the meizoseismal area in both maps are broadly consistent, though discrepancies exist in areal extent and coverage. Notably, the simulated intensity in the northern part of the aftershock zone is higher than that of observed. This discrepancy likely arises from the fact that the area is sparsely populated, with no significant structural damage or reported casualties.

Key words: Dingri M_S6.8 earthquake, earthquake sequence, aftershock sequence distribution, earthquake Intensity

摘要： 2025年1月7日9时5分西藏日喀则市定日县发生6.8级地震, 该地震位于申扎-定结断裂南段, 是该地区近年来震级最大的一次地震, 造成了较为严重的地震灾害。文中结合发震构造和历史、 地震序列演化特征、 地震烈度图等资料开展综合研究。结果表明, 定日地震发生在青藏高原内部的拉萨地块, 震中附近历史地震活跃; 此次地震余震呈SN向分布, 与推测的发震断裂走向较为一致; 美国地质调查局给出的模拟烈度和中国地震局发布的实测烈度极震区的长轴方向、 范围、 最大烈度基本一致, 余震区北部实测烈度相较于模拟结果偏小, 综合分析认为这主要是由于该区域位处无人区, 无建筑物损毁和人员伤亡。

关键词: 定日6.8级地震, 地震序列, 余震分布, 地震烈度