Seismogenic structure analysis of earthquake surface rupture zone in Maisu Fault

In view of the obvious surface rupture phenomenon found in the satellite image interpretation of the northern section of the Jinshajiang fault zone. In this paper, 578 seismic events in the area of 31.55°−31.85°N and 98.31°−98.98°E were obtained by the double-difference locating method based on the continuous seismic waveform data from December 2020 to July 2022 obtained by the dense array observation set up around the seismic surface rupture zone; the HSAH method based on initial motion of P wave was used to invert focal mechanism solutions, and 37 groups of focal mechanism solutions were obtained; the stress environment of the study area is analyzed based on the inversion method of stress field in damped area of focal mechanism solution. The relocation results show that there is a WNW-ESE dense strip about 40 km long along the seismic surface rupture zone in the study area, and the focal depth is 3−10 km, showing a steep dip to the north, and there is also a NNW-SSE trending seismic dense strip with a length of about 30 km and the focal depth dense distribution range is 3−11 km, showing a steep dip to the west; the results of focal mechanism analysis show that strike-slip type are dominant in the study area, accounting for 51.4% of the results, and there are also a few reverse fault types and normal fault types. The dominant azimuth of the focal mechanism solution P axis is near NW-SE trending, which is similar to the direction of the maximum principal compressive stress axis σ₁ 323°; the P and T axes, as well as the maximum compressive stress σ₁ and minimum compressive stress σ₃ axes have small dip angles in general, which indicates that the horizontal compressive stress state in the study area is nearly NW-SE trending; the type of stress structure is strike slip, which is the same with the location and focal mechanism solution; R＝0.57, indicating that the maximum compressive stress axis σ₁, the intermediate compressive stress axis σ₂ and the minimum compressive stress axis σ₃ are basically arranged in an isometric manner, in which σ₁ and σ₃ are clear. The WNW-ESE trending seismic dense strip has dextral strike-slip with both normal and reverse fault components, while the NNW-SSE trending seismic dense strip has sinistral strike-slip characteristics with conjugate fault characteristics. It is concluded that an earthquake of magnitude 7 or above has occurred in the study area; The stress state of the nearly NW-SE trending horizontal extrusion is related to the strong sinistral strike slip of the NW-SE trending Ganzi-Yushu-Xianshuihe fault.