Preliminary Results from Paleoseismic Excavations across the San Andreas Fault at the Scarp Creek Site on the San Francisco Peninsula, California
Abstract
The timing of large earthquakes prior to 1906 on the Peninsula section of the San Andreas Fault (SAFP) is poorly understood. However, four paleoseismic excavations across the SAFP at the Scarp Creek site on the Filoli estate, near Woodside, California, provide age constraints for several pre-historic, Holocene surface ruptures. Sediments exposed in the trenches include fluvial, paludal, and colluvial strata, most of which contain abundant material for radiocarbon analysis. Radiocarbon samples collected from the exposed sediments yield ages that range from modern to approximately 2000 years. Within the approximately 15-m-wide fault zone, we recognize several faults associated with the most recent earthquake (MRE), which occurred in 1906. These faults rupture a buried soil that is overlain by approximately one meter of unfaulted, post-MRE sediments. Most samples collected from these unfaulted sediments yield calibrated, two-sigma, radiocarbon age ranges that extend into the 20th century, consistent with our interpretation that this event horizon represents the 1906 earthquake. We interpret an earlier earthquake based on upward fault terminations deeper in the stratigraphic section. Our preliminary analysis of radiocarbon samples collected from above and below the event horizon suggests that the age of this event is constrained to CE 1280-1390, using our calibrated, two-sigma radiocarbon age ranges. A previous earthquake, is constrained by our preliminary analysis to CE 1020-1160, also using our calibrated 2-sigma radiocarbon age ranges. We interpret at least two earlier earthquakes in this stratigraphic section and anticipate that additional radiocarbon analyses will provide age constraints for these earlier earthquakes.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.T41B2922P
- Keywords:
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- 8107 Continental neotectonics;
- TECTONOPHYSICSDE: 8118 Dynamics and mechanics of faulting;
- TECTONOPHYSICSDE: 8123 Dynamics: seismotectonics;
- TECTONOPHYSICSDE: 8175 Tectonics and landscape evolution;
- TECTONOPHYSICS