Sectional fault-inclination-change based numerical simulation of tectonic stress evolution on the seismogenic fault of Madoi earthquake

2021 Madoi earthquake (M-s = 7. 4), a left-lateral strike-slip earthquake happened in Bayan Har block which lies on the Tibetan plateau, caused obvious surface ruptures with length of 150 km along the seismogenic Jiangcuo fault and of branching pattern at both ends of rupture zones. In this study, based on the segmental features of fault inclinations and strikes obtained from the three-dimensional (3D) spatial distribution of epicenters of mainshock and its aftershocks, a 3D finite element model of seismogenic fault was constructed, and the evolution of tectonic stress on the seismogenic fault was investigated numerically by considering the GNSS velocity field, viscoelastic constitutive relation, and the Coulomb criterion. The results illustrate that the accumulative velocities of Coulomb stress and the effective tectonic stress at three regions, including the ends of west (<10 km) and east sections of the seismogenic fault, and the region corresponding to the hypocenter of mainshock, are significantly larger than that at other places on the fault, which are spatially consistent with the Madoi earthquake series. Therefore, the tectonic stresses in high values are expected to be the main factor leading to the earthquakes. In addition, the stresses distributed on ground surface show high values along the Jiangcuo fault and spatially relate to the locations of surface ruptures, which indicates that the surface ruptures are mainly caused by the ground stress disturbances due to the mainshock and its aftershocks. Moreover, in terms of the tectonic stress distribution at the depth of hypocenter, the size of stress concentration region at the east section of the seismogenic fault is overwhelmingly larger than the area of aftershocks occupying, which implies that the Madoi earthquake might have only released part of the accumulated stress at the east section of the seismogenic fault. On basis of the trends of tectonic stress evolutions, we suggest that the southern east part of the Bayan Har block might be a potential seismic hazard zone in the future.

Automated summary

Based on the study of the 2021 Madoi earthquake, it was found that the tectonic stresses on the seismogenic fault and the ground stresses were correlated with the spatial distribution of the earthquake and the locations of surface ruptures. The Madoi earthquake may have only released part of the accumulated stress at the east section of the seismogenic fault. The southeastern part of the Bayan Har block may be a potential seismic hazard zone in the future.