Resolution of Site Response Issues from the Northridge Earthquake

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9529159 Aki This project brings together a strongly coordinated group of geologists, geotechnical engineers and seismologists from a number of organizations to address geotechnical site characterization and ground motion response issues resulting from the Northridge earthquake. The proposed work is heavily leveraged by cost-sharing from the California Department of Transportation, with additional cost-sharing from the Electric Power Research Institute, the Southern California Earthquake Center, and the U.S. Geological Survey, and with cooperation from the California Department of Mines and Geology. The objectives of the project are: 1) collection, compilation, and rapid dissemination of high- quality site geotechnical and geophysical data to the research community; and 2) focused analyses limited to the following: * determining the extent to which local site and regional wave propagation effects control strong ground motion, including nonlinear site response; * evaluating the adequacy of the conventional approach to estimating site effects using: measured shear-wave velocities, the results of laboratory tests, and one-dimensional equivalent- linear and nonlinear analyses; * assessing the degree of model complexity (2- and 3-D analyses) required to adequately explain site effects; and * determining the uncertainties in measured properties and how these uncertainties affect ground motion predictions. The research objectives are addressed in three phases by the integrated group of geologists, seismologists and geotechnical engineers. Extensive coordination between institutions is facilitated through a formal advisory structure. In Phase 1, a series of geotechnical investigations are conducted at significant sites of strong motion recordings and/or structural failures. In Phase 2, data collected in Phase 1 is evaluated and combined with results of other data collection efforts to establish a comprehensive database for modeling ground motion. The aim is to establish standard 1-D geotechnical models that include material strain dependencies, as well as 2- and 3-D structural models. A workshop will facilitate coordination between investigators and dissemination of data. Phase 3 involves site response analyses of the data collected in Phase 2, with comparisons made of ground motion response calculations to Northridge earthquake observations. The final report will document site investigations and site response issues as well as all of the ground motion analyses conducted. ***