关键词: 定日地震, 地表破裂, 最大垂直位移, 地表变形样式

Abstract:

On January 7, 2025, at 9:05 AM, a M_S6.8 earthquake occurred in Dingri County, Shigatse City, Xizang Autonomous Region. The epicenter was located at 87.45°E and 28.50°N, with a focal depth of 10 kilometers, as determined by the China Earthquake Networks Center. Regarding the maximum vertical displacement of this earthquake, there are differing opinions due to variations in the reference markers used during field measurements of coseismic displacement or deformation amplitude, as well as divergent understandings of the deformation style of earthquake scarps and pre-existing scarps. Additionally, factors such as the complex structure of the surface rupture zone and the short duration of field investigations contribute to the current discrepancies in understanding the maximum co-seismic displacement. Different scholars have varying perspectives on this matter. To determine the maximum co-seismic displacement and provide data for subsequent research, this study utilized GF1 satellite imagery and drone aerial surveying technology to measure the maximum co-seismic displacement following the earthquake.

The seismogenic fault of the Dingri earthquake is the Dengmecuo Fault. The surface rupture caused by this earthquake is mainly concentrated near Nixiacuo, at the northern end of the Dengmecuo Fault. The surface rupture trace in the Nixiacuo section is evident, striking northeast and arranged in a linear pattern. It develops along the existing steep scar in front of the mountain, cutting through a series of landforms, including alluvial fans and moraines, and aligns well with the original steep scar. This section of surface rupture is large in scale, developing a series of extensional fractures and fault scarps. The surface rupture phenomenon is most pronounced at a location 800 meters north of Nixiacuo, where the largest co-seismic vertical displacement also occurs. At the location of the maximum co-seismic vertical displacement, the main rupture diverges into several secondary ruptures, which later converge back onto the main rupture. Simultaneously, several extensional fractures develop, and a clear vertical displacement is observed between the hanging wall and the footwall, accompanied by rock collapse. This study employed field observations and UAV aerial survey technology to determine the maximum coseismic surface displacement resulting from the Tingri earthquake. Since the surface rupture generated not only vertical displacement but also ground fissures, leading to some horizontal displacement, the displacement could not be measured directly. To address this, we identified two points on the hanging wall and footwall of the fault, measured the distance l between them, and determined the inclination angle θ of l relative to the ground. The vertical displacement was then calculated using the trigonometric relationship l ×sinθ. Four sets of measurements were taken, yielding a result of(2.47±0.1)m. UAV aerial survey technology was used to capture orthophotos of the location with the maximum coseismic vertical displacement. Three profiles were measured, and the largest recorded coseismic vertical displacement was 0.2m.

In this study, we collected empirical formulas derived from the maximum moment magnitude of the Dingri earthquake inverted by other scholars. The calculated maximum co-seismic surface displacement ranged from 2.37m to 2.97m, which is consistent with the(2.47±0.1)m observed in the field and the(2.6±0.2)m obtained using drone aerial survey technology. The moment magnitude of the Yutian earthquake is equal to that of the Dingri earthquake, but its maximum co-seismic surface displacement is smaller than that of the Dingri earthquake. Firstly, the Yutian earthquake exhibited both left-lateral strike-slip and normal fault characteristics, whereas the Dingri earthquake was mainly characterized by normal faulting. Secondly, the Yutian earthquake produced relatively continuous surface ruptures, whereas the Dingri earthquake produced highly discontinuous surface ruptures with significant displacement differences between segments.

Key words: Dingri earthquake, surface rupture, maximum vertical displacement, surface deformation style