From January to May of 2004, METI/JOGMEC-MH21 prepared the METI Exploratory Test Wells Tokai-oki to Kumanonada, including drillings, loggings, and long-term borehole temperature monitoring by DTS/FBG. A high-resolution geochemical study of interstitial water and sediments was conducted at the Dai-ichi Tenryu Knoll and the Daini-Atsumi Knoll. Cl- baselines (original in situ Cl- concentration) at both sites show contrasting and characteristic patterns. The oxygen isotope compositions of the interstitial water seem to show a symmetrical pattern mirror image similar to the Cl- concentration. T...