地质调査研究报告BulletinoftheGeologicalSurvey.PDFVIP

Susumu Tanabe, Toshimichi Nakanishi, Katsumi Kimura, Shoichi Hachinohe and Toshio Nakayama (2008) Basal topography of the Alluvium under the northern area of the Tokyo Lowland and Nakagawa Lowland, central Japan. Bull. Geol. Surv. Japan, vol. 59(11/12), p. 497-508, 4 fi gs, 1 table. Abstract: In this study, we identifi ed the basement of the latest Pleistocene to Holocene incised-valley fi lls (Alluvium) from 7,021 borehole logs in the northern area of the Tokyo Lowland and Nakagawa Lowland. We constructed the dataset, which consists of the latitude and longitude of the borehole site and depth of the Alluvium basement. The depth-distribution map of the Alluvium was illustrated based of this dataset and interpolation of the Alluvium depth distribution by the inverse distance weighting method. We assumed the top of the Basal Gravel of the Alluvium as the basement of the Alluvium where the Basal Gravel exists. This depth-distribution map illustrates a detailed topography of the Nakagawa, Moto-arakawa, Ayasegawa, Arakawa and Paleo-Tokyo River Valleys, buried terraces and buried wave-cut benches. The comparison between the thickness of the Alluvium and surface elevation in the northern area of the Tokyo Lowland and Nakagawa Lowland indicates that there are major relationships. The elevation is less than T.P. +2 m in the area where the Alluvium thickness is more than 40 m, and the elevation is more than T.P. +2 m in the area where the Alluvium thickness is less than 25 m. Keywords: Alluvium incised-valley, basal topography, Tokyo Lowland, Nakagawa Lowland, Holocene