Off-Fault Damage Characterization in the Damage Zone of the Coachella Segment of the Southern San Andreas Fault, California

Aidan Fullriede, William A. Griffith, & Thomas K. Rockwell

Published September 10, 2023, SCEC Contribution #13097, 2023 SCEC Annual Meeting Poster #097

Evidence from laboratory earthquake experiments, observational seismology, and theoretical fracture mechanics suggest that inelastic off-fault deformation may be significantly more extensive for large earthquakes than small events. This begs the question of whether or not we can determine the seismic potential of active fault zones by examining properties of their damage zones. Faults accrue off-fault damage throughout their evolution via a number of different mechanisms that can be loosely grouped into quasi-static mechanisms (related to slow, long-term processes involved in fault growth), to dynamic mechanisms related to earthquake rupture. We have studied damage zones along the Superstition Hills, Elsinore, and San Andreas faults – faults that have hosted Mw 6.6, Mw6.8, and ~Mw7.4 events respectively in the last few hundred years – to categorize the style of off-fault damage where the faults cut similar lithologies. We report here the work done under Award #22116 along the Coachella segment of the southern San Andreas Fault at a field site located along the Ferrum, CA railroad wye. We spent 2 weeks performing field work, during which we excavated a ~100m transect perpendicular to the southern San Andreas fault. We created an annotated 3D photomosaic of the outcrop using drone photography and collected 23 oriented samples and 22 bagged samples throughout the transect, including the fault core. Here, we present the structural data, detailed rock and thin section descriptions, and preliminary powdered x-ray diffraction results from our samples throughout the damage zone transect.

Citation
Fullriede, A., Griffith, W. A., & Rockwell, T. K. (2023, 09). Off-Fault Damage Characterization in the Damage Zone of the Coachella Segment of the Southern San Andreas Fault, California. Poster Presentation at 2023 SCEC Annual Meeting.

Related Projects & Working Groups
San Andreas Fault System (SAFS)