京葉臨海地域における常時微動による地盤環境区分  [in Japanese] Ground classification by microtremors observation in Keiyo coastal area  [in Japanese]

This surveyed area is located in the western parts of Chiba prefecture, facing Tokyo Bay. The rapid urbanization of the area has been brought forth the reclaimed land on the shore and the artificial landforms on the upland. Central and southern parts of the reclaimed land have been developed as industrial complex. Northern parts of the reclaimed land and upland have been developed as residential area. But a large earthquake has not hit the area, recently. An observation of the microtremors was carried out at 610 points in the area, in order to elucidate ground characteristics. Then power spectra of the observed records were analyzed by F.F.T Analyzer. A predominant frequency at each observation point is obtained from the spectrum. These spectra are classified into 5 types from Type I to Type V by difference of a spectrum shape. From the two above-mentioned viewpoints, the ground classification of the area were carried out. The main results are as follows: 1) Zones of predominant frequency, "〜2 Hz" and "2 Hz〜2.5 Hz", are distributed in the reclaimed land alluvial plain and artificial landforms. The spectra of "〜2 Hz″ zone are classified into Type I or Type II. The spectra of "2 Hz〜2.5 Hz" zone are classified into Type II or Type III. 2) Zones of "2.5 Hz〜3 Hz" and "3 Hz〜3.5 Hz" are distributed widely in this area. These spectra are classified chiefly into Type III. 3) Zone of "3.5 Hz〜" is distributed in apart of diluvial upland. These spectra are classified into Type III or Type IV.