Evidence for a High Slip Rate of the Calico Fault in the Eastern California Shear Zone

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Poster Session

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Fault slip rates provide important constraint on seismic hazard assessments. Geologic and geodetic estimates of slip rates across the Eastern California Shear Zone (ECSZ) reveal a discrepancy between the two data sets. Most studies attempting to reconcile the discrepancy have focused on off-fault deformation and the technique limitation of short-term geodetic measurements, while there is less concern about the relatively small number of cited geologic slip rates. The Calico fault is central fault in the Mojave Desert portion of the ECSZ, where published geologic slip rates are between 1 and 2 mm/yr. We determine new geologic slip rates of the Calico fault by dating two offset alluvial fans near the town of Newberry Springs, California. Correlation of the offset fans was based on geomorphic and soil development characteristics. Offset magnitudes are based on high-resolution topography and orthoimagery, and by cropping and matching the alluvial fans along the fault trace. Surface displacements of the two offset fans are ~80 m and ~1120 m. Surface exposure ages of alluvial fan samples are dated using the production of 10Be terrestrial cosmogenic nuclide (TCN). The fan with an ~80 m offset produced an age of ~40 ka, yielding a slip rate of ~2 mm/yr, consistent with previous studies. The fan with displacement of ~1120 m produced an age of ~290 ka, yielding a slip rate of ~4 mm/yr, indicating that the Calico fault likely had a much higher slip rate early and has decreased more recently.

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Citation / Publisher Attribution

Presented at AGU Fall Meeting on December 14, 2016 in San Francisco, CA