Evaluation of Connectivity Between Ridgecrest Faults and the Garlock Fault Using PGV of Guided Waves

Abstract:

From aftershocks of the 2019 Ridgecrest earthquake sequence, we provide evidence for connectivity of the two causative faults and the Garlock Fault by examining peak ground velocities (PGV) of guided waves recorded on all three faults. The Mw 6.4 Ridgecrest earthquake occurred on a NE-SW-trending fault, and the Mw 7.1 Ridgecrest earthquake occurred ~1 day later on an orthogonal NW-SE-trending fault, with surface ruptures from the two earthquakes crossing at nearly right angles. Aftershocks and surface ruptures along both faults project toward segments of the Garlock Fault. On the NW-SE-trending Ridgecrest fault, surface ruptures extended ~50 km, ending about 5 km from the intersection with the Garlock Fault, but aftershocks extended to the Garlock Fault. Along the NE-SW-trending Ridgecrest fault, surface ruptures extended ~20 km, ending about 20 km from the intersection with the Garlock Fault. Although a few aftershocks along the NE-SW-trending fault appear to have extended to the Garlock Fault, the majority of aftershocks ended about 15 km from the intersection of the two faults. Aftershocks on both the NE-SW- and the NW-SE-trending faults generate high PGV of guided wave values along the Garlock Fault, suggesting all three faults are connected at depth. Such connectivity, combined with the observed sequence of ruptures on the Ridgecrest faults in 2019, indicates that rupture on any one of the three faults (NW-SE, NE-SW, and Garlock) may strongly affect the potential for rupture on the other two faults. We found high PGV of guided wave values to coincide with mapped surface ruptures of the Ridgecrest faults, which are distributed over wide zones (~5 km), but high PGV values on the Garlock Fault appear more concentrated, occurring over widths of less than 1 km at our recording array. The concept of a more concentrated zone of slip on the Garlock Fault may imply that the Garlock Fault is a more mature fault that ruptures easier than the Ridgecrest faults.