Journal of Natural Disaster Science

PRELIMINARY ANALYSIS OF NON-LINEAR SITE EFFECTS AT PORT ISLAND VERTICAL ARRAY STATION DURING THE 1995 HYOGOKEN-NAMBU EARTHQUAKE

Jorge AGUIRRE
Graduate Student, Disaster Prevention Research Institute, Kyoto University
and
Kojiro IRIKURA
Professor, Disaster Prevention Research Institute, Kyoto University

(Received 27 February, 1995 and in revised form 6 April, 1995)

Abstract

A preliminary analysis was made of the propagation of seismic waves in a vertical array during the 1995 Hyogoken-nambu earthquake (MJMA=7.2). The vertical array is located on reclaimed land called "Port Island" about 17 km from the epicenter. We used the 1D Haskell linear method to simulate the motions at surficial stations (32, 16, and 0 m) from the imposed motion given by records at the deeper station at 83 m, The linear simulation satisfactorily explains the vertical component of the observed motions; but, both observed horizontal components are overestimated. Non-linear simulation was done to explain the behavior of the horizontal components. We used the finite-difference technique and step by step time integration for this simulation. With this method, the simulated and observed horizontal components are in good agreement, showing the strong influence of the non-linear effect in the horizontal components and the linear amplification of the vertical components. This provides a good explanation of why the vertical motions had disproportionate large amplitudes in comparison with the horizontal ones.

Key words

non-linear site effects, 1995 Hyogoken-nambu earthquake, Port Island, vertical array station