Seismic site characterization data for lifelines and other applications - A 50 year retrospective in Los Angeles, CA

The study of the effects of damaging earthquakes on the built environment has made significant strides in the 50 years since the 1971 San Fernando earthquake, particularly in the realm of understanding the effect of geological site conditions on ground shaking. The late UCLA Professor C. Martin Duke was a pioneer in measuring and disseminating data on seismic site conditions at strong-motion stations that recorded the San Fernando event. Duke’s team used geophysical methods to quantify shear-wave velocity (VS), P-wave velocity, and fundamental site period (T0) and disseminated the data in a series of UCLA Engineering reports. Major subsequent efforts by the U.S. Geological Survey, State of California public agencies, the Resolution of Site Response Issues from the Northridge Earthquake (ROSRINE) project, private industry, and numerous individual investigators have rendered the basins and mountainous areas of southern California as among the best characterized for seismic conditions world-wide. This data is instrumental for the development of semi-empirical ground motion models and studies of site response, ground failure, and soil-structure interaction. In this historical overview of seismic site characterization data collection in the greater Los Angeles region, we describe various geophysical methods that have been deployed over time, and the evolution of data quantity and quality to the present. We also present an ongoing endeavor that has developed the United States Community VS Profile Database, which provides an open-access platform for the dissemination of seismic site characterization data. Elements of this database in the greater Los Angeles region will be described, and examples will be provided demonstrating how these data are used in both research and industry practice.