Study on the Stress Characteristics of the Aftershock Sequence of the 2025 Dingri, Tibet MS6.8 Earthquake

According to the China Earthquake Networks Center (CENC), an M_S6.8 earthquake occurred in Dingri County, Tibet Autonomous Region, China, on January 7, 2025, with a focal depth of 10 km. The epicenter was located in the southern part of the Tibetan Plateau. Due to the northward push of the Indian Plate, a series of north-south trending rifts have formed within the block containing the epicenter. The seismogenic fault is identified as the Dengmocuo Fault in the southern segment of the Shenzha-Dinggye Rift. Within one week after the mainshock, 55 earthquakes of M_S≥3.0 were recorded, including one aftershock of M_S≥5.0—an M_S 5.0 event on January 13th. Focal mechanism solutions from different institutions consistently indicate that the mainshock was an extensional rupture event with a nearly north-south striking plane, essentially consistent with the trend of the Shenzha-Dinggye Rift. Based on the CENC catalog, earthquakes of M_L≥3.0 within the aftershock zone are overall distributed along a north-south orientation. The epicentral distribution map shows that, bounded by latitudes 28.8°N and 28.6°N, the aftershock zone can be divided into three main areas: northern, central, and southern. The mainshock is located in the southern area. M_L≥3.0 aftershocks are primarily distributed in the northern and southern areas, with fewer and more scattered events in the central area.

We collected waveform data for earthquakes of M≥3.0 within the aftershock zone from January 7 to 14. After quality screening, we determined the focal mechanism solutions for moderate and small earthquakes based on P-wave first motions, obtaining solutions for a total of 30 events. The results show that the focal mechanisms in the northern and central areas are predominantly strike-slip, although the number of solutions from the central area is limited. The focal mechanisms in the southern area are relatively complex, mainly characterized by extension with a subordinate strike-slip component. Subsequently, we inverted the regional stress field. Given that the aftershocks are basically aligned north-south with a narrow east-west distribution, we calculated the stress field from south to north at intervals of 0.2 degrees using a radius of 20 km. The calculation results show that the orientation of the maximum principal compressive stress (σ₁) within the aftershock zone is essentially north-south, indicating that the overall rupture is dominated by east-west extension. Furthermore, the R-values from north to south are 0.8, 0.5, 0.1, and 0.2, respectively. This reveals a gradational stress pattern across the entire aftershock zone: "strong compression in the north → weak planar stress in the central area → weak compression in the south," with no abrupt changes. This suggests that the post-mainshock stress adjustment is continuous and controlled by the regional tectonic setting, with no significant stress discontinuity. A transition in the stress state from compression in the north to extension in the south is observed.