SIMULATION OF SITE AMPLIFICATION FACTORS OBTAINED FROM BOREHOLE RECORDS CONSIDERING BOTH TWO-DIMENSIONAL EFFECT AND NONLINEAR BEHAVIOR OF SOIL SEDIMENTS : Analysis of weak motion and strong motion observed at a vertical array at Kuno district in the Ashigara Valley

Abstract

We studied amplification characteristics of soil sediments by using strong and weak motion records observed on the surface, at 30m below, and at 97.6m below the surface at Kuno district in the Ashigara Valley. We found that the amplification factors for the main part of the weak and strong motions can be simulated from the one-dimensional soil analysis by considering the non-linear behavior of soil sediments during the strong motion shaking for not only alluvial surface layers but also diluvial layers. In order to simulate the amplification factors better, we performed two-dimensional finite element soil analysis in which we assume a soil model whose thickness of the first surface layer at the observation site is 8m and that at 50m away from it is 6m. As a result, we could simulate the amplification factors more precisely, because the short period surface waves whose Airy phase has about the period of 0.5 sec are generated due to such a small irregularity of the surface soil sediments.