| Abstract |
The present paper discusses the temperature field formed by thermal advection in the Tokachi groundwater basin as modeled by the finite element method (FEM). The Tokachi Plain is a tectonic basin located in southeast Hokkaido, the northernmost island of Japan. The plain is divided into tow blocks: an uplifting eastern block and a subsiding western block or main area of the plain, via the Tokachi central fault. Groundwater temperatures to a depth of 300m, groundwater potential distribution and stable isotopic ratios of water in the Tokachi Plain all show that the groundwater is mainly recharged in the surrounding piedmont areas of Mr. Daisetsuzan and the Hidaka Mountains. On the other hand, groundwater of the main area converges radically to the lower places, blocked by the relatively impermeable eastern block and discharges into the Tokachi River. Hot water is located around 1000m depth in the western block, while it exists at a few hundred meters depth in the eastern block/ A few hypotheses have been proposes for the heat source. One is that hot water heated in Mr. Daisetsuzan volcanic zone flows into the groundwater basin. Based on the groundwater temperature distribution, however, this contribution is considered to be slight. The second hypothesis is that groundwater in the western block is heated by an unknown high temperature rock mass which exists at depth in the eastern block, higher temperature zone influenced by the Akan volcanic area. |