Zhenguo Zhang

Earthquake rupture extents and coseismic slips promoted by damaged fault zones

Here we investigate the effects of damage fault zones on rupture propagation by conducting a series of 3-D dynamic rupture simulations on a planar vertical strike-slip fault. We find that damage fault zones can promote rupture extent and increase earthquake potency. The waves reflected from the bottom of shallow damage fault zones can increase shear stress on the fault and thus promote rupture propagation. In addition, the promotional effects increase with the width and depth extent of damage fault zones. The overall effects of the waves reflected from the fault-parallel side boundaries of damage fault zones are unfavorable for rupture propagation. Therefore, rupture propagation is promoted with the increased width of fault zones due to geometrical spreading effects. Moreover, nonground-breaking ruptures may reach the ground surface with the effects of damage fault zones. Furthermore, along-strike segmented fault zones as suggested by observations could also promote ruptures and may lead to preferred rupture directions if epicenters are close to fault zones. The effects of damage fault zones on rupture propagation hold important implications on assessing earthquake risk.

On the Free‐Surface Problem in Dynamic‐Rupture Simulation of a Nonplanar Fault

Abstract Spontaneous dynamic‐rupture simulation in 3D is a difficult task in seismology, especially for the rupture dynamics of a fault with complex geometry and a free surface. In this study, we model an irregular fault that reaches the free surface and investigate the rupture dynamics of the intersection between the earthquake‐induced fault and the Earth’s surface. We use the recently proposed curved grid finite‐difference method (CG‐FDM) to simulate a spontaneous dynamic rupture. However, this involves solving the inversion of an ill‐conditioned matrix that is required in finite‐difference method modeling at the point of intersection, which must be addressed to achieve stable simulation conditions. We achieve stable conditions at the intersection between the fault plane and the free surface by considering the continuity of the fault’s normal displacement, ensuring that the point of intersection meets the conditions of both the fault and the free surface. To verify our method, we simulate the spontaneous dynamic rupture of a rough fault in half‐space and compare the results with those from another method. The good agreement between two methods validates our mathematical strategy for modeling the intersection between an irregular fault plane and a free surface using CG‐FDM.