Collaborative Research: Identifying shallow slow slip using hematite textures and (U-Th)/He thermochronometry of exhumed and experimental faults

Slow slip, the movement along a fault without an earthquake, is a fundamental part of the seismic cycle. In the near-surface environment, slow slip may impact a range of tectonic processes and seismic hazards, including reducing earthquake energy, controlling how earthquakes stop, and the intensity of ground shaking. A critical unknown is how the material properties of fault rocks control this phenomenon.

This project focuses on a segment of the San Andreas fault that is overdue for a large earthquake and has experienced recent slow slip events. Investigators will make use of the unique textural and geochemical qualities of hematite, a common mineral in faults, to determine the prevalence, timing, and impact of slow slip along the southern San Andreas fault in Mecca Hills, California.

Comparison of observations from natural hematite-coated faults with laboratory deformation experiments will document how hematite deforms to understand what governs where and why slow slip occurs. Data will be integrated into a new educational program, the Providence (Utah) to Providence (Rhode Island) Partnership, that will connect rural and urban students in different parts of the country and impact more than 450 elementary and middle school students.

Research and broader impact activities will provide mentoring and role modeling opportunities for middle school through faculty levels, critical for expanding and diversifying the sciences through each stage of education and training.

Hematite is a common mineral on fault surfaces and its textures and thermochronometry data patterns can characterize a range of fault behavior. This project tests the hypothesis that hematite on fault surfaces promotes shallow slow slip by comparing data from hematite-coated slip surfaces in upper crustal, bedrock fault damage zones from Mecca Hills, with results from deformation experiments at sub-seismic slip rates on both hematite gouge and natural fault surfaces.

Multi-scale microscopy and spectroscopy of hematite (and comparisons to clay textures), hematite (U-Th)/He analyses, and 4He/3He thermochronometry will be used to investigate rate-dependent friction behavior of hematite, related fault slip temperatures, deformation mechanisms, and spatiotemporal patterns of past shallow fault slip. This research will generate bedrock material property data that are critical for realistic physics-based models integrating shallow slow slip into the seismic cycle.

The Providence to Providence Partnership will connect eighth graders at the Center for Creativity, Innovation, and Discovery in rural Utah, situated in the Intermountain Seismic Belt, with fourth graders in urban Rhode Island, via Zoom teleconferences. Researchers and students will engage in annual virtual and field education modules on faults and earthquakes.

Eighth graders in Utah will teach these concepts to rising Utah eighth graders and fourth graders in RI. This project also provides training and support for graduate and undergraduate researchers, as well as a postdoctoral fellow.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.