Investigating Outer-Rise Normal Dip-Slip Fault Parameters and Their Tsunamigenic Properties Along the Puerto Rico Trench
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Nielson, Quincey
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Abstract
Outer-rise normal faults may present a significant and underappreciated tsunami risk due to their relatively steep faulting angles and potentially large fault slips. Such is the example along the Puerto Rico Trench, where bathymetry reveals large normal faults outward of the trench whose risk to nearby populations is not yet quantified. We created a set of tools to semi-automatically determine basic fault properties from topographic relief, allowing us to quantify the seismogenic and tsunamigenic potential in the region. Using high resolution bathymetric data in the region, we visually inspect a gradient field for suspected faults, selecting points defining the footwall alongside a fault. Orthogonal downdip transects are then extracted to jointly evaluate the elevation, gradients, and curvature along profiles to determine the likely uneroded and eroded fault scarp dips and offsets. From a distribution of results along each fault, we are then able to calculate statistically robust results. For long and sometimes complex faults, transects were initially determined from sub-faults but later recombined. We used this process to compile 148 sets of transects for a total of 97 faults. With this cataloged dataset of outer-rise faults, we incorporated convergence rates to determine the total slip rate across these faults, putting an upper-bound on the earthquake and tsunami potential of these faults. Individual faults of interest were further analyzed and to generate estimates for event magnitude and maximum run-up. Given the generalizable nature of this tool, it can be easily applied to outer-rise features at other subduction zone environments.
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