| Title | 3D Temperature Modeling over Kyushu Island (SW Japan) and Its Characterization from Geologic Structures |
|---|---|
| Authors | Naoyuki Tadakuma, Katsuaki Koike, and Hisahumi Asaue |
| Year | 2010 |
| Conference | World Geothermal Congress |
| Keywords | Spatial estimation, well-logging data, active fault, tectonic line, active volcano, fluid flow pattern |
| Abstract | Three dimensional (3D) temperature distributions down to deep depths are important for exploration and assessment of geothermal resources. With the rapid development of computer capability and the increase of open sources of geoscience data, such temperature modeling has been executable for multiple purposes. This study is aimed at developing a method for accurate 3D temperature modeling using an open access database over a wide area by selecting Kyushu Island, southwest Japan as a study area. The modeling was targeted for a rectangular solid covering 280 km (E-W), 330 km (N-S), and 1 km along the depth, and was carried out by a spatial estimation technique, 3DOPT using the temperature data by well-logging at 202 sites and the thermal gradient data at 29 sites. 3DOPT is founded on a mechanical minimization principle similar to spline methods. The resultant 3D model clarified plausible characteristics on the locations of high and low temperature zones: high temperature zones up to shallow depths, which are attributable to convective flows, are highlighted in the geothermal areas and near the active volcanoes. Another interesting feature is the continuous low temperature zone along the largest tectonic line (Usuki-Yatsushiro Line) across Kyushu Island and around the active faults, which signifies that the tectonic line and the faults may form high permeable zones by the large fracturing and derive descending flows of the groundwater down to the deep depths. This interpretation can be confirmed by a combination of the groundwater level modeling by co-kriging: the positions of large decline of the groundwater levels correspond with the decrease zones of temperatures at the 1000 m depth. |