Numerical simulation of fault deformation and seismic activity in the southern Qinghai–Tibet Plateau

Abstract

The moderate-strong (M ≥ 5, since 1976; or M ≥ 6.5, overall) earthquakes of the north to south trending (NS-trending) faults and their vicinity in the southern Qinghai–Tibet Plateau exhibit prominent spatial concentration distribution characteristics. However, research on the southern Tibet faults is limited. Hence, this study used a two-dimensional viscoelastic finite element model to simulate crustal movement in southern Tibet based on 1991–2015 GPS velocity data. The current deformation field, tectonic stress field, fault slip, and stress accumulation rates distribution were obtained to analyze the relationship between fault activity and earthquake distribution. The results revealed that the simultaneous effected by of the NE-trending compression and uneven EW-trending tension on the study area. Crustal deformation exhibited simultaneous NS-trending compression and EW-trending stretching. The EW- and NWW-trending faults and the NS-trending faults differed in their mechanical properties and movement modes. The NS faults were primarily subjected to extensional stress with normal motion. The remarkable heterogeneity of the fault segments influenced the distribution of moderate-strong earthquakes and types of earthquake ruptures. The concentrated distribution of moderate-strong earthquakes on the NS-trending normal fault and its vicinity depended largely on the high slip rate, strong tensile stress, and geometric strike of the fault segment. This study aids in understanding the heterogeneity in normal fault activity in southern Tibet and is the basis for seismic hazard assessment.