SURVEY ON UNDERGROUND SOIL STRUCTURE OF THE FUKUI PLAIN THROUGH MICROTREMOR AND GRAVITY OBSERVATIONS

Abstract

A dense microtremor H/V and gravity observation were done on the line from the north to the south on the west part of the Fukui Plain in order to obtain two dimensional underground soil structures for interpolating four site data surveyed previously by microtremor array observation. The gravity observation was done also in the mountainous districts in the east and west areas where bedrock was outcrop. A simple method being able to deduce the soil structure from the surface to the depth of seismic bedrock by simulating two kinds of peak frequencies of the microtremor H/V spectra with those of the Rayleigh wave fundamental amplitude mode ratio spectra was proposed. It was confirmed that the two dimensional underground soil structures obtained through the H/V and gravity surveys interpolated roughly the array observation results.