Ambient noise-based monitoring of seismic velocity changes associated with the 2014 Mw 6.0 South Napa earthquake

We perform an ambient noise-based monitoring to explore temporal variations of crustal seismic velocities before, during, and after the 24 August 2014 M-w 6.0 South Napa earthquake. A velocity drop of about 0.08% is observed immediately after the South Napa earthquake. Spatial variability of the velocity reduction is most correlated with the pattern of the peak ground velocity of the South Napa mainshock, which suggests that fracture damage in rocks induced by the dynamic strain is likely responsible for the coseismic velocity change. About 50% of the velocity reduction is recovered at the first 50 days following the South Napa mainshock. This postseismic velocity recovery may suggest a healing process of damaged rocks.