HR: 0800h
AN: S11A-0163    [Abstracts]
TI: Regional Mapping of Liquefaction Susceptibility in the Central Puget Sound Region, Washington
AU: * Palmer, S P
EM: stephenpalmer@earthlink.net
AF: GeoDesign, Inc, 15575 SW Sequoia Parkway Suite 100, Portland, OR 97224 United States
AU: Perkins, W J
EM: WJP@shanwil.com
AF: Shannon and Wilson, Inc., 400 North 34th Street Suite 100, Seattle, WA 98103 United States
AB: In the late 1980's we began development of a series of regional liquefaction susceptibility maps covering the urban areas of the central Puget Sound region, including the cities of Seattle and Tacoma. In producing these maps we used a standardized approach that utilizes 1:24,000-scale geologic mapping and analyses of geotechnical boring data and allows direct comparison of the liquefaction susceptibility assessments depicted on each map. The geologic units in a study area were grouped based on their geological and engineering characteristics, and a suite of geotechnical borings was compiled for each geologic grouping. A standard engineering analysis was used to calculate factors-of-safety from standard penetration test N-values, sample descriptions, grain-size analyses, and ground-water depths obtained from the compiled geotechnical borings. Liquefaction factors-of-safety were calculated for two magnitude 7.3 earthquake scenarios, one having a 0.15 g peak ground acceleration (PGA), and the other a 0.30 g PGA. The choice of earthquake scenarios is consistent with an intraplate earthquake similar to the 1949 Olympia and 2001 Nisqually events in the Puget Sound region. Using these factor-of-safety calculations we determined the aggregated total thicknesses of liquefiable material for each boring in a geologic grouping, and normalized these data by expressing the aggregated thicknesses as a percentage of the total penetrated thickness. A series of histograms, one for each earthquake scenario, were used to present the distribution of aggregate liquefiable thicknesses and to assign a liquefaction susceptibility to each geologic grouping. We have calibrated our analyses of liquefaction susceptibility using the liquefaction response observed during the Nisqually earthquake. We developed histograms for each geologic grouping using measured PGA's from this event and the geotechnical boring datasets compiled in the production of the previously published liquefaction susceptibility maps. This calibration allows us to make assessments of other potential earthquakes, and was recently used in our evaluation of liquefaction effects for a Seattle fault scenario.
DE: 7212 Earthquake ground motions and engineering seismology
DE: 7299 General or miscellaneous
SC: Seismology [S]
MN: Fall Meeting 2005