HR: 17:30h
AN: NS24A-07    [Abstracts]
TI: High-Resolution Seismic Imaging of Active Strike-Slip Faults in Coastal and Offshore Southern California
AU: Barth, M
EM: mike@subsea-usa.com
AF: Subsea Systems, Inc., P.O. Box 5586, Oxnard, CA 93031-5586, United States
AU: * Legg, M R
EM: mrlegg@attglobal.net
AF: Legg Geophysical, 16541 Gothard Street, Suite 107, Huntington Beach, CA 92647, United States
AB: Identifying and locating active faults in coastal and offshore areas require high-resolution geophysical methods due to the subaqueous environment. Multi-channel seismic reflection profiling using high-frequency (100-10,000 Hz) energy sources and state-of-the-art digital streamers provide excellent high-resolution images of subsurface structure in layered coastal and offshore sediments. Other geophysical methods, such as electrical resistivity, and geotechnical methods, such as cone penetrometer methods, supplement the seismic profiles to map fault traces onto adjacent subaerial sites. In some cases, transition zone seismic methods can be used where subaqueous energy sources are recorded both by hydrophones in the water and geophones on the adjacent subaerial sites, or vice versa with land-based seismic sources. For seismic hazard evaluations, the geophysical studies must be combined with geologic ground truth typically obtained from boreholes. Coastal geology, where land meets sea and changing sea levels shift sediment depositional environments from subaerial to subaqueous produce complex imaging challenges. Careful data acquisition and processing must be used to match acoustic source/receiver combinations with anticipated subsurface geologic structure and to achieve imaging requirements. Shallow gas and other buried geologic anomalies sometimes disrupt the subsurface image, which complicates the geologic interpretation. We present several examples of high- resolution seismic profiles used to identify and locate active (Holocene) fault traces in coastal and offshore areas of southern California necessary for earthquake fault rupture evaluations (Alquist-Priolo Earthquake Fault Zones).
DE: 0935 Seismic methods (3025, 7294)
DE: 7294 Seismic instruments and networks (0935, 3025)
DE: 8010 Fractures and faults
DE: 8015 Local crustal structure
DE: 8107 Continental neotectonics (8002)
SC: Near-Surface Geophysics [NS]
MN: 2007 Fall Meeting