The Seafloor off Greater Los Angeles: Visualizing Gigabytes of Data

Abstract

The seafloor off the greater Los Angeles area was mapped with three different high-resolution multibeam echosounders over a period of three field seasons. The mapping was untaken to provide a base map for ongoing marine geological studies in the area. The combined data set covers the entire continental shelf and basin slope from as shallow as the 20-m isobath (in some places the 5-m isobath) on the inner shelf to the 800-m isobath on the basin floor. These data represent more than 5 billion georeferenced depth soundings that cover an area of more than 1000 km2. In addition, each depth sounding location has an associated acoustic backscatter value, thereby effectively doubling the data volume that needs to be visualized. And, when the land area DEM is draped with Landsat imagery, the dataset enlarges to more than 6 billion points. The data can be visualized with many standard GIS packages but statically investigating 2D map views of such a large dataset, one view at a time, is cumbersome and can be tedious. In addition, the bathymetric data have various spatial resolutions that depend on the water depth. A dynamically interactive 3D visualization package that allows georeferenced datasets of mixed spatial resolutions was chosen to enhance the interpretation phase of the dataset. Some of the capabilities of this software will be demonstrated during the presentation. The bathymetric data reveal the complex nature of this basin-margin environment. Large debris avalanches have scarred the basin slope off the Palos Verdes Peninsula. Undercutting along the base of the basin slope suggests current erosion. The morphologies of the submarine canyons in the area range in complexity from a simple single canyon channel, such as Redondo Canyon, to a complex system of canyon channels, such as Newport and San Gabriel Canyons. Distinctive small canyon morphologies suggests the possibility of fresh-water springs outcropping along the San Pedro upper basin slope and along the mid and lower basin slope. Large sections of the southern portion of the margin appear to be slowly creeping downslope. The continental shelves in the area vary from sediment covered with fields of bedforms to areas of rock outcrops. Linear trends of outcrops on the San Pedro shelf suggest previously unmapped structural trends. Very little of the floors of Santa Monica and San Pedro Basins have been mapped. However, the areas that have been mapped show a succession of channel downcuts that suggest tectonic uplift of San Pedro Basin as well as debris deposits and channel meanders.

Department

Center for Coastal and Ocean Mapping

Publication Date

12-2002

Volume

83, Issue 47

Journal Title

EOS Transactions, American Geophysical Union

Conference Date

Dec 6 - Dec 10, 2002

Publisher Place

San Francisco, California, USA

Publisher

American Geophysical Union Publications

Document Type

Conference Proceeding

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