Distributed fault slip in the eastern California shear zone: Adding pieces to the puzzle near Barstow, California

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Abstract

We investigate the dextral Lockhart and Mt. General faults, which are among four active structures in the northwestern portion of the eastern California shear zone (ECSZ). Early mapping depicts the Lockhart and Mt. General faults as discontinuous fault traces that continue northwest of the Lenwood Fault. Recent work indicates that the Lenwood Fault slips at ~0.2-1.0 mm/yr over the past ~8 ka and 0.8 ± 0.2 mm/yr since ~37 ± 7 ka. We reconstruct the record of fault slip for the Lockhart and Mt. General faults using high-resolution Structure-from-Motion built topography, field observations, geochronology, and gravity data. Geomorphic offsets along a Holocene-active trace of the Lockhart Fault indicate dextral displacement between ~4 and 6 m. A feldspar infrared stimulated luminescence (IRSL) age implies surface abandonment and at least one earthquake after 3540 ± 880 ka (2σ). The implied Holocene fault slip rate on the Lockhart Fault is between ~0.9 and 2.3 mm/yr. Holocene-active traces of the 19-km-long Mt. General Fault are marked by southwest-facing scarps and dextral offsets of ~4–5 m on alluvial fans, with down-to-the-southwest vertical offset of ~0.3 m. Summing dextral displacements across subparallel fault strands yields a maximum of ~7–8 m. A feldspar IRSL age indicates deposition of the alluvial fans since 11,380 ± 1700 ka (2σ). This results in a Holocene slip ~0.3–0.6 mm/yr, possibly ranging up to 1.0 mm/yr. Taken together, these observations imply a net Holocene dextral slip rate for active faults in Hinkley Valley at 1.2–3.3 mm/yr―higher than expected given published fault slip rates along-strike to the southeast.

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Publication type Conference Paper
Publication Subtype Conference Paper
Title Distributed fault slip in the eastern California shear zone: Adding pieces to the puzzle near Barstow, California
Year Published 2019
Language English
Publisher Desert Symposium
Contributing office(s) Crustal Geophysics and Geochemistry Science Center, Geology, Minerals, Energy, and Geophysics Science Center
Description 7 p.
Larger Work Type Book
Larger Work Subtype Conference publication
Larger Work Title Exploring the ends of eras in the eastern Mojave Desert: 2019 Desert symposium field guide and proceedings
First page 134
Last page 140
Conference Title 2019 Desert Symposium
Conference Location Zzyzx, CA
Conference Date Apr 2019
Country United States
State California
City Barstow
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