Shallow and deep structural characteristics of the west branch of the Nantinghe fault: evidence from deep seismic reflection profiling

Sourthwestern Yunnan Province hosts a NE-trending fault zone consisting of many faults, on which several major earthquakes have taken place successively in past decades. This work focused on the west branch of Nantinghe fault zone. Using deep seismic reflection profiling, we have imaged fine crustal structures and tectonics beneath the fault and either side of it. The results show that the crust of this area is 31. 25 similar to 35. 6 km thick, comprisings two layers. On either side of the west branch of Nantinghe fault, reflection features diffent much, dominated by arc-like and tilting reflective wave sets, respectively. Along the profile,the Moho interface can be identified by reflective strips made up of 2 or 3 reflection events. The west branch of the fault zone is composed of 5 faults that exhibit a flower structure indicative of a stress state of strike-slip and compression. Beneath the fault zone, there is a deep fault cutting low crust and the Moho and extending downward to upper mantle. Such a coexistence structural pattern of shallow and deep faults is one of the factors to control seismicity in the Nantinghe area.