EARTHQUAKE-INDUCED LANDSLIDE SUSCEPTIBILITY OF HILLSLOPES ALONG THE LOWER KERN RIVER, CA BASED ON HISTORICAL FAULT RUPTURE SCENARIOS

The lower Kern River in the southern Sierra Nevada has deeply incised a narrow gorge into Late-Cretaceous plutonic bedrock. The steep outcrop studded hillslopes that flank the lower Kern River are typically mantled by large detached boulders intermingled with finer colluvial and alluvial deposits. The main travel corridor linking the city of Bakersfield to the communities of Lake Isabella and Kernville, CA SR-178, parallels this section of the lower Kern River and is frequently closed due to landslides triggered by precipitation. This region is also in close proximity to several major, seismically active faults that include faults within the San Andreas, Garlock, and Owens Valley fault systems. Historically significant earthquakes in the region include the 1857 Fort Tejon Earthquake (M7.9), the 1872 Owen’s Valley Earthquake (M7.4-7.8), and the 1952 Kern County Earthquake (M7.3). The 2019 Ridgecrest Earthquake Sequence that began on July 4, 2019, with a M6.4 foreshock followed by the mainshock on July 5, 2019 (M7.1) triggered a rockfall that blocked traffic on the SR-178 at the mouth of the Kern River Canyon approximately 127 km (80 mi) away from the epicenter. This region was shown to have a <0.2% probability of landslides in initial estimates of Ground Failure produced by the United States Geological Survey (USGS). In this study, we will investigate the susceptibility of hillslopes, along the lower Kern River, to earthquake-induced landslides using historical earthquake scenarios. We will also compare results obtained by using the USGS preferred ground failure model (Nowicki-Jessee et al., 2018), a recommended alternative model (Godt et al., 2008), and a physical model using detailed local datasets, to help us examine why the rockfall at the mouth of the Kern River had such a low probability of occurrence.