ESTIMATION OF QUATERNARY AND S-WAVE VELOCITY STRUCTURE OF IZUMO PLAIN USING MICROTREMORS AND MICROTREMOR ARRAY

Abstract

We observed microtremors at 400 sites and microtremor arrays at 4 sites, in the Izumo plain. S-wave velocity in quaternary and the distribution of predominant periods were determined by microtremor array observation and H/V (horizontal-to-vertical) spectral ratios, respectively. The average S-wave velocity in quaternary was found as 230m/s. The predominant periods in H/V spectral ratios will provide individual thickness of quaternary following to the quarter wavelength law. We estimated the thickest value at about 10 to 100m with the predominant period of 0.2 to 1.8s, and it looked quite reasonable as we confirmed similar result in the geotechnical information.