HR: 08:30h
AN: OS31A-03 INVITED     [PDF]
TI: Dating one Slide Event of the Complex Compound Goleta Submarine Landslide, Santa Barbara Basin, California, USA
AU: * Greene, H
EM: greene@mbari.org
AF: Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, Ca 95039 United States
AU: Fisher, M A
EM: mfisher@usgs.gov
AF: US Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 United States
AU: Normark, W
AF: US Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 United States
AU: Maher, N
EM: nmaher@aoageophysics.com
AF: AOA Geophysics Inc., 7532 Sandholdt Road, Moss Landing, CA 95039 United States
AB: Dating of submarine sediment slumps and slides is fraught with problems, especially those taking place during the past several thousand years. However, we need to develop accurate dating techniques so as to improve our ability to assess the periodicity of, and the actual risk from, these events. The large (130 km2) Goleta landslide located off Coal Oil Point near the town of Goleta, California measures 14.6-km long, extends from 90 m to nearly 574 m below sea level, and is 10.5 km wide. The slide is complex, and includes both buried slump blocks and mudflows, with a surface expression of three distinct segments of failures. Each segment is composed of a distinct head scarp, down-dropped head block, and a slide debris lobe. We estimate that at least 1.75 km3 of surface material represents the most recent displaced events of this slide. Dating of the more recent failures of this slide has been speculative and based on modeling and estimated sediment cover on one of the head scars. The most recent event is thought to be the cause of the reported tsunamis of 1812. However, sophisticated dating of the slide has yet to be done. Recent interpretation of newly acquired seismic reflection profiles indicates that the head slump block of the eastern segment of the slide dammed sediment behind it after it came to rest at the base of the head scarp. We calculated that about 64 m of sediment was dammed behind the block, based on a measured two-way travel time through the sediment pond of 0.075 sec. and an assumed velocity of ~1680 m/sec. Using a sedimentation rate of 1.73 m/Ka to 2.5 m/Ka, the range of sedimentation rates determined by other investigators for the mid- to lower shelf areas of the western Santa Barbara Basin, the time required for deposition would be 37-25.6 Ka. Therefore, if the sedimentation rates are correct and that the ponded sediment represent nothing but normal sedimentation devoid of sloughing or debris flows down the slope, the maximum age of when the block came to rest in its present position would be 37-25.6 Ka. However, given the tectonic dynamics of the area and the instability of the slope in this part of the Santa Barbara Basin, the likelihood of deposits derived from mass movement filling the depression behind the slump block is high, thus suggesting a possible younger age for the failure.
DE: 3022 Marine sediments--processes and transport
DE: 3025 Marine seismics (0935)
DE: 4219 Continental shelf processes
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting