A Comprehensive Seismological Investigation of the Anninghe-Zemuhe Fault Zone With a Dense Array

Date: 4/25/2019

Time: 10:45 AM

Room: Pike

The Anninghe-Zemuhe fault zone is located at the junction of the Chuandian block, the Bayanhar block and the Southern China block, and is an important eastern boundary of the Chuandian block. The fault is approximately 240 km long with prominent left-lateral slip. Previous geological and seismicity studies conjecture that the fault has a potential for generating a M7.0 earthquake in the near future. We have deployed 30 temporary broadband seismic stations along Anninghe-Zemuhe fault zone since January of 2013. The inter-station distance varies from 8 to 20 km. Each station is equipped with CMG-3T (120s) seismometers and Ref Tek 130 digitizer. The array records more than 13,600 local earthquakes. The magnitude ranges from M_L-0.9~M_L5.0. The micro seismicity delineates several faults which are not identified before. The seismicity and focal mechanism reveal clear segmentation of the fault. Most of the earthquakes occurred in the north part of the Anninghe fault. We find obvious change in focal depth in Shimian city. To the east of the fault, the earthquakes are concentrated in 17~35 km. While to the west of the fault, the earthquakes are in 0~17 km. We conducted travel time tomography with local earthquakes and ambient noise. Compared with previous studies, the lateral resolution has been improved greatly. The resolution is about 20 km in the central Anninghe-Zemuhe fault zone, and 20~40 km in other regions. The velocity structure is basically consistent with the surface geological structure. Fault zone head wave and body wave travel time tomography show clear velocity contrast along the both sides of the Anninghe fault. The P-wave velocity in the eastern side is faster than that in the western side. We propose that the focal depth changes perpendicular to the Anninghe fault is mainly controlled by velocity structure.

Presenting Author: Lihua Fang

Authors