Abstract

Multi-scale seismic imaging of fault zones and the surrounding crust reveal hierarchical rock damage around large fault zones with intense core damage zones and bimaterial interfaces with 5-10% velocity contrasts that may be the primary failure surfaces of ruptures. The fault damage zones follow a flower-shape structure, with significant damage in the top few km that decreases in amplitude and width with depth, and they tend to be offset from the surface trace to the side with higher seismic velocity at depth. The top 50-100 m section has typically extreme seismic properties (very low Vp, Vs, Q values; very high Vp/Vs ratios) that make it, together with the low normal stress, highly susceptible to failure and temporal changes. The detailed local imagining results are merged with regional velocity models to provide multi-scale models that can be used to simulate ground motion from large scenario earthquakes and other applications.