The San Andreas Fault revisited through seismic-noise and surface-wave tomography

Abstract

We present here surface-wave tomography results for the San Andreas Fault in the Parkfield area, California, USA, that were extracted from microseismic noise in the 0.15 Hz to 0.35 Hz frequency band using passive seismic-correlation techniques. Using directive noise incoming from the Pacific Ocean, passive seismic-noise tomography was performed using three-component sensors from a dense seismic network. A rotation algorithm was applied to the nine-component noise-correlation tensor that optimally forced each station pair to re-align in the noise direction, a necessary condition to extract unbiased travel-times from passive seismic processing. After the rotation was performed, an optimal surface-wave tensor is obtained from which Love waves were extracted for tomography inversion. Dispersion curves were then inverted to obtain a three-dimensional shear-velocity map showing vertical geological structures and a 1.3-km wide low seismic velocity dip, which are in agreement with previous tomography studies in the same area. Copyright 2011 by the American Geophysical Union.