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Off-Fault Deformation Along the Superstition Hills and Elsinore Faults: A Moment-Dependent Bifurcation in Off-Fault Energy Dissipation Processes?

Gaston, Hannah E
http://rave.ohiolink.edu/etdc/view?acc_num=osu1672825340413263

Abstract Details

2023, Master of Science, Ohio State University, Earth Sciences.
Faults are structural discontinuities in the upper crust that are responsible for earthquake hazards. The damage zone that surrounds faults consist of a complex network of brittle structures (e.g., fractures) that can extend up to several hundred meters from the principal slip zone along large mature faults. These structural features potentially hold information about faulting processes and could be useful in probabilistic seismic hazard assessments. One key clue that the structure of fault damage zones may hold information regarding the potential size of future earthquakes comes from a comparison of facture energy (G) measured from laboratory rotary shear experiments and natural earthquakes (Nielsen et al., 2016). Whereas these numbers are equivalent for small earthquakes, G for large natural earthquakes far exceeds that of laboratory measurements for equivalently sized events, causing seismologists to speculate that a significant portion of the earthquake energy budget for large earthquakes is dissipated in permanent off-fault deformation. These seismologists have posited that across the moment magnitude range (e.g., Mw6.6-6.8), the earthquake energy budget undergoes an important transition wherein energy dissipation by inelastic off-fault damage constitutes an increasingly significant fraction of the total breakdown energy (Nielsen et al., 2016). In this thesis, I attempt to investigate this hypothesis by examining the damage zones along two faults in Southern California: the Elsinore and Superstition Hills Fault. These faults have hosted recent earthquakes of approximately to Mw6.8 and Mw6.6 respectively. The damage zones surrounding these faults differ significantly in size and fracture density despite belonging to the same tectonic environment and being formed in similar sandstone lithologies. We conducted fieldwork near the entrance to Fossil Canyon in the Coyote Mountains where the Elsinore Fault crosses the Imperial Formation and at Imler Road where the Superstition Hills Fault crosses the Palm Spring Formation. Locally, the Palm Spring Formation largely consists of poorly lithified non-marine sandstones that are thinly interbedded with strongly indurated sandstone. Comparatively, the Imperial Formation consists of solidified fossiliferous sandstones. We studied the mesoscale damage fractures up to 125m from the Superstition Hills Fault and up to 300m from the Elsinore Fault by constructing highresolution photomosaics. The photomosaics used to map fractures showed the damage zone at the Elsinore Fault is expressed as deformation bands that form clusters around small faults. Brittle damage in the Superstition Hills Fault is expressed a single systematic set of joints. Additionally, we studied the microstructural damage zone of these two faults by collecting samples for microstructural analysis. At the microscopic scale, the Superstition Hills Fault shows no apparent deformation in the damage zone. In comparison, the Elsinore Fault shows significant damage close to the principal slip zone which consistently decreases until 40m where the damage slowly tapers off. I use observations at both the outcrop and microstructural scales to discuss the differences in the damage zone structures and the potential of these observations to learn about past earthquakes and the resulting off-fault deformation.
William Griffth (Advisor)
Derek Sawyer (Committee Member)
Wendy Panero (Committee Member)
126 p.
Earth; Geology
Elsinore Fault Coyote Mountains Superstition Hills Fault Imler Road Fault Damage Zone Deformation Bands Fracture Density Earthquakes

Recommended Citations

Citations

  • Gaston, H. E. (2023). Off-Fault Deformation Along the Superstition Hills and Elsinore Faults: A Moment-Dependent Bifurcation in Off-Fault Energy Dissipation Processes? [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1672825340413263

    APA Style (7th edition)

  • Gaston, Hannah. Off-Fault Deformation Along the Superstition Hills and Elsinore Faults: A Moment-Dependent Bifurcation in Off-Fault Energy Dissipation Processes? 2023. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1672825340413263.

    MLA Style (8th edition)

  • Gaston, Hannah. "Off-Fault Deformation Along the Superstition Hills and Elsinore Faults: A Moment-Dependent Bifurcation in Off-Fault Energy Dissipation Processes?" Master's thesis, Ohio State University, 2023. http://rave.ohiolink.edu/etdc/view?acc_num=osu1672825340413263

    Chicago Manual of Style (17th edition)

osu1672825340413263
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