Thermal Gradient Map and Thermal Structural Model. A Case Study of Hokkaido.:A Case Study of Hokkaido

概要

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Thermal gradients were obtained from temperature logging data of 687 drillholes in Hokkaido. Most of the data are from the drillholes for hot spring explorations: A mesh data set of thermal gradientswas created from all of the data of the drillholes through a spatial averaging interpolation algorithm.The map from the mesh data represents a regional geothermal structures of Hokkaido. The high density data coverage of the map also delineates local thermal anomalies of volcanic and geother-mal areas. The first-order thermal structures were calculated based on the following assumptions: (1) 10°C at the level; (2) a one-dimensional and steady state model; (3) a constant thermal conductivity of 2.5 Wm-1K-1 for the upper crust; (4) a constant heat generation of 1.5μWm-3 for the upper crust; (5) existence of partial melting zones. The temperatures at 3 km depth below sea level, depths of isotherm of 200°C, and four thermal corss sections across volcanic and geothermal areas were mapped . The results present local thermal structures of geothermal areas as well as regional structures of the whole Hokkaido area. They are concordant with local thermal structures mapped by reliable temperaturedata of deep drill holes of geothermal areas. The consistency suggests that the temperature data from the drillholes for hot spring explorations give a reasonable geothermal gradient map.
日本地熱学会の論文