A Study on the Possibility of the Reactivation of the Fault System in the Western Part of the South China Sea as a Source of Geological Hazards

Tran Tuan Dunga, b, *, R. G. Kulinichc, **, Nguyen Quang Minha, d, ***, Nguyen Van Sange, ****, Tran Tuan Duong a , Nguyen Trung Thanha , Nguyen Ba Daia , Tran Trong Lapa , Nguyen Kim Dunga , Dang Xuan Tungf, *****, Dao Dinh Chamg, ******, and Nguyen Thai Song

Received April 24, 2021; revised June 10, 2021; accepted July 21, 2021

Abstract

This article summarizes the results of research on the possible reactivation of the fault system in the Earth’s crust of the South China Sea with likely dangerous consequences for the coastal area of Vietnam. The research was carried out over several years with the publication of interim results. The solution to this problem required the determination of the regional stress field in the Earth’s crust. Analysis of the focal mechanisms of local earthquakes, as well as the structural characteristics of faults obtained by gravity and seismic data was used. The possibility of renewal of fault activity was determined by the inversed-stress method in the calculated regional stress field. The parameters of the present-day stress field were used to estimate the required slip force along the pre-existing faults. The possibility of horizontal and vertical structural (block) displacements in the Earth’s crust of the study area was calculated to assess the probability of reactivation of the entire system of faults. Based on a comprehensive analysis of the data, a forecast of the probability of reactivation of the fault system in the South China Sea has been made. This could be the cause of earthquakes, underwater landslides, and other dangerous natural processes in the coastal area of Vietnam.

Keywords: the South China Sea, fault system, earthquake’s focal mechanisms, regional stress field, gravity and seismic data, forecast of reactivation possibility of faults.