Prediction of Seismic Response of Long-Period Structures

This paper describes the application of an analytical method for estimating structures at an intermediate distance from a fault; the method is based on fault dislocation and surface wave theory. For illustration, a potential large earthquake which may occur along the southern portion of the San Andreas fault in California is considered. The prototype event assumed is the 1857 Fort Tejon earthquake. As a site, Long Beach is chosen. Long-period ground motions due to Love waves and their response spectra are calculated for various fault rupture and crustal models. Sloshing wave heights in a large tank during the earthquake are also estimated. The results obtained indicate that: (1) the average velocity response spectra of ground motions with 5% critical damping are nearly uniform (30 to 40 cm/sec) over the period range from 6 to 14 sec; (2) sloshing wave height in a large tank is about 70 cm and may reach 2 m under certain circumstances; (3) the freeboard height specified in current aseismic design appears to be inadequate for sloshing waves produced by a large earthquake. The example discussed herein is just one of a number of potentially important applications of the theory.