Effects of seismogenic width and low-velocity zones on estimating slip-weakening distance from near-fault ground deformation
Xiang Chen, Hongfeng Yang
Abstract
SUMMARY Fault weakening process controls earthquake rupture propagation and is of great significance to impact the final earthquake size and seismic hazard. Critical slip-weakening distance (${D_c}$) is one of the key parameters, which however is of difficult endeavours to be determined on natural faults, mainly due to its strong trade-off with the fault strength drop. An estimation method of ${D_c}$ proposed by Fukuyama et al. provides a simple and direct reference of ${D_c}$ on real faults from the near-fault ground displacement at the peak of ground velocity (${D_c}^{\prime\prime}$). However, multiple factors may affect the observed near-fault ground velocity and thus need to be considered when estimating ${D_c}.$ In this work we conduct 3-D finite element numerical simulations to examine the effects of finite seismogenic width and near-fault low velocity zones (LVZs) on the results of ${D_c}^{\prime\prime}$. In uniform models with constant prescribed ${D_c}$, the derived ${D_c}^{\prime\prime}$ values increase with seismogenic width. Furthermore, the scaling between ${D_c}^{\prime\prime}$ and final slip in models with a constant ${D_c}$ indicates that the scale-dependent feature of ${D_c}^{\prime\prime}$ might not be related to variation in friction properties. With a near-fault LVZ, ${D_c}^{\prime\prime}$ values show significant magnification. The width of the LVZ plays a more important role in enlarging ${D_c}$ estimation compared to the depth of the LVZ. Complex wavefields and multiple wiggles introduced by the LVZ could lead to delay pick and then cause large deviation. The value of ${D_c}$ on the fault may be overestimated through ${D_c}^{\prime\prime}$ from limited stations only.