GPR Investigation of Fault-Deformed Historic and Late Holocene Paleo-Shorelines of Owens Lake, CA: a Course-Based Research Experience

This course-based undergraduate and graduate research experience sought to image deformation along the Owens Valley Fault Zone at the northwest corner of Owens (dry) Lake, California. Seismic deformation in unconsolidated sediments can form slip surfaces and deformation bands, which can give paleo-seismic insight, but may be difficult to image using near-surface geophysics. Owens Lake, located along the Owens Valley Fault Zone, in the Eastern portion of California, contains Quaternary regressive beach ridges that deformed during a large earthquake in 1872 and other previous events. To investigate the possible paleoseismic record preserved by those beach ridges and underlying lake beds, we combined aerial photos and LiDAR into a GIS and collected eight ground penetrating radar (GPR) profiles in the zone of co-seismic deformation. LiDAR data from the flight of beach ridges revealed precise vertical deformation magnitude and sense. GPR profiles collected along and across the beach ridges displayed various sedimentological features but also warped bedding, with only a few offset reflectors where the profiles cross the deformed topography. This pattern of reflectors differs from the horizontal pattern observed outside the deformation zone. The topographic and reflector warping was broadly distributed and the offsets were subtle. Slip within this small study area is more likely distributed in many cryptic deformation bands and slip surfaces rather than on one or a few fault ruptures.