Seismicity in Zemuhe fault zone based on dense seismic array

Based on the continuous waveforms of twenty portable broadband seismic stations deployed in the Zemuhe fault and six local stations in the surrounding areas of the fault zone in the period of 2019−2021, we performed automatic earthquake detection with an integrated event detection system called PAL, and then obtained the absolute earthquake catalogue in the study area by using traditional absolute positioning technology, finally relocated 1 075 detected seismic events by the double-difference positioning method. The results show that: ① The seismic activity in the study area is unevenly distributed, and most of the earthquakes are distributed in strips along the deep-large fault zones, showing the distribution pattern of the fault on the surface; ② The focal depth of the earthquakes in the study area ranges 5−15 km, which indicates that the earthquake occurred in the middle to upper crust; ③ The distribution characteristics of earthquakes at the depth of each section show the structural characteristics of faults in the deep. It can be seen from the spatial distribution of the epicenters after relocation that there is a small earthquake dense zone with dip of 60° in the middle section of the Zemuhe fault zone. The analysis shows that the small earthquakes have been frequent since the study period, the local stress in this area is high, and the tectonic activity is strong.