マルチフィルターによる地震動の非定常相互スペクトル特性の解析

Abstract

Consideration of Nonstationary correlation in multivariate and multidimensional earthquakemotions is important in the design of large foundations and spatially extended structures.In this study, an effective technique for the nonstationary cross spectrum of multidimensionaland multivariate earthquake motions is developed by multifilter technique, which is anextension of nonstationary power spectrum analysis proposed by Kameda. The multifiltertechnique has advantages such that the resolution of spectral components in time and frequencydomain is better than that of repeated Fourier transformation and band width in frequencydomain is proportional to the frequency.Two parameters, that is, damping parameter and smoothing parameter in time domain, are decided by numerical calculation using some Japanese strong motion records. We discussthe physical meanings of nonstationary coherency and phase differences which are obtainedfrom nonstationary cross spectrum. In numerical examples, the nonstationary coherency andphase differences are calculated using SMART-1 array data in Taiwan. On this basis, thevalidity of the technique proposed herein is examined and some discussions are made onnonstationary coherency and phase differences of multivariate earthquake motions.