Dating of Offset Geomorphic Features Along the Garlock Fault, Mojave Desert, California: Testing a Proposed Earthquake Supercycle Model

James E. Burns, Sally F. McGill, Ed J. Rhodes, James F. Dolan, & Nathan D. Brown

Submitted August 15, 2018, SCEC Contribution #8724, 2018 SCEC Annual Meeting Poster #234

Recent investigations into 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. These previously published investigations suggest a rapid slip rate 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. This period of relative quiescence, followed by a period of more frequent large earthquakes suggests the possibly of an earthquake “Super-cycle”. 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. We are in the process of using post-IR50-IRSL225 to date a number of 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. The ages of these offset features will be compared to the published ages of prehistoric earthquakes from paleoseismic trenches at El Paso Peaks, Christmas Canyon and Echo Playa to determine the amount of slip in each of these past events. In the El Paso Mountains, we have sampled a 14-m offset channel and an 18-m offset alluvial fan, for which IRSL ages are pending. The 14-m offset is interpreted to represent the slip in the past two earthquakes combined, and the 18-m offset is interpreted to represent the slip in the past three earthquakes combined. We also intend to sample a 7-m offset channel, which is inferred to represent the slip in the most recent earthquake. Comparison of the ages of these features with published dates from the El Paso Peaks trench will either confirm or modify the number of earthquakes we have tentatively inferred for each offset feature. In Pilot Knob Valley, we intend to sample geomorphic features offset ~ 3 m, ~5-6 m, ~ 8 m, ~12 m and ~15 m. These ages will be compared to dates of prehistoric earthquakes in paleoseismic trenches at Echo Playa and Christmas Canyon in order to estimate the amount of slip in each of past ~5 earthquakes. These results will constrain the late Holocene slip history for the Garlock fault at El Paso Mountains and Pilot Knob Valley, allowing us to examine changes in slip rate and recurrence interval over time and along strike.

Key Words
Garlock, incremental slip-rate, slip per earthquake, IRSL

Citation
Burns, J. E., McGill, S. F., Rhodes, E. J., Dolan, J. F., & Brown, N. D. (2018, 08). Dating of Offset Geomorphic Features Along the Garlock Fault, Mojave Desert, California: Testing a Proposed Earthquake Supercycle Model. Poster Presentation at 2018 SCEC Annual Meeting.


Related Projects & Working Groups
Earthquake Geology