关键词: 地震现场调查, 西藏定日地震, 地震灾害, 烈度, 震害特征

Abstract:

This study presents a field investigation and damage analysis of the Dingri M6.8 earthquake in Xizang, which occurred at 09:05 on January 7, 2025. Combined with emergency products derived from seismic monitoring data, this paper provides a comprehensive overview of casualties, focal mechanism, estimated intensity, and surface rupture characteristics. Differences between rapid intensity assessment results and field-surveyed intensity results are compared, and the damage characteristics of different building types within each intensity zone are summarized. The results indicate that the earthquake occurred in a region with strong fault activity and produced severe damage, with the maximum intensity reaching Ⅸ in the epicentral area. The surface rupture extended for approximately 26km, with a maximum vertical displacement of about 3m. The rupture zone passed through Changsuo township, Dingri county, causing severe damage to buildings near the fault and resulting in substantial casualties. Although Changsuo township is located approximately 16km from the epicenter, its death toll and mortality rate were higher than those of Cuoguo township, which is only about 3km from the epicenter, indicating the complexity of the rupture process of major earthquakes and the possible discrepancy between the instrumental epicenter and the area of strongest macroseismic effects. The earthquake occurred within the Shenzha-Dingjie tectonic rift zone at a shallow focal depth of approximately 10km. The shallow source depth, together with the relatively soft soil conditions of the plateau river floodplain, amplified the destructive effects of strong ground shaking. In addition, the seismic fortification intensity of buildings in the severely affected area was lower than the actual seismic intensity. More than 98% of the houses in the earthquake-stricken area were earth-wood structures. Traditional Tibetan dwellings in the epicentral area were mostly unconstrained stone-wood or earth-wood structures, which were highly vulnerable to collapse and disintegration under strong shaking. The overall collapse rate in the intensity Ⅸ zone exceeded 60%. The limited indoor survival space after collapse, combined with heavy roofs and walls, was the primary cause of the high casualty rate. The earthquake occurred in the early morning, when most residents were asleep, leaving little time for emergency response or evacuation. Fatalities were therefore concentrated among sleeping residents, with elderly people and children accounting for a relatively high proportion. Rescue operations were further constrained by the high-altitude plateau environment and severe winter conditions, with temperatures reaching approximately -18℃, which accelerated energy loss among buried victims and increased mortality among trapped and injured individuals. Based on these damage characteristics, this study proposes countermeasures including strengthening the management of rural residential construction, advancing investigations of the seismotectonic environment in the disaster area, avoiding known active faults in post-earthquake reconstruction site selection, and improving the accuracy of seismic intensity zoning maps.

Key words: earthquake field investigation, Xizang Dingri earthquake, earthquake disaster, earthquake intensity, seismic damage characteristics