63.深井戸地震計による観測(第2報) : 千葉県日内村天然ガス井戸における地震観測

概要

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Earthquakes were recorded in a gas well which was deeper than that of Nokogiriyama in Chiba and of Kongo in Tokyo previously reported. The observation was made at a depth of 796.2m in a 1750m-well. The instruments used here have been described in our previous report. The data were recorded on a small-size magnetic data recorder with a direct recording system specially designed for microearthquake observation, total magnification being 2×105 in the well and 2×104 on the surface. The observation gave the following results. 1. The amplitude of ground noises on the surface was about 10 times larger than in the well for the frequency range from 5 cps to 30 cps. However, the earthquake motions were also enlarged on the surface and finally the signal-noise ratio was slightly larger at a depth of 796.2m than on the surface. 2. The earthquake recorded in the well had wider band spectra in comparison with those on the surface.
1969-03-17