Study of fault zone damage and healing in the 2019 Ridgecrest aftershock sequence

Wei Wang, & John E. Vidale

Published August 14, 2020, SCEC Contribution #10539, 2020 SCEC Annual Meeting Poster #069

The structure and evolution of faults is a key to understanding earthquake fault systems and the earthquake cycle. By velocity weakening and strain localization, faults generate earthquakes from plate motions. One outstanding question is just how faults weaken as they break, and then re-strengthen afterwards. Faults may heal through a variety of processes – deformation, closure of cracks by indentation, sealing of cracks by chemical processes, or redistribute fluids, for example.

The 2019 Ridgecrest earthquakes occurred near the town of Ridgecrest, southeast of CGF, including an M6.4 foreshock on July 4 and the M7.1 mainshock on July 6. After Ridgecrest earthquake, four dense linear arrays were deployed across the fault zone of M7.1 mainshock and one deployed across the fault zone of M6.4 foreshock. The repeating earthquakes have very similar focal mechanisms and locations, but occur at different times, allowing study of the temporal changes of the media. In this study, we are using repeating earthquakes to detect and track through time the damage and healing of the Ridgecrest fault zone and its wallrock through the change in P and S velocities, and map its vertical and lateral distribution.

Initial results show clear 0.01 to 0.02s changes in the arrival times of P and S waves in the days after the mainshocks, and more complex spatial patterns for shallow (~3 km) than deep (~10 km) earthquakes. Changes in stations a few km off the fault trace indicate the velocity changes are not restricted to just the core of the fault zone. We aim to understand the relation between the slip and damage, with an emphasis on the temporal variations that constrain the recovering process of the fault zone damage.

Key Words
Fault zone, Temporal change, Repeating earthquakes

Citation
Wang, W., & Vidale, J. E. (2020, 08). Study of fault zone damage and healing in the 2019 Ridgecrest aftershock sequence. Poster Presentation at 2020 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology