Focal Mechanism and Stress Field of the Wushi 7.1 Earthquake Sequence on January 23, 2024

Abstract

Based on observational data recorded by the digital seismic network in Xinjiang, the Cut and Paste (CAP) method was used to calculate the focal mechanism solutions and focal depths of the main shock of the Wushi M_S 7.1 earthquake on January 23, 2024, and some aftershocks with M_S > 3.6. By combining the focal mechanisms of historical earthquakes, the principal compressive stress (S1) in the Keping block and the Wushi aftershock area were analyzed. The changes in the focal mechanism consistency parameters of the Keping block before the Wushi M_S7.1 earthquake over time were examined. The focal mechanism solution of the Wushi M_S 7.1 earthquake for Nodal Plane I was: strike 251°/dip 50°/rake 68°; for Nodal Plane II: strike 103°/dip 45°/rake 114°, with a p-axis orientation of 343° and a focal depth of 18 km. Therefore, the M_S 7.1 earthquake event was predominantly a thrust faulting with a minor left-lateral strike-slip component. Combined with the tectonic characteristics and the spatial distribution of aftershocks in the earthquake area, the seismogenic fault was determined to be the Maidan fault trending NE, with the NNW nearly horizontal compressive stress controlling the tectonic environment in the area. The Wushi M_S7.1 aftershock sequence was divided into NE and SW segments. The focal mechanisms of the aftershocks in the NE segment were mostly similar to the main shock, indicating that their ruptures were largely controlled by the main shock. However, some earthquakes in the SW segment showed significant differences in rupture direction and type compared to the main shock. The stress direction in the NE segment was 176°. Meanwhile, in the SW segment of the aftershock area, it was 158°, differing by 18°, indicating a slight change in the stress orientation from SW to NE. Before the 2020 Jiashi M_S 6.4 earthquake and the 2024 Wushi M_S 7.1 earthquake, the misfit values of the focal mechanism consistency parameters of the Keping block showed low values, reflecting an increase in regional stress before the earthquakes.