Study on the Subsurface Thermal Structure at the Sendai Plain. 1. Construction of 3D regional groundwater flow and heat transport model:1. Construction of 3D regional groundwater flow and heat transport model

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We obtained 16 temperature-depth profiles and other hydrological data by field measurement in the Sendai Plain, Northeast Japan to understand hydrogeological regime and subsurface thermal effects. Subsurface temperature in the Sendai Plain is around 14°C in the whole Quaternary system and its thermal gradient is very small, while the Tertiary system has a larger thermal gradient of 3.5°C/100m. Chemical compositions and stable isotopes data (δ D and δ<SUP>18</SUP>O) of the groundwater indicate that the groundwater flow system has marked difference between in the Tertiary and the Quaternary systems. In the Quaternary system, where the groundwater flows in a local scale, downward flux caused by groundwater recharge is dominant. Therefore, downward heat transport due to advection from surface may constrain upward terrestrial heat flow. Moreover, subsurface temperature distribution in the Quaternary system is hardly distorted because groundwater flows to the Sendai Bay horizontally. In the Tertiary system, on the other hand, groundwater flow system is regional and upward terrestrial heat flow is dominant factor in the subsurface thermal regime. 3-D groundwater flow and heat transport model of the Sendai Plain shows that the change of thermal gradient near the basement of the Quaternary system can be explained by a hydrological effect.
日本地熱学会の論文