人工地震による首都圏南西部の地下深部探査

夢の島-江の島測線の地下構造

抄録

It has been frequently said that seismograms obtained in Tokyo contain rather long-period components in themselves. Authors pointed out the importance to make clear extensive and deep underground structure of the Tokyo Metropolitan area, based on the experience on simultaneous observation of earthquake ground motions under the different kinds of geological conditions.
In this paper, results on the seismic prospectings in the southwestern part of the Tokyo Metropolitan area were presented. Outline of the interface between sedimentary layers and the uppermost layer of the earth's crust was shown in the form of “time-term”, along the line stations from Yumenoshima, Tokyo to Enoshima, Kanagawa. The length of this line was almost 50 kilometers long.
From the distribution of those time-terms, it was made clear that the interface mentioned above changes its depth more remarkably and rapidly, in comparison with those which obtained in other parts of the Tokyo Metropolitan area by many researchers. Most of all, Enoshima and its vicinities were confirmed to be situated on the boundary which distinguishes inner sedimentary zone of the Kanto Plain from outer outcrop zone of firm substratum.
From these results, the mechanism of formation and propagation concerning rather long-period earthquake ground motions can be expected to be elucidated.