Lawrence Berkeley National Laboratory

We provide high-resolution seismic imaging of the central Garlock fault using data recorded by two dense seismic arrays that cross the Ridgecrest rupture zone (B4) and the Garlock fault (A5). Analyses of fault zone head waves and P-wave delay times at array A5 show that the Garlock fault is a sharp bimaterial interface with P waves traveling ∼5% faster in the northern crustal block. The across-fault velocity contrast agrees with regional tomography models and generates clear P-wave reflections in waveforms recorded by array B4. Kirchhoff migration of the reflected waves indicates a near-vertical fault between 2 and 6 km depth. The P-wave delay times imply a ∼300-m-wide transition zone near the Garlock fault surface trace beneath array A5, offset to the side with faster velocities. The results provide important constraints for derivations of earthquake properties, simulations of ruptures and ground motion, and future imaging studies associated with the Garlock fault.