Large-scale numerical simulations of earthquake fault systems: illuminating the role of dilatational gravity in earthquake nucleation

Simulated slip histories and the associated gravity changes were generated using a large-scale numerical simulation program for the San Andreas earthquake faults system, Virtual California. Statistical analysis of 55 000 years of these simulated earthquake cycles was investigated in order to study the usefulness of the dilatational gravity signal, those gravity changes due to a subsurface dilatational (or compressional) process, as a proxy for precursory stress and strain changes. Results indicate that the precursory dilatational gravity signal is dependent upon the fault orientation with respect to the tectonic loading plate velocity. This effect is interpreted as a consequence of preferential amplification of the shear stress or reduction of the normal stress, depending on the steady-state regime investigated. Copyright (c) 2009 John Wiley & Sons, Ltd.