The October 1, 1987 Whittier Narrows earthquake generated strong ground motions that were recorded by numerous accelerograph stations throughout southern California. One station, located in Tarzana, approximately 44 kilometers west of the earthquake's epicenter, recorded unusually high peak accelerations. The peak accelerations, which are high frequency motions, are between 4 and 10 times greater than the peak accelerations recorded at nearby stations. The Tarzana accelerograph was calibrated shortly after the earthquake, and no indication of instrument malfunction was apparent in the strong motion accelerogram. This research project will investigate this anomalously high acceleration recording, on the supposition that it was a result of soil-structure interaction between the accelerograph station and the soil in which it is embedded. Such an effect was found to exist in an earlier study by the principal investigator at an accelerograph station that had a number of design features in common with the Tarzana station. The purpose to this study is (1) to determine the extent of any soil- structure interaction that may have contributed to the large recorded accelerations, (2) develop reliable analytical models to predict the soil-structure interaction effects at this station, and (3) remove the soil-structure interaction effects from the accelerogram to obtain the free-field motion.
