Tokyo Bay is at the receiving end of the groundwater flow system of the Kanto Plain, Japan’s largest plain and groundwater basin. The groundwater flow, from mountains surrounding the Kanto Plain to Tokyo bay, is thought to run along the geological structure of the tectonic basin. Therefore, water discharged into the bay may contain information concerning deeper zones of the Kanto Plain.
Groundwater samples were collected around the bay from 25 to 2000m depth wells, and isotopes (Carbon, Oxygen and Hydrogen) and general water quality were analyzed. The deep zone water was determined to be composed, for the most part, of rainwater and fossil seawater. This suggests that rainwater filtered down to the deep zone on short term, that fossil seawater still exists in that zone, and further suggests that these characteristics of water reflect the geology (history) of the Kanto Plain. This study contributes to existing data of deep zone groundwater around the Tokyo Bay, and should serve further applied research or planning.
