Rupture dynamics and ground motion from 3‐D rough‐fault simulations

Abstract

AbstractWe perform three‐dimensional (3‐D) numerical calculations of dynamic rupture along non‐planar faults to study the effects of fault roughness on rupture propagation and resultant ground motion. The fault roughness model follows a self‐similar fractal distribution over length scales spanning three orders of magnitude, from ~102 to ~105 m. The fault is governed by a strongly rate‐weakening friction, and the bulk material is subject to Drucker‐Prager viscoplasticity. Fault roughness promotes the development of self‐healing rupture pulses and a heterogeneous distribution of fault slip at the free surface and at depth. The inelastic deformation, generated by the large dynamic stress near rupture fronts, occurs in a narrow volume around the fault with heterogeneous thickness correlated to local roughness slopes. Inelastic deformation near the free surface, however, is induced by the stress waves originated from dynamic rupture at depth and spreads to large distances (>10 km) away from the fault. The present simulations model seismic wave excitation up to ~10 Hz with rupture lengths of ~100 km, permitting comparisons with empirical studies of ground‐motion intensity measures of engineering interest. Characteristics of site‐averaged synthetic response spectra, including the distance and period dependence of the median values, absolute level, and intra‐event standard deviation, are comparable to appropriate empirical estimates throughout the period range 0.1–3.0 s. This class of model may provide a viable representation of the ground‐motion excitation process over a wide frequency range in a large spatial domain, with potential applications to the numerical prediction of source‐ and path‐specific effects on earthquake ground motion.