SCEC Award Number 23045 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Bridging field, experimental, and geodetic observations to quantify co- and postseismic evolution of fault damage zones of the Ridgecrest earthquake sequence
Investigator(s)
Name Organization
Roland Bürgmann University of California, Berkeley Zachary Smith University of California, Berkeley
Other Participants
SCEC Priorities 2a, 3a, 3d SCEC Groups FARM, Geology, Geodesy
Report Due Date 03/15/2024 Date Report Submitted 03/14/2024
Project Abstract
 Determining how fault zone properties evolve and impact fault rupture over multiple earthquake cycles remains challenging. We combined geodetic, field, and laboratory observations of fault damage along distributed faults that ruptured during the 2019 Ridgecrest earthquake sequence to study how slip and off-fault deformation evolves through successive earthquake cycles. At Ridgecrest, 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 allow us to constrain slip and off-fault deformation due to a single event and the dikes enable us to constrain cumulative displacements. We use high resolution X-band COSMO-SkyMed (CSK) InSAR displacement maps to produce new fracture maps that highlight the complex network of faults in the Ridgecrest area. Geodetic results are compared to deformation in the field by collecting high resolution (mm scale) ground-based imagery and LiDAR over offset dikes which allows for an analysis of cumulative displacement and mesoscale fault damage properties (e.g., fracture density and fragment size). Results show damage asymmetry across faults which may result from preferred rupture directivity on subsidiary faults or by distributed off-fault shearing, as observed in geodetic studies. We explored how damage may evolve through multiple earthquake cycles by performing successive loading rock mechanics experiments. Integration of space geodetic and field observations provide a multiscale view of off-fault deformation to better inform the interpretation of strain in geodetic data and fault zone evolution.
Intellectual Merit Through this project we produced a new fracture map for the Ridgecrest area using COSMO-SkyMed InSAR which will improve our understanding of the complexity of earthquake rupture and contribute to our understanding of the hazards of earthquakes on distributed fault systems. This study improved our ability to interpret displacement fields obtained from InSAR by constraining fault zone properties using both field and experimental methods. We developed methods for using smartphone LiDAR and photogrammetry in sensitive areas near military bases to measure fracture density and fragment size around faults. From these scans we also produced high resolution digital surface models from which we can measure the impact of fault processes on topographic roughness. We performed rock mechanics experiments on rocks from Ridgecrest and advanced methods for dynamic tensile fragmentation by testing tin as a bounding metal for the layered tension experiment. This increased the range of strain rates for which we could measure the tensile strength and improved the safety of the experiments. This project included research that is pertinent to two of the SCEC5 basic questions of earthquake science including “Q2: What is the role of off-fault inelastic deformation on strain accumulation, dynamic rupture, and radiated seismic energy”, and “Q3: How do the evolving structure, composition and physical properties of fault zones and surrounding rock affect shear resistance to seismic and aseismic slip”. In addition, the aim of this study is aligned with areas of focus outlined in the 2023 RFP “New This Year” section including “near-fault studies for testing and developing further models of earthquake processes” and research on the Ridgecrest earthquake sequence. This work further improved the interpretation of high-resolution geodetic products and developed new methods for studying rock fragmentation using multiscale observations.
Broader Impacts This project supported the intellectual development of UC Berkeley PhD student Zachary Smith. In addition, this project supported an undergraduate researcher, Francis Waligora, who worked with Roland Bürgmann and Zachary Smith through the UC Berkeley Undergraduate Research Apprenticeship Program (URAP). The results of this study improved our understanding of the hazards of distributed faulting in the Ridgecrest, CA area and at the Naval Air Weapons Station China Lake.
Exemplary Figure Figure 1. Multiscale observations of fault zones around the 2019 Ridgecrest earthquake sequence ruptures. (A) New InSAR derived fracture map (yellow lines) using CSK data together with previously mapped fractures (Ponti et al., 2020; Xu et al., 2020a; Xu et al., 2020b; Rodriguez-Padilla et al., 2022). (B) Fracture density maps derived from iPhone-based imagery and LiDAR (see Figure 2 for transects). (C) Chlorite rich shear zone within the fault core of a ~100 m cumulative displacement fault. Rocks shown in (C) we used for rock mechanics experiments.
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