CAREER: Shallow geophysics of fault creep: linking slip and surface deformation on the San Andreas fault

How active faults intersect with the Earth’s surface is critical for improving understanding of earthquake hazards, including anticipating where the surface will rupture in earthquakes, improving construction practices near faults, and for accurate estimation of fault slip rates, which is a fundamental input in seismic hazard models, used by insurance companies, government officials, land use managers, and private companies as well as in public outreach. However, the shallowest portion of the crust is poorly understood with respect to tectonic deformation and faulting. This CAREER project evaluates the relationship between tectonic faulting and near-surface deformation by investigating the creeping segment of the San Andreas fault in California. The lead researcher and team will image shallow fault structure with geophysical techniques coupled with satellite observations of active deformation. Field observations will guide computational models to explore links between creep and seismic faulting. This work will provide an increased near-field spatial resolution of fault behavior. The project leverages the strengths of California State University, Northridge (CSUN), to support robust tectonics and geophysics research opportunities, and apply research skills and tools to benefit local communities. In addition to supporting student research opportunities at CSUN, this project includes a pilot postdoctoral program to train a future professor at a teaching university. As part of student equipment training, the research team will conduct geophysical surveys and outreach in Magic Johnson Park in Watts, Los Angeles, in partnership with the Better Watts Initiative nonprofit organization. Due to the complex and spatially variable mechanical nature of the near-surface, the shallowest portion of the crust is poorly understood with respect to tectonic deformation and faulting. Characterizing how deformation intersects with the surface is critical for understanding the fundamental nature of faulting and ultimately for seismic hazard. This project will evaluate the relationship between tectonic faulting and near-surface deformation by interrogating shallow geophysics along the creeping segment of the San Andreas fault (SAF) in California (CA). The research team will image near-surface fault structure with Ground Penetrating Radar (GPR) and Electrical Resistivity Tomography (ERT) at 3 locations along the fault, spanning different bedrock and surface lithologies and a range of fault behavior from partial to full creep. The researchers will couple GPR and ERT imagery with observations of active deformation from GNSS to provide increased near-field spatial resolution of deformation partitioning in a way that is not possible on locked or deeper fault structures. As a creeping, relatively planar, vertical strike slip fault, the central SAF represents one of the simplest natural fault laboratories. Characterizing SAF creep in the near-surface establishes fundamental behavior with which to compare more complex faulting, including partial creep or locking on more complex fault geometries, at greater (i.e., seismogenic) depths. To guide such comparisons, mechanical modeling will establish possible parameters controlling creep partitioning that may illuminate links between creep and seismic faulting. This project is supported by the Geophysics program and Education and Human Resources program in the Division of Earth Sciences. 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.