Locating earthquakes with surface waves and centroid moment tensor estimation

Abstract

Traditionally, P wave arrival times have been used to locate regional earthquakes. In contrast, the travel times of surface waves dependent on source excitation and the source parameters and depth must be determined independently. Thus surface wave path delays need to be known before such data can be used for location. These delays can be estimated from previous earthquakes using the cut-and-paste technique, Ambient Seismic Noise tomography, and from 3D models. Taking the Chino Hills event as an example, we show consistency of path corrections for (>10 s) Love and Rayleigh waves to within about 1 s obtained from these methods. We then use these empirically derived delay maps to determine centroid locations of 138 Southern California moderate-sized (3.5 > M_w > 5.7) earthquakes using surface waves alone. It appears that these methods are capable of locating the main zone of rupture within a few (~3) km accuracy relative to Southern California Seismic Network locations with 5 stations that are well distributed in azimuth. We also address the timing accuracy required to resolve non-double-couple source parameters which trades-off with location with less than a km error required for a 10% Compensated Linear Vector Dipole resolution.