千葉県山武巿蓮沼高感度地震観測井の孔井地質と地質年代

摘要

The Hasunuma seismic observation well was drilled to 1,661m in depth at the central part of the Kujukurihama lowland, Sanbu City, Chiba Prefecture, central Honshu, Japan. Fifteen spot core samples were collected at 50-200m intervals. Geophysical logging was conducted to measure in-situ physical properties of rocks such as P-wave velocity and density. According to the lithologic description and the biostratigraphy of the core and the slime samples, the borehole geology was divided into three formations in descending order ： Holocene strand-plain deposits (0-30m in depth), Plio-Pleistocene Kazusa Group (30-1,584m in depth) and pre-Neogene basement rocks (1,584- 1,661m in depth).%関東平野北東部,千葉県山武巿蓮沼において,深度1.661mの中深層観測井が掘削された.ボーリング孔では50-200m間隔で合計15層準からスポットコァを採取した.また,孔内物理検層から地震波速度や密度といった岩石物性を現位置で測定した.コアやカツティングス試料の岩相および微化石分析結果から総合的に判断すると,本観測井の地質は完新統の浜堤堆積物(深度0-30m),鮮新統〜更新統の上総層群相当層(深度30-l,584m)および先新第三系基盤岩類(1,584m以深)に区分される.