The SCEC Phase III Strong-Motion Database

by Jamison H. Steidl and Yajie Lee

Abstract

As part of the Southern California Earthquake Center (SCEC) Phase III effort to include site effects in hazard models for southern California, a regional database of strong-motion observations was developed. The observations consist of the peak ground acceleration (PGA) and 5% damped response spectral acceleration (SA) at 0.3-, 1.0-, and 3.0-sec periods from 28 earthquakes and 281 stations. A total of 449 pairs of horizontal PGA and SA observations that were taken from the SCEC Strong-Motion Database (SMDB) are presented here. The phase III database includes earthquakes with moment magnitudes larger than 5.0 and stations in southern California with locations between 32^o and 36^o north latitude. Observations from buildings with more than two stories and dam abutments or crests are excluded from the database. Observations with distances of 150 km or greater were also excluded. The agencies that provided the data to SMDB are the U.S. Geological Survey, California Strong Motion Instrumentation Program, University of Southern California, and the Los Angeles Department of Water and Power.

The database also contains site classification information for each station. A first general classification is based on the 1:750,000 California map of Quaternary, Tertiary, and Mesozoic geologic units by Jennings (1977) as modified by Park and Elrick (1998). A second more detailed classification is based on Quaternary mapping in the Los Angeles region by Tinsley and Fumal (1985) as modified by Park and Elrick (1998). A third classification is based on the correlation of surface geology with shear-wave velocity in the upper 30 m (Wills et al., 2000). An arbitrary “depth-to-basement” parameter is assigned to stations that are located within the boundary of the 3D velocity model used by Olsen (2000), which is based on the SCEC 3D velocity model (version 1). This parameter is defined as the depth to the 2.5km/sec velocity isosurface. Special parameters associated with particular attenuation relations, such as different distance measures, a hanging wall flag, and fault-type flag are also assigned to each observation. These data are all presented within the tables and figures of this article, and also have been made available via a downloadable file on the Internet (http://smdb.crustal.ucsb.edu/~phase3).

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