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Marine Crustal Reflection Profiling Offshore Santa Maria Basin Westward to Base of Continental Slope

Anne S. Meltzer, Alan R. Levander

In November 1986, Rice University and HARC conducted a 425-km regional seismic reflection survey. We acquired 16 sec of data using a 180 channel system with 25-m group spacing and 4.7 km maximum offset. The source was a 6,000 in.3 2,000-psi air gun array fired every 50 m. Two of the reflection profiles, a 100-km dip profile and an 88-km strike line, have been processed and interpreted at Rice University. The dip profile crosses the northern Santa Maria basin, and the Santa Lucia high off California, then extends into the deep ocean basin. The strike profile, shot down the basin axis approximately 30 km west of the coastline, extends from the northern Santa Maria basin south as far as Point Sal. Interpretation of the dip profile shows that the Santa Lucia high i underlain at 6 sec two-way traveltime by a strong coherent reflector that can be traced for more than 50 km from the deep ocean basin to just west of the Santa Lucia Bank fault. Conversion to depth places this reflector at 11-14 km, with a dip of 6.5° toward the coast. We interpret this reflector to represent the top of subducted oceanic crust of the Pacific plate. More than 12 km of material has been accreted above this reflector. A deep reflection at 8 sec beneath the Santa Lucia high may be from the Moho. The strike profile crosses a major fault that separates the uplifted northern Santa Maria basin from the deeper southern part of the basin. Several reflection events are visible beneath acoustic basement between 2 and 8 sec two-way traveltime.

AAPG Search and Discovery Article #91035©1988 AAPG-SEPM-SEG Pacific Sections and SPWLA Annual Convention, Santa Barbara, California, 17-19 April 1988.