High-resolution Imaging of Complex Shallow Fault Zones Along the July 2019 Ridgecrest Ruptures

Zheng Zhou, Michael J. Bianco, Peter Gerstoft, & Kim B. Olsen

Accepted December 10, 2021, SCEC Contribution #11761

We perform ambient noise tomography (ANT) using data recorded on 342 seismographs within a 50 km x 50 km area inside which the July 2019 M7.1 and M6.4 Ridgecrest earthquakes occurred. We used the locally sparse tomography (LST) method, an unsupervised machine learning approach that learns to represent small-scale geophysical structures using only data from the immediate study. The Rayleigh group speed obtained from LST better predicts travel times than conventional regularized least-squares inversion. The 3D shear velocity model of the area obtained from the surface wave dispersion maps reveals a highly heterogeneous low-velocity zone (LVZ, with the primary velocity reduction in the upper 2-3 km) around the causative faults for the M7.1 and M6.4 events, with a 40% reduction of the shear wave velocity. Further, correlation of other imaged LVZs in the model area with parts of the Little Lake Fault System without recent activity may indicate long-lasting damage zones.

Citation
Zhou, Z., Bianco, M. J., Gerstoft, P., & Olsen, K. B. (2021). High-resolution Imaging of Complex Shallow Fault Zones Along the July 2019 Ridgecrest Ruptures. Geophysical Research Letters, (accepted).