SCEC Award Number 22116 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Damage zone of the Coachella Valley segment of the San Andreas Fault: Evidence of a moment-dependent bifurcation in off fault energy dissipation processes?
Name Organization
William Griffith Ohio State University
Other Participants Thomas Rockwell, San Diego State University
1 graduate student, Ohio State University
1 undergraduate or graduate field assistant, Ohio State University
SCEC Priorities 3d, 3c, 3e SCEC Groups Geology, FARM, SDOT
Report Due Date 03/15/2023 Date Report Submitted 03/17/2023
Project Abstract
i. We proposed to conduct an initial test of the hypothesis that energy dissipation by inelastic off-fault deformation increases dramatically above Mw 6.6-6.8.
ii. To this end, in previous work, we conducted field work in June 2021 and November 2021 to map fault damage zones along the Elsinore and Superstition Hills Faults, measure mesoscopic (outcrop-scale) fracture density and orientation data at varying distances from the fault core, and we collected oriented samples for thin section analysis of microstructure at similar positions.
iii. Under this grant, we spent two weeks in the field, excavating fresh outcrop surface along a 100m transect across the SSAF at Ferrum in an abandoned turnaround wye. We collected 23 oriented samples and 25 unoriented samples, and we built several high resolution 3D photomosaics to characterize the damage zone structure.
iv. Initial observations show the damage zone structure is asymmetric about the fault. The southwest side of the fault consists of a 15m wide foliated shear zone, outside of which rocks are extensively faulted in a jigsaw pattern. A pulverized granite pod is located about 40 m SW of the fault. On the opposite side of the fault, deformation is confined primarily to thin shear zones subparallel to the main fault strand.
v. We proposed to continue this work in a 2023 proposal by complementing our outcrop observations with a suite of geochemical analyses. We are also planning a NSF-UKNERC proposal this spring based on SCEC-funded research during the past three years.
Intellectual Merit The Intellectual Merit of this project is the potential for developing an independent, deterministic criterion for Mmax on active faults by examining the damage zone structure and using rock mechanics experiments to link field-based observations to physics-based models of rock deformation.
Broader Impacts The Broader Impacts lie in large part in the development of an independent check on Mmax determined by other methods for PSHA, particularly for faults for which little is known about seismic history, overall fault geometry, or slip rate. This project has supported the research of new PhD student, Aidan Fullriede, at Ohio State University.
Exemplary Figure Figure 4: Summary of observations from SSAF in turnaround wye at Ferrum. (A) Overview of outcrop from 3D model showing primary fault (NE), secondary fault (SW), bedding (green lines), outline of detailed photomosaic and outcrop log, and locations of images in B-D. (B) Jigsaw fractures in sandstones (left of hammer) contrasted against distributed shearing in claystones (right of hammer), (C) Strongly foliated zone adjacent to fault core, (D) Pulverized granite.