USGS - science for a changing world

Open-File Report 2008-1246

High-Resolution Chirp and Mini-Sparker Seismic-Reflection Data From the Southern California Continental Shelf—Gaviota to Mugu Canyon


In September, 2007, and June-July, 2008, the U.S. Geological Survey (USGS) collected shallow seismic-reflection data from the continental shelf offshore of southern California between Gaviota and Mugu Canyon, in support of the California Coast State Waters Mapping Project operated by the California Coastal Conservancy ( These new, high-resolution data allow characterization of the continental shelf and shallow slope, where sediment derived from steep coastal mountain ranges accumulates along a tectonically active continental margin affected by activity of the San Andreas Fault system.

The study area is of particular interest for a plethora of geologic and ecologic considerations. Understanding patterns of sediment dispersal and deposition from small, steep, mountainous watersheds is particularly important in regional and global sedimentological investigations because drainage basins of this type collectively contribute more sediment to the oceans than do larger watersheds (Milliman and Syvitski, 1992). Imaging sediment deposits and topography (including submarine canyons) on the southern California shelf is necessary for developing marine and nearshore sediment budgets and for understanding and predicting the likely transport pathways of sediment-bound pollutants. Sedimentary deposits in this area have also, in previous studies, yielded paleoclimate records from Tertiary and Quaternary time that are among the highest resolution in the world (Behl and Kennett, 1996; Nicholson, 2006). In addition, the interaction of sediment on this shelf and in the Santa Barbara Basin with active faults has generated large landslide features (Fisher, 2005), indicating substantial geohazard potential in this area.

High-resolution (meter-scale) imagery from the uppermost shelf sediment facilitates mapping of recent sediment deposits, information that is used by local and State agencies to assess the feasibility of sediment retention, excavation, and beach-nourishment projects. Images of the Ventura and Santa Clara River deltas collected during this work are expected to provide valuable information relevant to potential redistribution of sediment following a planned dam removal in the Ventura River watershed ( Deeper-penetrating seismic reflection images (tens to hundreds of meters) will allow more accurate mapping of fault subsurface geometry and surface expression for use in geohazard assessment. Features associated with hydrocarbon resources were also imaged, including multiple natural gas seeps.

Data collected during this study provide geologic information that is essential to natural-resource management at State and local levels, as well as to future research on the sedimentary, tectonic, and climatic record of southern California.

For more information contact: Ray Sliter

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