关键词: 定日M_S6.8地震, 登么错断裂, 同震地表破裂带, 申扎-定结裂谷, 遥感解译

Abstract:

On January 7, 2025, at 09:05, a M_S6.8 earthquake occurred in Dingri County, Shigatse City, Xizang, China, with a focal depth of 10km and an epicenter located at 87.45°E, 28.50°N, as per data from the China Earthquake Networks Center. Rapid identification of coseismic surface ruptures is crucial not only for determining the seismogenic structure but also for post-earthquake damage assessment and emergency response. Based on the objective geological conditions of the Dingri earthquake-affected area, preliminary interpretation of pre- and post-earthquake high-resolution remote sensing data to delineate the spatial distribution and geometric characteristics of coseismic surface rupture zones before field investigations can effectively guide emergency response teams in rapidly and accurately identifying coseismic surface ruptures and conducting subsequent field surveys. This methodology demonstrates high feasibility and necessity for optimizing field workflow efficiency and ensuring targeted structural analysis of seismogenic faults.

This study utilizes high-resolution imagery from the Gaofen -1 satellite to interpret pre- and post-earthquake images, rapidly obtaining the spatial distribution and geometric characteristics of the coseismic surface ruptures. The seismogenic fault is identified as the Dengmecuo Fault, located in the southwest segment of the Shenzha-Dingjie Rift. The coseismic surface rupture zone is primarily distributed near Gulong Village in the northern and central segments of the Dengmecuo Fault, with discontinuous extensions of approximately 15km, consistent with the location of the pre-existing fault. The coseismic surface rupture zone is tectonically partitioned into three distinct segments based on their geographic distribution: The Nixiacuo and Yangmudingcuo segments situated within the northern fault segment, and the Gurong segment developed along the eastern piedmont front of Gurong Village. These three segments exhibit marked differences in spatial scale and morphological characteristics between remote sensing observations and field investigations. The Nixiacuo segment exhibits linear and continuous coseismic surface ruptures, extending approximately 5km, with prominent linear traces visible in satellite imagery, facilitating clear identification. Field investigations reveal that this segment predominantly develops a series of large-scale tensional fractures and three categories of fault scarps with differential heights, with a maximum coseismic displacement of ~3m recorded. In contrast, both the Yangmudingcuo and Gurong segments exhibit smaller-scale coseismic surface ruptures localized along the eastern graben-bounding basin-range boundary. These secondary ruptures are characterized by minor extensional cracks with limited opening amounts(<1m vertical displacements)and fault scarps, manifesting as dark-gray linear features in remote sensing imagery that coincide with pre-existing rupture traces. Their partial obscuration in spectral signatures renders comprehensive visual interpretation impractical, necessitating field validation for complete delineation. Furthermore, this study identifies an ~10km-long associated surface deformation zone along the eastern Dengmecuo Lake shoreline, exhibiting a structural assemblage of extensional fissures proximal to the mountain front and compressional ridges adjacent to the lakeshore, with concomitant sand boil structures observed within the deformation zone. These extensional features present as dark-toned linear traces paralleling the main surface ruptures, displaying discontinuous arcuate configuration convex toward the mountain front within the mid-fan sector of alluvial fans. The compressional uplift zone west of the extensional belt appears as curvilinear bands with central whitish zones flanked by shadowed margins in imagery, demonstrating enhanced spatial continuity along distal fan margins.

The conclusions of this study exhibit high consistency with previous research based on submeter-level resolution remote sensing imagery, confirming the reliability of remote sensing interpretation. However, interpretations derived from 2m resolution imagery have inherent limitations, including difficulties in identifying small-scale surface ruptures and distinguishing surface deformations of diverse genetic origins. Based on existing research integrated with remote sensing image interpretation and field investigations, the identification capability of coseismic surface ruptures in 2m-resolution remote sensing imagery is fundamentally governed by the three-dimensional geometric parameters of the rupture zone—specifically, rupture zone width, along-strike continuity length, and fault scarp vertical displacement. From the case study of the Dingri earthquake, we hypothesize that GF-1 satellite imagery with 2m resolution is capable of resolving coseismic surface ruptures characterized by a minimum rupture width of 1m, along-strike continuity exceeding 10m, and vertical offset≥1m Furthermore, the composite deformation pattern observed along the eastern shore of Dengmecuo Lake, characterized by rear tensile fractures and frontal thrusting, is interpreted as shallow detachment sliding induced by seismic shaking, representing a secondary associated surface deformation zone rather than direct fault displacement. Therefore, the identification of coseismic surface ruptures necessitates integrating remote sensing interpretation with field investigations, requiring not only the analysis of their geometric configuration and vertical displacement but also a synthetic evaluation of genetic origin based on the geological environment to achieve comprehensive and accurate determination.

This study conducted a detailed interpretation of the coseismic surface rupture zone in the earthquake-affected area using GF-1 image data acquired within 24 hours post-earthquake, rapidly delineating the overall geometry and location of the coseismic surface rupture. This approach effectively supported subsequent field investigations and enhanced the efficiency of earthquake emergency response. Furthermore, rigorous field reconnaissance was carried out to validate the remote sensing interpretation results. The findings demonstrate a high consistency between the interpreted segments of the coseismic surface rupture and field observations, confirming the reliability of the remote sensing interpretation. This highlights the potential of domestic high-resolution satellite data for rapid coseismic surface rupture mapping and seismogenic structure identification, providing a feasible, rapid, and efficient methodology for future emergency response to major earthquakes.

Key words: Dingri M_S6.8 earthquake, Dengmecuo Fault, coseismic surface rupture zone, Shenzha-Dingjie rift, remote sensing interpretation