重力変化を説明できるTRIES・MIU周辺の地下水流動モデル

Water flux model around TRIES/MIU to explain the gravity change

本多 亮*; 大久保 慎人*; 田中 俊行*; 柳澤 孝一

Honda, Ryo*; Okubo, Makoto*; Tanaka, Toshiyuki*; Yanagizawa, Koichi

The absolute gravity measurement by FG-5 has been operated in and around the Tono Research Institute of Earthquake Science (TRIES) since 2003. During this period, two types of ground water level change was observed. One is the water level decrease more than 70 m in 12 years, which along the drilling of the 500 m deep shafts of the Mizunami Underground Research Laboratory (MIU). The interspaces of these stations are 1 to 2 km. The coseismic gravity decrease in these stations were about 10 micro gals which suggest that the mass moved away from these three stations equivalently. Based on former researches of geology and hydraulic geology, which clarified the permeable and impermeable layers well, we reached the model as follows for the coseismic case.