Investigation of late Pleistocene and Holocene activity in the San Gregorio fault zone on the continental slope north of Monterey Canyon, offshore central California

Bulletin of the Seismological Society of America
By: , and 

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Abstract

We provide an extensive high‐resolution geophysical, sediment core, and radiocarbon dataset to address late Pleistocene and Holocene fault activity of the San Gregorio fault zone (SGFZ), offshore central California. The SGFZ occurs primarily offshore in the San Andreas fault system and has been accommodating dextral strike‐slip motion between the Pacific and North American plates since the mid‐Miocene. Our study focuses on the SGFZ where it has been mapped through the continental slope north of Monterey Canyon. From 2009 to 2015, the Monterey Bay Aquarium Research Institute collected high‐resolution multibeam bathymetry and chirp sub‐bottom profiles using an autonomous underwater vehicle (AUV). Targeted samples were collected using a remotely operated vehicle (ROV) to provide radiocarbon age constraints. We integrate the high‐resolution geophysical data with radiocarbon dates to reveal Pleistocene seismic horizons vertically offset less than 5 m on nearly vertical faults. These faults are buried by continuous reflections deposited after ∼17.5  ka and likely following erosion during the last sea‐level lowstand ∼21  ka, bracketing the age of faulting to ∼32–21  ka. Clearly faulted horizons are only detected in a small area where mass wasting exhumed older strata to within ∼25  m of the seafloor. The lack of clearly faulted Holocene deposits and possible highly distributed faulting in the study area are consistent with previous interpretations that late Pleistocene and Holocene activity along the SGFZ may decrease to the south. This study illustrates the complexity of the SGFZ, offshore central California, and demonstrates the utility of very high‐resolution data from combined AUV (geophysical)–ROV (seabed sampling) surveys in offshore studies of fault activity.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Investigation of late Pleistocene and Holocene activity in the San Gregorio fault zone on the continental slope north of Monterey Canyon, offshore central California
Series title Bulletin of the Seismological Society of America
DOI 10.1785/0120160261
Volume 107
Issue 3
Year Published 2017
Language English
Publisher Seismological Society of America
Contributing office(s) Pacific Coastal and Marine Science Center
Description 13 p.
First page 1094
Last page 1106