Cruise report for O1-99-SC Southern California Earthquake Hazards project

The focus of the Southern California Earthquake Hazards project is to identify the landslide and earthquake hazards and related ground-deformation processes occurring in the offshore areas that have significant potential to impact the inhabitants of the Southern California coastal region. The project activity is supported through the Coastal and Marine Geology Program of the Geologic Division of the U. S. Geological Survey (USGS) and is a component of the Geologic Division's Science Strategy under Goal 1—Conduct Geologic Hazard Assessments for Mitigation Planning (Bohlen et al., 1998).

The project research is specifically stated under Activity 1.1.2 of the Science Strategy: Earthquake Hazard Assessments and Loss Reduction Products in Urban Regions. This activity involves "research, seismic and geodetic monitoring, field studies, geologic mapping, and analyses needed to provide seismic hazard assessments of major urban centers in earthquake-prone regions including adjoining coastal and offshore areas." The southern California urban areas, which form the most populated urban corridor along the U.S. Pacific margin, are among a few specifically designated for special emphasis under the Division's science strategy (Bohlen et al., 1998). The primary objective of the project is to help mitigate the earthquake hazards for the Southern California region by improving our understanding of how deformation is distributed (spatially and temporally) in the offshore with respect to the onshore region. To meet this objective, we are conducting field investigations to observe the distribution, character, and relative intensity of active (i.e., primarily Holocene) deformation within the basins and along the shelf adjacent to the most highly populated areas (Fig. 1). In addition, acoustic imaging should help determine the subsurface dimensions of the faults and identify the size and frequency of submarine landslides, both of which are necessary for evaluating the potential for generating destructive tsunamis in the southern California offshore. In order to evaluate the strain associated with the offshore structures, the initial results from the field mapping under this project will be used to identify possible sites for deployment of acoustic geodetic instruments to monitor strain in the offshore region. A major goal of mapping under this project is to provide detailed geologic and geophysical information in GIS data bases that build on the earlier studies and use the new data to precisely locate active faults and to map recent submarine landslide deposits.