HR: 0800h
AN: S11A-0159    [Abstracts]
TI: Reducing Seismic Hazards Through Local Geologic Review, San Luis Obispo County, California
AU: * Rosenberg, L I
EM: lrosenberg@co.slo.ca.us
AF: San Luis Obispo County Planning Dept., County Government Center, Room 310, San Luis Obispo, CA 93408 United States
AB: San Luis Obispo County is located on the California coastline midway between the large metropolitan areas of Los Angeles and San Francisco. Until the early 1990s, San Luis Obispo was mainly rural and believed to have a lower seismic hazard compared to Los Angeles and the San Francisco Bay area. Economic growth in the middle 1990s caused the county to grow nearly 30 percent in 5 years, with new residents emigrating from Los Angeles and the San Francisco Bay area. Local government had vague geologic report requirements. Hence, the quality of reports submitted to the County was poor. Two events changed this: first, the County established a new County Geologist position and program; second, the 2003 M6.5 San Simeon earthquake made the general public greatly aware of the seismic risks in their own backyard. Through stringent peer-review, the County Geologist program has reduced seismic losses by requiring detailed engineering geologic reports based on guidelines outlined in the California Geological Survey's Special Publication 117. In addition, in-depth liquefaction studies are required in the community of Oceano, where liquefaction was previously unknown, but revealed in the San Simeon earthquake. Other improvements in seismic hazard characterization include trenching late Quaternary faults, using probabilistic estimates of ground motion, and recognition of enhanced ground shaking in basins and along ridgetops. The success of the County Geologist program was based on several factors: hiring a local geologist with expertise in seismic hazards, support of the County's decision-makers, and cooperative technical studies with the U.S. Geological Survey, the California Geological Survey, CalTrans, and the California Coastal Commission. Some resistance was initially from the land development community, but was resolved by applying policy fairly and uniformly. Thus, standard-of-practice in seismic hazard characterization in San Luis Obispo County is closer to that of the urban parts of state. Local governments should consider creating their own geologic review program, but should be aware of the time and consensus-building involved to create a successful effort. Most importantly, the new program should enact and enforce the most detailed and current guidelines immediately. Subsequent efforts to "raise the bar" become increasing difficult. However, the payoff of increasing public safety and improved knowledge of local seismic hazards make geologic review programs worthwhile.
DE: 7212 Earthquake ground motions and engineering seismology
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 8099 General or miscellaneous
SC: Seismology [S]
MN: Fall Meeting 2005