Dynamic Rupture and Seismic Radiation in a Damage–Breakage Rheology Model

Abstract

We present simulations of dynamic ruptures in a continuum damage–breakage rheological model and waves radiated by the ruptures and observed in the far field. The propagating rupture produces rock damage and granulation in the process zone ahead of the rupture front. An expansion–compaction process in the process zone leads to an isotropic source term, while shear motion that accumulates behind the propagating front produces a deviatoric source term and shear heating behind the rupture front. The process zone dissipation due to the damage–breakage mechanism, and the isotropic source component, significantly affect the S/P energy partitioning and the radiation patterns of the waves. The calculated S/P seismic energy ratio can be significantly lower than results of standard models with no damage–breakage mechanism and no source volume components. The P radiation pattern becomes more isotropic compared with the classical deviatoric solution, with increased lobes at 45° to the direction of rupture propagation. The S radiation pattern is affected more strongly by the damage–breakage process in the source volume, mainly within the process zone, and is significantly different from classical deviatoric results. The S waves propagate from the rupture front through the process zone (unlike the P waves), experiencing stronger dissipation, so the S radiation pattern is more affected than the P radiation pattern. Hence, analysis of P waves can provide more reliable results on rupture directivity than S waves.