Does Slip Heterogeneity Drive Near-field Fracture and Aftershock Distribution? Examples from the 2019 Ridgecrest Sequence

Alba M. Rodriguez Padilla, Michael E. Oskin, & Chris Milliner

Published August 14, 2020, SCEC Contribution #10578, 2020 SCEC Annual Meeting Poster #138

The 2019 Ridgecrest earthquake sequence ruptured a set of orthogonal faults in the best monitored continental earthquake sequence to date. A year after the event, numerous high-resolution products capturing the sequence are publicly available, including a high-resolution earthquake catalog, a detailed map of field-measured offsets, 50-cm-per-pixel lidar data, SAR interferometry, and cross-correlated satellite imagery. This excellent spatiotemporal coverage offers the opportunity to assess the contribution of variations of coseismic slip along the rupture to the generation of distributed fractures and triggering of aftershocks at shallow depths. We compare the spatial distribution of on-fault slip and off-fault displacement gradients to the distribution of surface fractures and aftershocks to assess the role of slip heterogeneity in driving brittle deformation. We use on-fault measurements of surface slip and distributed deformation derived from optical image correlation, and compare these to fracture density and orientation mapped from lidar, and aftershock distribution from the Ridgecrest QTM catalog. Surficially expressed fractures and aftershock (<5 km depth) density show moderate to strong correlation with the exception of the middle section of the mainshock rupture. The majority of the surface fractures correspond to areas of extensional strain and cluster in areas with strong displacement gradients regardless of displacement magnitude. Preliminary results suggest that slip gradients on-fault trade-off with sections of increased distributed deformation and diffuse aftershock distribution along the rupture, and that strong slip gradients spatially correlate to areas of dense surface fracturing and increased rupture complexity.

Key Words
Stress Heterogeneity, Brittle Failure, Coseismic Deformation, Postseismic Deformation

Citation
Rodriguez Padilla, A. M., Oskin, M. E., & Milliner, C. (2020, 08). Does Slip Heterogeneity Drive Near-field Fracture and Aftershock Distribution? Examples from the 2019 Ridgecrest Sequence. Poster Presentation at 2020 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)