Focal mechanism inversion and source depth locating of moderate-major earthquakes in the Sichuan region since 2010

Abstract

Focal mechanism solutions and accurate source depths of earthquakes are important for understanding seismicity and structure of seismic faults. This work collected the seismic wave data of earthquakes with magnitudes M≥5.0 and 5.0>M≥4.0,which occurred from January 1, 2010 to December 31, 2017, recorded by the national seismic network and the regional seismic network in Sichuan province. The focal mechanisms of these events were inverted applying the synthetic seismograms method. The results show that the earthquakes on the Longmenshan fault zone are of thrust focal mechanism. On the Xianshuihe fault zone, focal mechanism solutions are dominated by strike-slip. And in the southwest of the Sichuan-Yunnan block, normal faulting dominates the focal mechanism solutions. As the excitation energy of surface waves is sensitive to source depth, the surface wave amplitude spectrum is applied to determine the focal depth and compared with the results from China Earthquake Networks Center (CENC), the U.S. Geological Survey (USGS), and the International Seismological Centre (ISC). The sources of the moderate-major earthquakes in the Sichuan region are mainly distributed in the upper-middle crust above 20 km. In the Longmenshan region, seismic sources are concentrated in the depth range from 10 km to 20 km. On the Xianshuihe fault zone, focal depths are confined about 10km. In the southwest of Sichuan-Yunnan block, near the Litang and Jinshajiang faults, the depths of seismic sources are generally 5 km to 10 km.