HR: 08:15h
AN: OS31A-02    [PDF]
TI: Ages of Potentially Tsunamigenic Landslides in Southern California
AU: * Lee, H J
EM: hjlee@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 United States
AU: Normark, W R
EM: wnormark@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 United States
AU: Fisher, M A
EM: mfisher@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 United States
AU: Greene, H G
EM: greene@mlml.calstate.edu
AF: Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, CA 95039 United States
AU: Edwards, B D
EM: bedwards@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 United States
AU: Locat, J
EM: jlocat@ggl.ulaval.ca
AF: Laval University, Medicene Street, Quebec, Que G1K 7P4 Canada
AB: The innermost basin slopes of the Southern California Borderland contain numerous large-scale submarine landslides. Many of these are of sufficient size to have generated tsunamis when they occurred, assuming that the imaged deposits represent a single failure and that their motion was rapid. We have obtained high resolution subbottom profiles of five well-defined slope failures. These failures are located off the Palos Verdes Peninsula, within Santa Monica Bay, and within the Santa Barbara Channel. A landslide motion and tsunami generation model for one of the landslides shows that it likely generated a tsunami with a source height of at least 8 m. For four of the failures, ages were determined by identifying acoustic reflectors in the vicinity of the failed masses that either clearly postdate or predate the landslide events. The ages of the reflectors are determined by using seismic-reflection profiles to correlate with dated sections at ODP sites or by directly dating the slide masses with piston cores. In the case of the most recent failure in the Santa Barbara Channel, post-failure sediment deposited on the scar of the landslide was sampled completely with a gravity corer, and the age was estimated based on a representative sedimentation rate. Our assessment shows that three of the four older landslides are approximately 10,000 years old and that the Palos Verdes event was about 7,500 years ago. However, the most recent failure may be as young as 200 years. Such a landslide might have generated a tsunami such as was observed by early Spanish settlers during the 1812 earthquake.
DE: 3022 Marine sediments--processes and transport
DE: 3045 Seafloor morphology and bottom photography
DE: 4564 Tsunamis and storm surges
DE: 5754 Physical properties of materials
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting