Investigation of the hydrogeologic role of faults in the downgoing plate through comparison of Central America, Cascadia, Nankai, and Alaska subduction zones

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Part 1The award will fund a GeoPRISMS postdoctoral Fellowship for two years of training at the University of Texas, Institute for Geophysics (UTIG). The proposed work seeks to quantitatively determine the structure and water content in the faults within the select segments of the subducting plates. This will allow the assessment of the effects of subducting water on subduction zone processes. The study will use existing 2D and 3D multichannel seismic data from Central America, Cascadia, Nankai, and Alaska subduction zones. The results will provide a better understanding of the geohazard potential in subduction zones, which is particularly relevant for the Pacific Northwest region where large magnitude earthquakes have occurred on the Cascadia megathrust in recent history. The postdoctoral fellow is an early-career female scientist. The results of the study will be presented at workshops and conferences and will contribute to the high school curriculum development program at UTIG. Part 2Funds are provided for a postdoctoral fellow to conduct amplitude preserved seismic prestack depth migration, 2D waveform modeling of fault plane reflections, and fluid flow modeling of the 2D multichannel seismic data at Nicaragua, Cascadia, Nankai, and Alaska subduction zones to explore the limits on the water content of the fault zones in the oceanic plate seaward of the trench. From these results she will begin to quantitatively assess the hydration state of incoming plate at different subduction zones. The seismic attribute analysis of decollement, near-basement sediment, and basement crustal rocks, and the waveform modeling of the faults in the down-going plate beneath the slope in Nankai and Costa Rica 3D datasets will allow the assessment of fluid exchange between the hydrologic systems of upper and lower plate. The post-doctoral fellow will identify water expulsion along faults in the down- going plate as it migrates upward into the upper plate. The results from this study will contribute to answer the two key questions in the GeoPRISMS Subduction Cycles and Deformation science plan: "How are volatiles, fluids, and melts stored, transferred, and released through the subduction system?" and "How do volatile release and transfer affect the rheology and dynamics of the plate interface, from the incoming plate and trench through to the arc and backarc?"Broader Impacts: The proposed work will provide a better understanding of the geohazard potential in subduction zones, which is particularly relevant for the Pacific Northwest region where large magnitude earthquakes have occurred on the Cascadia megathrust in recent history. The project will support the postdoctoral training of an early-career female scientist. The results of the study will be presented at workshops and conferences and will contribute to the high school curriculum development program at UTIG.