Epicentral location based on Rayleigh wave Empirical Green's Functions from ambient seismic noise

SUMMARY A new method to locate the epicentre of regional seismic events is developed with strengths and limitations complementary to existing location methods. This new technique is based on applying empirical Green's functions (EGFs) for Rayleigh waves between 7 and 15 s period that are determined by cross-correlation of ambient noise time-series recorded at pairs of seismic receivers. The important advantage of this method, in comparison with standard procedures based on use of body wave traveltimes, is that it does not rely on an earth model. Rather it is based on interpolating the EGFs to arbitrary hypothetical event locations. The method is tested by locating well known ‘Ground Truth' crustal events in the western United States (magnitude 4 earthquakes in California, magnitude 3 earthquakes in Utah, and a mine collapse) as well as locating seismic stations as virtual events. In these applications, location errors average less than 1 km, but are expected to vary with event mechanism and depth. Numerical simulations show that the method optimizes when source depth is less than 1 km or more than 5 km, and when the source mechanism is nearly purely strike-slip, thrust or normal.