STRUCTURAL RESPONSE TO 3D SIMULATED EARTHQUAKE MOTIONS IN SAN-BERNARDINO-VALLEY

Structural response to one- and three-dimensional (3D) simulated motio ns in San Bernardino Valley, Calif., from a hypothetical earthquake al ong the San Andreas Fault with moment magnitude 6.5 and rupture length of 30 km (18.6 mi) is investigated. For three stations that are close to each other and to the fault line, various measures of ground motio ns (e.g., peak values, intensities, durations, and effective frequency bands), elastic and elastoplastic response spectra, and the response of a 10-story, three-bay frame are calculated. Because the simulation results are reliable up to 1 Hz, only long-period structures, with per iods of 1 to 10 sec, are considered. The results show that the ground motions and the structural response vary dramatically with the type of simulation and the location. In general, one-dimensional (1D) simulat ions underestimated the response and resulted in values as low as one- fifth of those of 3D simulations. The difference in the structural res ponse at three stations was found to be as high as a factor of six. Th e reasons for such large differences are the trapping of seismic waves in the basin and the constructive interference of surface waves trave ling in different directions, none of which can be accounted for by 1D models, and the strong influence of source directivity.