Lateral P-Velocity Gradients near Major Strike-Slip Faults in California.

TLDR: The P-wave velocity in shallow crystalline rock decreases systematically from a normal value from the Garlock and San Andreas faults to less than 3 kilometers per second at distances of less than 2 kilometers from these faults, which closely resembles the shear stress profile.

Abstract: The P-wave velocity in shallow crystalline rock decreases systematically from a normal value of about 5.5 kilometers per second 20 kilometers or more from the Garlock and San Andreas faults to less than 3 kilometers per second at distances of less than 2 kilometers from these faults. This lateral velocity gradient closely resembles the shear stress profile. It is proposed that the velocity gradient results from increased fracturing nearer these major strike-slip faults and that this fracturing dominates the response of the shallow crust to tectonic stress.