DATING OF OFFSET GEOMORPHIC FEATURES ALONG THE GARLOCK FAULT, MOJAVE DESERT, CALIFORNIA: TESTING A PROPOSED EARTHQUAKE SUPERCYCLE MODEL

Recent investigations of the Garlock Fault at the northern edge of the Mojave Desert point to a strongly irregular pattern of earthquake recurrence, which may be related to temporal variations in slip rate on the fault. Previously published investigations suggest a rapid slip rate (Dolan et al., 2016) coinciding with a succession of four closely spaced earthquakes within the past 2 ka, preceded by a 3000-year lull with no earthquakes evident in a paleoseismic trench near El Paso Peaks (Dawson et al., 2003). This period of relative quiescence, followed by a period of more frequent large earthquakes, suggests the possibility of an earthquake “Super-cycle” (Dolan et al., 2016). To further investigate variations in slip rate and the possibility of an earthquake “super-cycle” on the Garlock fault, we are constructing a detailed slip history of the Garlock fault utilizing drone surveys, LiDAR data, structure from motion datasets, and post-IR₅₀-IRSL₂₂₅ luminescence dating to measure and date several geomorphic features that have been offset in the past 1-5 earthquakes on the Garlock fault in the El Paso Mountains and Pilot Knob Valley areas. In the El Paso Mountains, initial results indicate that the preferred age for a channel left-laterally offset by 13.8 (+1.8, -3.2) m is between 1040-1450 BP and that the age of an alluvial fan left-laterally offset 24 (+4, -3) m is 2450-3690 BP. A comparison of these ages with published ages of prehistoric earthquakes from the El Paso Peaks trench suggests that the ~14-m offset occurred during the two most-recent earthquakes, whereas the ~24-m offset likely accumulated during the past four earthquakes. In Pilot Knob Valley, we have sampled geomorphic features such as terrace risers and alluvial fans offset by ~ 4 m, ~6.1 m, ~ 8.2 m, and ~15 m. Comparison of these pending ages with the dates of prehistoric earthquakes in paleoseismic trenches at Echo Playa and Christmas Canyon, California will enable estimation of the amount of slip in the past several earthquakes along that stretch of the fault. The results will constrain the late Holocene slip history for the Garlock fault at El Paso Mountains and Pilot Knob Valley allowing for the examination of changes in slip rate and recurrence interval over time and along strike.