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Preliminary results of marine paleo-seismology from MCS, CHIRP, and coring off Catalina Island,

Ethan F. Williams, Christopher M. Castillo, Simon L. Klemperer, Kate Maher, Robert D. Francis, & Mark R. Legg

Published 2015, SCEC Contribution #6095

Submerged paleo-shorelines around Catalina Island record information
about the paleo-seismicity and evolving morphology of the Channel
Islands, and provide constraints on Quaternary sea-level history of
Southern California. We acquired high-resolution uniboom seismic data in
2014 across these paleo-shorelines and intervening marine terraces, with
a particular focus on the Long Point Fault, a strike-slip fault subparallel to
the San Andreas system. Each terrace corresponds to a low-stand in the
Quaternary sea-level curve and can be used as paleo-horizontal datum for
constraining the ages of Quaternary tsunamogenic landslides and major
vertical offset on the Long Point Fault. Determining the age of the terraces
is essential to understanding the slip history of the Long Point Fault and the potential for future tsunamogenic landslides. Radiometric dates are necessary to refine our sequence-stratigraphic interpretation and constrain terrace-cutting events. Our SCEC-funded coring cruise off Catalina Island was conducted in June 2015 to retrieve dateable material from subsided terraces. We used high-resolution MCS and CHIRP data to locate outcrops of terrace deposits, which we then sampled using a gravity core and grab sampler while simultaneously running CHIRP to ensure that we successfully hit our target. Samples include carbonate-rich sands from depths of 32-350 m bsl, and wave-rounded cobbles >8.75 km offshore at depths of >250 m bsl. At the time of writing, corals and mollusks recovered from the cores are undergoing U-series dating at the Stanford University ICP-MS/TIMS
Facility and 418O measurements at the Stanford University Stable Isotope Biogeochemistry Lab. Further samples have been sent to Lawrence Livermore National Labs for radiocarbon dating through their SCEC partnership.
Preliminary results from our SCEC cruise were used to motivate and guide two successful ROV dives off Catalina Island by the E/V Nautilus in August 2015. The dives yielded samples from outcrops of terrace deposits as well as high-definition video of these submarine features, and the fault-scarp of the Santa Cruz-Catalina strike-slip fault. Wave-rounded cobbles and intertidal fauna in deposits surrounding the island confirm the hypothesis that Catalina has experienced at least 250m of subsidence since its uplift during the Pliocene.

Williams, E. F., Castillo, C. M., Klemperer, S. L., Maher, K., Francis, R. D., & Legg, M. R. (2015). Preliminary results of marine paleo-seismology from MCS, CHIRP, and coring off Catalina Island,. Poster Presentation at 2015 SCEC Annual Meeting.