Focal mechanism and stress field of the Wushi <italic>M</italic>_S7.1 Earthquake sequence on January 23, 2024

Based on observational data recorded by the Xinjiang regional digital seismic network, the CAP method was used to calculate the focal mechanism and focal depth of the Wushi MS 7.1 mainshock on January 23, 2024, as well as some MS≥3.5 aftershocks. Furthermore, by combining these results with the focal mechanisms of historical earthquakes, we analyzed the variation characteristics of the principal compressive stress (S1) near the Maidang fault zone in the southwest Tianshan region and in the Wushi aftershock area. We also analyzed the temporal variation of the focal mechanism consistency parameter near the Maidang fault zone before the Wushi MS 7.1 earthquake. The results show that, for the Wushi MS 7.1 earthquake, the focal depth is 13 km, nodal plane I had a strike of 236°/dip of 54°/slip angle of 52°, while nodal plane II had a strike of 109°/dip of 50°/slip angle of 130°. The P-axis azimuth was 352°/plunge 2°, nearly horizontal, and the T-axis azimuth was 86°/plunge 60°. This results indicate that the earthquake was primarily thrust-slip, accompanied by a minor left-lateral strike-slip component. Considering the structural characteristics of the affected area and the spatial distribution of aftershocks, the seismogenic fault was determined to be the NE-trending Maidan Fault. Prior to the earthquake, compressional stress in the NNW direction controlled the tectonic environment of the region. Earthquake location results revealed an earthquake gap near the Wushi MS 7.1 mainshock, with the aftershock sequence clearly divided into NE and SW segments. To better understand tectonic and stress differences between the two sides of the mainshock, we calculated the stress fields in these regions. The stress direction of the NE segment was 172.8°, while that of the SW segment was 165.4°, a difference of 7.4°. Although this value is slightly larger than the error range, it does not represent a significant discrepancy. We infer that the earthquake gap near the MS 7.1 mainshock likely resulted from a relatively complete rupture of the mainshock, which released sufficient energy in this region. Furthermore, prior to the 2024 Wushi MS 7.1 earthquake, both the stress tensor variance and the misfit angle (β value), parameters reflecting focal mechanism consistency, showed a decreasing trend near the Maidang fault zone in the southwest Tianshan Mountains. This indicates increasing stress-field consistency before the earthquake. After the mainshock, however, the variance and β values gradually increased, suggesting decreasing consistency and a tendency toward disorder in the focal mechanisms of subsequent small- and moderate-magnitude earthquakes.