Evaluation of Use of Remote-sensing Imagery in Refinement of Geologic Mapping for Seismic Hazard Zoning in Northern Los Angeles County, California

The California Seismic Hazards Mapping Act of 1990 directs the California Geological Survey (CGS) to delineate seismic hazard zones of required investigation for earthquake-induced ground failures specifically, liquefaction and seismically triggered landslides. To date, more than 100 official Seismic Hazard Zone maps have been released, covering 200 cities and unincorporated areas in ten counties in California. We use both remote sensing and GIS data layers in the production of the Seismic Hazard Zone maps. One of the most important primary data layers is geology. The quality and accuracy of existing geologic maps vary, however, because of differences in purpose of mapping, scale or levels of detail, presence or absence of standard nomenclature, and types of map projection/registration. To address this problem, the CGS Seismic Hazard Mapping Program (SHMP) conducted a study in the sparsely to highly vegetated terrain of northern Los Angeles County to determine if remote-sensing imagery could improve or enhance the geologic information being used in seismic hazard zoning. We evaluated imagery that included ASTER, Landsat 7 ETM, SPOT, USGS DEM and DOQQ, and airborne Interferometric SAR (IFSAR). All imagery was processed and/or observed on ENVI, ILWIS, Intergraph MGE, GeoMedia, and MapInfo. The evaluation was based on application of different algorithms to accomplish various geologic “tasks” such as: 1) discrimination of geologic contacts between bedrock and unconsolidated Quaternary deposits, 2) recognition and delineation of landslides, 3) confirmation of previously mapped geologic contacts, and 4) verification of cartographic registration of digital geologic maps. We found that applicability and utility of single remote-sensing images for these tasks varied considerably, but the use of combinations of multiple images from different sensors significantly increased the utility of the imagery for our mapping/zoning process. The overall results of the evaluation are presented in tables that rate the various sensors and algorithms.