Slip-History for the past 3-4 earthquakes on the central Garlock Fault, Mojave Desert, California

James E. Burns, Sally F. McGill, Kerry Cato, James F. Dolan, Ed J. Rhodes, Sourav Saha, Seth Saludez, & Andrew Suarez

Published September 11, 2022, SCEC Contribution #12533, 2022 SCEC Annual Meeting Poster #112

As part of a larger project, we are contributing to the construction of a detailed slip history of the Garlock fault, by dating geomorphic features that have been offset ~3 to ~24 meters, to estimate the amount of slip in the past 1-4 earthquakes on the Garlock fault. We used aerial photography from drone surveys, as well as hand-held Lidar datasets, to create detailed digital elevation models of 3 offset features in the El Paso Mountains (EPM) and 5 offset features in Pilot Knob Valley (PKV). We used post-IR50-IRSL225 luminescence dating to date these offset geomorphic features.
In El Paso Mountains, initial results indicate that an alluvial fan (site EPM-B) with an age of 3210 ± 440 years BP (average of 3 samples), is left-laterally offset 23 (+2, -4) m. Comparison with published ages of earthquakes from the El Paso Peaks paleoseismic trench (Dawson et al., 2003) indicates that this fan has experienced four earthquakes. This implies an average of ~ 5.75 m slip per earthquake. An abandoned channel that is left-laterally offset by 11 ± 3 m at EPM-A and a terrace offset 9.2 (+ 4.3, - 1.0) m at EPM-B have ages that suggest they experienced two (and only two) earthquakes, suggesting that the average slip per event in the two most recent earthquakes is similar to that in the past four earthquakes.
In Pilot Knob Valley, we have dated alluvial fan deposits in the range of ~1.5 to ~2.7 ka at four sites. At each site, the preferred left-lateral offset of these deposits is in the range of ~14-18 meters. At 3 of these sites the offset could be larger, but no more than ~ 25 m. At site PKV-B, these deposits, which have an IRSL age of 2500 ± 250 years BP, can be offset no more than about 15.5 m. Previously published results from a paleoseismic trench at Echo Playa (8.6 - 12.3 km west of our PKV sites) suggest that three earthquakes have occurred in the past 1870 – 1970 years BP, and the fourth event occurred prior to 2870 years BP (Kemp et al., 2016). Thus, the 1.5 -2.7 ka alluvial deposits have likely experienced three earthquakes, with an average of ~5-6 m per event. An unfaulted alluvial terrace at PKV-E has an IRSL age of 460 ± 70 years BP, indicating that the most recent earthquake in PKV occurred more recently than this, consistent with the age of the youngest earthquake in the three paleoseismic trenches located closest to our PKV sites. Our estimates of the slip in this most recent earthquake range from 3.3 m to 6.5 m at sites PKV-B, -C, -D, and -E.

Key Words
Garlock, Paleoseismology, LiDAR, IRSL,

Citation
Burns, J. E., McGill, S. F., Cato, K., Dolan, J. F., Rhodes, E. J., Saha, S., Saludez, S., & Suarez, A. (2022, 09). Slip-History for the past 3-4 earthquakes on the central Garlock Fault, Mojave Desert, California. Poster Presentation at 2022 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology