Activity characteristics of moderate and small earthquakes and fine crustal feature beneath Weiyuan, Sichuan and adjacent areas

In this work, we collected the seismic travel-time data from a local dense array in the Rongxian-Weiyuan area since 2019 and the seismic networks. Double-difference seismic tomography method was used to invert the high-resolution three-dimensional velocity structure and hypocentral locations. The results show that most of moderate and small earthquakes occurred in NS trending clusters, which are not associated with known faults. Their focal depths generally range 2 similar to 5 km. These events are associated with velocity anomalies, mostly occurred at the high V-s anomalies above depth 5 km, while in the high-to-low anomaly transition zones of V-P and V-s in the depth range of 7 similar to 10 km. Synthesis of the relocation and velocity profile permit to speculate that the thickness of sedimentary cap is about 4 similar to 6 km, and some moderate earthquakes took place in crystalline basement. In the deep subsurface, higher P wave velocity anomalies are present in the seismic area north of the Huangjuepo fault compared with the Rongxian seismic area. In a similar stress state, the seismic area north of the Huangjuepo fault with larger strength is more difficult to rupture, which may be the reason for later occurrence of earthquakes in this region.