Journal of Natural Disaster Science

A CONSIDERATION OF AMPLIFICATION CHARACTERISTICS OF IRREGULAR GROUND IN THE TOKYO AREA

Shigeru NODA
Associate Professor, Department of Social Systems Engineering, Tottori University, Tottori

(Received 3 September 1993 and in revised form 28 January 1994)

Abstract

The most realistic approach to microzonation is to determine empirical site-amplification factors and to correlate them with the various geotechnical parameters of the site. The effects of an irregular soft ground layer on site-specific amplification factors are discussed. Five kinds of geological structures having different soft-layer thicknesses that are found in the Tokyo area are analyzed. Ground motions were obtained by the finite element method (FLUSH). The vertical incident waveforms used were the El Centro and Hachinohe records. Resuits show that 1) ground motion were affected not only by local irregularities in the ground structure just below the observation point but by distant irregularities as well; 2) the frequency characteristics of the input waveform have a marked influence on site-specific amplification factors of peak amplitudes.

Key words

irregular ground, amplification factor, Tokyo area, nonlinear response analysis, microzonation