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Poster #062, Earthquake Geology

At least twelve event Holocene to late Pleistocene paleo-earthquake record on the central Garlock fault at Koehn Lake, southern California

Dannielle M. Fougere, James F. Dolan, Chris Anthonissen, Judith Gauriau, Andrew H. Ivester, Sally F. McGill, & Ed J. Rhodes
Poster Image: 

Poster Presentation

2021 SCEC Annual Meeting, Poster #062, SCEC Contribution #11325 VIEW PDF
To improve the paleo-earthquake record of the Garlock fault, a major sinistral strike-slip fault that extends approximately E-W across the Mojave Desert in southeastern California, we revisited a paleo-seismic site at Koehn Lake on the west-central section of the fault. This site was recognized in previous trenching studies by Burke (1979) and Madden & Dawson (2006) as having excellent playa-margin/distal alluvial fan stratigraphy and numerous well-defined structural event markers. We excavated a 37-m-long, 2.5-m-deep trench across the Garlock fault at this site ~20 m east of the previous trenches. This trench revealed evidence for at least twelve surface rupturing events during Holocene... and the latest Pleistocene time, extending back into the terminal pluvial Koehn Lake deposition. In order to constrain individual event ages, we will employ the newly developed post-IR infrared stimulated luminescence (p-IR IRSL) protocol, together with radiocarbon dating. We collected 71 p-IR IRSL and 194 radiocarbon samples from throughout the trench, of which 48 radiocarbon samples have already been dated. Using these two geochronometers will allow for numerous 1:1 comparisons of ages. These results yield the longest current record of paleoearthquakes on the Garlock fault, providing insight into the fault's long-term behavior. Specifically, these well-constrained ages of individual paleo-surface ruptures at Koehn Lake extend the paleo-earthquake record at the nearby El Paso Peaks (EPP) site (Dawson et al., 2003) on this section of the Garlock fault back into the earliest Holocene, and possibly latest Pleistocene time. This record will allow us to determine whether the pronounced temporal clustering of earthquakes observed at the EPP site has been a repeated feature of displacement along the fault. Moreover, our detailed paleo-earthquake record will facilitate comparisons with records at other nearby sites along the central and western segments of the Garlock fault, providing constraints on the lateral extents of previous ruptures. In turn, these results, together with comparisons of paleo-earthquake records from the eastern California shear zone and the San Andreas faults will shed light on potential fault interactions in southern California.