NSF Award
2422967
Determining processes that cause a fault to slip slowly (i.e., aseismically without earthquakes) or rapidly (i.e., seismically causing an earthquake) is a long-standing goal of the earth and ocean sciences. Oceanic transform faults offer a unique opportunity to study these underlying processes as transform faults accommodate plate motion through a combination of both aseismic and seismic slip. Several modeling studies and field-scale observations indicate that spatially variable material properties are correlated to differences in the slip behavior of oceanic transform faults. However, it is difficult to link these large-scale observations to experimentally derived rock material properties. This project will advance our understanding of the underlying controls on the slip behavior of oceanic transform faults by elucidating the links between material properties determined in the field and in laboratory settings. This project will also train an early career scientist and conduct outreach through a multi-institution virtual course on marine geology and geophysics.<br/><br/>Oceanic transform faults accommodate 85% of their slip aseismically, with earthquakes accommodating the remaining slip on discrete, localized fault patches. This project will determine how fault zone material properties control this variable slip behavior by analyzing crustal and upper mantle lithologies dredged from two oceanic transform faults: the slow-slipping Chain transform fault and the fast-slipping Gofar transform fault. Data on the petrophysical properties of these samples will be determined using various methods, including petrography, electron backscatter diffraction, micro-CT analysis, high-temperature pressure experiments, and effective medium modeling. Together, the results will provide insight into the petrophysical and elastic properties of fault zone materials, several at in-situ conditions, and address the following goals:<br/>● Elucidate the compositional controls, including the role of hydrothermal alteration, on slip behavior.<br/>● Decipher the role of fluids on slip behavior and the plausibility of dilatancy strengthening as a mechanism to prevent seismic slip.<br/>● Determine how strain is accommodated in different fault lithologies.<br/>● Characterize the geophysical signatures of crustal and upper mantle lithologies to aid in the interpretation of field-scale seismic data.<br/>A major societal benefit of this project will be an improved understanding of fault zone materials and their role in the complex dynamics of strike-slip fault systems.<br/><br/>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.
