Regularization effect in rupture dynamics along bimaterial interface

Faults separating materials with different elastic properties are common in nature. Ruptures along such bimaterial interface may have favored propagation direction and asymmetric near surface damage distribution, as sometimes observed along the San Andreas and Anatolian faults. To explore rupture behaviors along bimaterial interfaces, numerical simulations of dynamic rupture process provide useful tools. However, the coupling between slip rate and normal stress perturbations requires a regularization process to avoid an instantaneous proportionality between shear and normal stress, and the resultant grid dependence of the numerical results. We numerically investigate the slip rates and normal stress distributions in a vertical strike-slip fault separating dissimilar materials with a parametric study using the Prakash-Clifton form of regularization. The effects of constant and dynamic relaxation time are examined. The oscillations of normal stresses, which are more significant in the positive (i.e., most favored) rupture direction are greatly reduced with the regularization process. In some cases, slip rate amplitude can be strongly affected by the choice of regularization parameter, even while the rupture velocity is relatively unaffected. This study provides useful insights to guide the choice of regularization parameters for dynamic models of bimaterial faults.