Off-Fault deformation along the Superstition Hills and Elsinore Faults: Is there a fingerprint of Mmax preserved in fault damage zones?

Hannah E. Gaston, William A. Griffith, & Thomas K. Rockwell

Submitted September 11, 2022, SCEC Contribution #12555, 2022 SCEC Annual Meeting Poster #177

This study is driven by previous research that compares the fracture energy (G) for both laboratory and natural earthquakes, where energy for earthquakes smaller than Mw6.6 is dissipated primarily by frictional heating. Earthquakes larger than Mw6.8 have additional dissipated energy that may be explained by inelastic off-fault deformation. We investigate this hypothesis by comparing two fault damage zones in Southern California. The Superstition Hills and Elsinore faults have hosted recent earthquakes on the order of Mw6.6 and Mw6.8, respectively, in the last 300 years. Despite belonging to the same tectonic environment and occurring in similar lithologies, the damage zones exposed in outcrops along these faults differ in size, fracture density, and scale. We studied damage zone fractures in sandstones of the Imperial formation at the Elsinore fault in Fossil Canyon. Macroscopic damage is in the form of several sets of deformation bands where the density does not decay with distance from the principal slip zone. Rather, deformation bands cluster around smaller faults in the damage zone. In contrast, microstructural damage at the sub-grain scale is pervasive in the bulk rock, and damage intensity decays with distance from the fault. For comparison, we studied the damage zone of the Superstition Hills Fault in the Palm Spring formation which consists of poorly to well-indurated non-marine sandstones at Imler Road. Here, the macroscopic damage occurs as one dominant set of primarily opening-mode fractures that decay in intensity with distance from the fault. At the microscopic scale, damage zone rocks at the Imler Road outcrops display negligible damage. We discuss these observations and their potential implications for understanding how deformation is partitioned across the fault damage zone through space and time, the potential roles of fault geometry, seismic rupture, and burial depth, and the ultimate goal of estimating Mmax from damage zone observations.

Key Words
Elsinore Fault, Superstition Hills fault, off-fault deformation, fault damage zones, fracture density

Gaston, H. E., Griffith, W. A., & Rockwell, T. K. (2022, 09). Off-Fault deformation along the Superstition Hills and Elsinore Faults: Is there a fingerprint of Mmax preserved in fault damage zones?. Poster Presentation at 2022 SCEC Annual Meeting.

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