Off-fault damage accumulation and evolution in distributed fault systems near Ridgecrest, CA

Zachary D. Smith, Roland Bürgmann, William A. Grifith, Mengsu Hu, & Michael Manga

Published September 10, 2023, SCEC Contribution #13007, 2023 SCEC Annual Meeting Poster #133

Fault zones consist of numerous subsidiary faults surrounding large displacement faults. Individual subsidiary faults are often enveloped by damage zones on the scale of centimeters to meters making large fault zones heterogeneous. As space geodetic and seismic observations improve, the structural heterogeneity of upper crustal fault damage zones is being revealed. Nonetheless, the impact of distributed heterogeneous fault zones on the stress state around faults and earthquake source properties remains uncertain. We combine observations from geodetic and field studies with 3-D discrete element modeling (DEM) to evaluate the relationship between slip and off-fault deformation on subsidiary faults. Our study is focused on distributed faults that ruptured during the 2019 Ridgecrest earthquake sequence. Coseismic surface offsets are well imaged by satellite observing systems and the faults cut dikes of the extensive Independence dike swarm which serve as excellent linear cumulative displacement markers exposed at Earth’s surface. Geodetic observations constrain slip and off-fault deformation due to a single event and the dikes enable us to constrain cumulative displacements. We use co- and postseismic high resolution X-band COSMO-SkyMed (CSK) InSAR and existing Sentinel-1 InSAR and optical image correlation results to compare slip and off-fault damage on numerous faults. We compare deformation observed geodetically to observations of deformation in the field including high resolution mesoscale brittle fault damage properties (e.g., fracture density and fragment size). Results show lithology independent damage asymmetry across faults which may result from preferred rupture directivity on subsidiary faults or distributed off-fault shearing, as observed in geodetic studies. 3-D numerical modeling of loading within distributed fracture networks reveals that slip is concentrated and maintained on the most optimally oriented primary fault even in the presence of intense off-fault fracture networks. However, as slip continues the stress state may evolve impacting the slip behavior on both primary and subsidiary faults. Integration of geodetic and field observations with 3-D DEM provides a multiscale view of off-fault deformation to better inform the interpretation of inelastic strain accumulation in geodetic data, damage accumulation along large strike-slip faults, and seismic hazards associated with distributed shallow faulting.

Key Words
Fault Damage, Rupture Directivity, Ridgecrest

Citation
Smith, Z. D., Bürgmann, R., Grifith, W. A., Hu, M., & Manga, M. (2023, 09). Off-fault damage accumulation and evolution in distributed fault systems near Ridgecrest, CA. Poster Presentation at 2023 SCEC Annual Meeting.

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