The regional tectonic stress field reflects the distribution of crustal stress and plays an important role in revealing geodynamic processes and investigating fault interactions. On January 23, 2024, the Wushi M_S7.1 earthquake and multiple felt earthquakes occurred on the Maidan fault, which connects the Kalpin nappe structure and the South Tianshan orogenic belt. Therefore, it is of great significance to clarify the source rupture mechanism of earthquakes in the Kalpin region and explore the present-day characteristics of its tectonic stress field.

This study first collected the results of GCMT （global centroid moment tensor） focal mechanism solutions for moderate-strong earthquakes in the Kalpin area from 1991 to 2005; Secondly, using the broadband waveform data from Xinjiang seismic network from 2004 to 2024, the CAP （cut and paste） method was used to supplement the calculation of the focal mechanism solutions for earthquakes with M_S≥3.5 in the study area; Then, the regional stress tensor damping （MSATSI） method was used to invert the spatial distribution of stress in the Kalpin area, and finally the zoning characteristics of its stress field were explored.

In the process of calculating the focal mechanism solution, this study selected four earthquakes as examples and compared the focal mechanism solution results provided by other institutions, further verifying the reliability of the CAP method inversion used in this study. The results indicate that the focal mechanism solutions for earthquakes in the Kalpin area is mainly of the reverse fault type. The results indicate that the focal mechanism solutions of earthquake events in the Kalpin area are mainly of the reverse fault type, with reverse fault earthquakes accounting for 66.67% of the total number; Strike slip earthquakes account for 16.43% of the total number, while reverse strike slip earthquakes account for 13.62% of the total number from the P−axis and T−axis spatial distribution and parameter normalization statistics of the focal mechanism solution results, it can be seen that the dominant orientation of the principal compressive stress axis （P−axis） is concentrated in the NNW direction, and the dip angle is concentrated between 0° and 30°; The dominant orientation of the tensile stress axis （T−axis） is concentrated in the EW direction, and the dip angle is mainly distributed in the range greater than 60°. The focal depth of earthquakes in the Kalpin area is concentrated in the range of 5—30 km, with the depth of earthquakes in the western section gradually increasing from south to north. The seismic events in the eastern section are concentrated in the Wushi M_S7.1 earthquake sequence on January 23, 2024, with the focal depth mainly concentrated between 5—15 km; The largest earthquake was the Wushi M_S7.1, the strike, slip and rake are 246°, 68°, and 80° for nodal planeⅠ, and those are 91°, 24°, 113° for nodal planeⅡ, respectively. The moment magnitude of the mainshock is M_W7.1, and the centroid depth of the mainshock is at 27.0 km form CAP inversion.

In the process of stress field inversion, this study divided the research area into four regions based on the seismic distribution characteristics. Overall, the regional tectonic stress field is dominated by compressive stress, and the dominant direction of the principal compressive stress axis is the NNW direction. There is a certain deviation from the NS direction of the GPS （global positioning system） horizontal velocity field in the area from 1991 to 2016, which is caused by the stress difference between the deep part and the surface of the entire Kalpin nappe structure. The stress form factor R value ranges from 0.58 to 0.63. Stress inversion based on 213 focal mechanism solutions shows that the principal compressive stress axis σ1 in all four subregions is consistently oriented NNW; The tilt angle range of σ1 is 0.13°—6.78°, the tilt angle range of σ 2 is 9.70°—24.30°, and the tilt angle range of σ3 is 82.26°—88.85° To verify the reliability of stress field inversion in this study, the grid search method was used to solve the stress field, and the optimal axial direction angle was obtained to be 175.22° and the tilt angle to be 1.84°; The strike angle of the intermediate shaft is 266.00° and the tilt angle is 23.00°; The axial direction angle is 80.89°, the dip angle is 66.92°, and the range of axial direction angle at 90% confidence is 175.19°—176.22°, and the dip angle range is 1.83°—2.34°; The range of the strike angle of the intermediate shaft is 265.50° —267.00°, and the range of the tilt angle is 22.50°—24.00°; The range of axial strike angle is 80.39°—81.89°, and the range of tilt angle is 66.42°—67.92°.

From the perspective of regional tectonic stress field analysis, the Kalpin nappe structure can be treated as a unified seismic zone in future earthquake trend forecasting research and applications. The development of this study can provide reference for the subsequent seismic hazard assessment and geodynamic research in the study area.