SCEC Award Number 17085 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Dekameter-scale geologic structure validation of shallow seismic properties along the San Jacinto fault
Name Organization
Ramon Arrowsmith Arizona State University
Other Participants Collaboration with Yehuda Ben Zion (USC), Frank Vernon (UCSD/SIO), and Andrea Donnellan (JPL). ASU graduate student Adam Wade will be involved.
SCEC Priorities 1d, 2c, 3a SCEC Groups FARM, Seismology, SAFS
Report Due Date 06/15/2018 Date Report Submitted 11/12/2018
Project Abstract
Theoretical models of earthquake ruptures along a bi-material interface predict asymmetrical damage and preferred rupture propagation direction. The San Jacinto fault zone (SJFZ) in southern California provides an excellent forge for conducting geologic experiments on a young plate boundary, providing invaluable information on fault zone evolution and constraints on earthquake physics. Recent studies using a dense array of dense geophones deployed in a 10 m grid spacing along the Clark strand of the SJFZ at Sage Brush Flat (SGB), produced a high resolution seismic model of shallow fault zone structure and developed new techniques for seismic wave imaging and earthquake detection. We characterized the geology and structure imaged in the SGB dense array based on surface observations to help validate those from the dense array at a similar, dekameter, scale. Dissimilarities in geomorphology on opposite sides of the SJFZ are attributed to structural growth and fault zone damage. Spatial distributions of rock damage within SGB are primarily asymmetric with pulverization dominantly between fault strands or in the NE fault block. Observations from fault perpendicular transects depict an exhumed fault zone with complex structure and secondary high intensity rock damage roughly 70m from the main fault trace. Finally, a synthetic three-dimensional fault zone model illustrates the complexity of the structure at SGB for comparison with dense array seismology products.
Intellectual Merit This project contributed to our understanding of the relationship between the geologic structure as observed at the surface and the 3D seismic structure as characterized at depth. It showed that some of the simplified concepts of asymmetric damage may hold but the cumulative geologic history of deformation must be accounted for. Importantly, the work demonstrated a number of geological analyses and approaches which may have broad application for other similar geology-seismology characterizations of high resolution fault zone structure.
Broader Impacts This project represented a substantial labor by Mr. Adam Wade and comprised his M.S. thesis. It was part of a broader collaboration with Frank Vernon of Scripps, Yehuda Ben Zion of USC, and Andrea Donnellan of JPL. It provided an important benchmark and framework dataset for the SGB seismological dataset. Numerous papers will come from this work indirectly.
Exemplary Figure Figure 2-4: Geologic Map of SGB and surrounding areas. B4 hillshade basemap (Bevis et al., 2005) from Burnt Valley Road (NW) to Alkali Wash (SE). Fault trace mapping and nomenclature based on efforts from this study. Blue dots with yellow numbers indicate locations described in text and observed in figures 2-5 and 2-6 of the Wade thesis.