Abstract
A horizontal orbit of observation in near fault area shows elliptical shape. First of all, we estimated response of base isolation system by a multiple shear spring model for one-directional and bi-directional input motions. We found that the response from bi-directional input show larger amplitude than those from one- directional input in some cases, indicating the importance of the particle orbit characteristics of strong ground motions. Next, we theoretically calculated strong ground motions in near fault area using the wavenumber integration method. As a fault becomes shallow, a horizontal orbit changes from linear shape to ellipsoidal shape. Moreover, we estimated the contribution of near-field term to the change by Green function of elastic fullspace and investigated the effect on two-dimensional response of base isolation system.
