ANALYZING OREGON FAULT SCARPS WITH LIDAR TO UNDERSTAND ACTIVE CASCADIA DEFORMATION

Scarps cutting late Quaternary geomorphic surfaces throughout the landscape of Oregon provide evidence of ongoing plate boundary deformation. Active faulting likely results from a variety of processes in the Cascadia region including subduction zone strain, vertical-axis block rotation, back-arc and intra-arc extension, and magmatism. High-resolution topographic data offer a way to analyze scarps at a synoptic scale across the region. The state of Oregon has near complete coverage by at least one QL1 (8 points per square meter) airborne lidar survey, and scarps are well-resolved even below areas of dense forest cover. We are analyzing geomorphic detail of mapped scarps to assess relative ages and cumulative offsets of surface-rupturing faulting. We are developing and applying methods to semi-automatically characterize scarp forms and vertical separations to interrogate the densely sampled bare-earth lidar data. This strategy allows efficient and detailed measurement of spatial variations of offset along individual faults and among multiple structures. When combined with regional ages of faulted geomorphic surfaces and deposits, these measurements will provide improved understanding of relative strain rates across this section of the plate boundary zone. Regional analysis of scarp height and displacement-length scaling will contribute to better understanding of the tectonic and magmatic processes that drive surface-rupturing faulting. Investigation of scarp form will measure effects of surface processes that modify scarps between earthquake rupture events across a large climatic gradient. Broad surface-based analysis provides context for detailed site-specific paleoseismic and slip-rate studies to better characterize seismic hazard in the region.