APPLICABILITY OF EMPIRICAL GREEN'S FUNCTION METHOD TO STRONG MOTION RECORDS ON MAN-MADE ISLAND IN KOBE

摘要

Empirical Green's function (EGF) method has been applied to the records at Port Island during 1995 Hyogo-ken Nanbu Earthquake and it's aftershocks to evaluate the nonlinear effect on the mainshock records with special attention to two distinguished phases which are estimated to represent direct S wave and reverberating S wave inside the basin. Kamae and Irikura's source model has been adopted. The results can be summarized as follows. 1. Direct S phase during the mainshock can be successfully reproduced with EGF method by taking into account the nonlinear behavior of the local soft soil layers above GL-83m. 2. On the other hand, the second phase seems to have already lost approximately 60% of it's amplitude before it's incidence to Port Island due to nonlinearity. This loss of amplitude may be attributed to the non-linear soil behavior during it's first reverberation on the free surface. Nonlinear ground response analysis shows that this kind of amplitude reduction during reverberation can exist under certain condition.