Constraining depth range of S wave velocity decrease after large earthquakes near Parkfield, California

We use noise correlation and surface wave inversion to measure the S wave velocity changes at different depths near Parkfield, California, after the 2003 San Simeon and 2004 Parkfield earthquakes. We process continuous seismic recordings from 13 stations to obtain the noise cross‐correlation functions and measure the Rayleigh wave phase velocity changes over six frequency bands. We then invert the Rayleigh wave phase velocity changes using a series of sensitivity kernels to obtain the S wave velocity changes at different depths. Our results indicate that the S wave velocity decreases caused by the San Simeon earthquake are relatively small (~0.02%) and access depths of at least 2.3 km. The S wave velocity decreases caused by the Parkfield earthquake are larger (~0.2%), and access depths of at least 1.2 km. Our observations can be best explained by material damage and healing resulting mainly from the dynamic stress perturbations of the two large earthquakes. Key Points S wave velocity decrease of ~0.02% after the 2003 San Simeon earthquake and ~0.2% after the 2004 Parkfield earthquake The minimum depth extent of velocity decrease is ~2.3 km for the San Simeon earthquake and ~1.2 km for the Parkfield earthquake Best explained by material damage and healing resulting mainly from dynamic stress perturbation of the two large earthquakes