10:15 AM - 10:30 AM
[HQR23-02] Distribution of postglacial incised-valley fills beneath Kujukuri Plain, central Japan
Keywords:Kujukuri Plain, Chusekiso, postglacial incised-valley fill, Holocene
Kujukuri Plain, Chiba Prefecture, eastern Japan, is formed as beach ridges prograding during and after Holocene highstand (Moriwaki, 1979). Subsurface strata which is 20m thick from the ground level is composed of beach sand, and topographic relief including incised valleys buried under the sands. The buried topographic relief of offshore in this area has been revealed to some extent by sonic prospecting (Maritime Safety Agency of Japan 2000), whereas those in the land area is almost unknown, except for the southernmost part of the plain (Mobara Area). The topography of buried valley is estimated based on boring log data, which is from Information Bank of Chiba Prefecture (open data) and from local governments (open/closed data). Several axes of incised valleys are located roughly along present rivers. The northernmost one is most wide and deep, which is about 40 m deep at the coastline, and seem to connect with the largest valley offshore. We have the plan of stratigraphic boring surveys in this area for estimation of tectonic movement and geographic development in late Quaternary.