論文
溶岩堆積地帯における重磁力探鉱データの総合的解析の適用
2018 年 40 巻 2 号 p. 109-127
詳細
2018 年 40 巻 2 号 p. 109-127
This paper deals with the application of the integrated analysis of gravity and geo-magnetic data on the lava dominated deposited area in the Kuju geothermal prospective region.
The gravity/geo-magnetic relationship in and outside of the depression can be characterized and separated in the classified cross-plots of gravity and pseudo-gravity (BG-PsG) data sets by the PsG/G Ratios obtained through the moving window correlation.
The linear line of the BG-PsG relationship which represents the depositions of 100% lava filling in the depression (Maximum Volcanic Line, MVL) can be drawn in the cross-plots of the BG-PsG data sets. The deviation of the measured PsG ( ⊿PsG) from the MVL relates to the content of lava deposits from the adjacent volcanos in the depression. The low ⊿PsG corresponds to the area of the high lava content, while the high ⊿PsG is located in the area of the low lava content and subsequently the high content of such tuff depositions as rocks of less magnetization.
The results show two low ⊿PsG trends, and they correlate satisfactorily well to the high geo-temperature areas defined by the prevailing reports and drilled wells; one being from the Otake/Hatchobaru geothermal area extending toward the NW to the area of Sugawara geothermal plant (GP) and the another being from the Mt. Kuenohira, via Takigami(GP) to Noya region. The high ⊿PsG trend lies between them, corresponding to the low geo-temperature area of the Shishimuta depression.
Considering the depositions of lava tend to fill in such low lands as lagoon, lakes, rivers etc., which is paleogeographically the case in the studied area, the hot water passes acting as geothermal reservoir could possibly be formed by the cool joints when the lava flew in the water of such low lands. This type of geothermal reservoir tends to extend horizontally as referred to the prevailing reports and results of drilled wells, and may form additional geothermal prospects in addition to that of conventional reservoir of vertical fractures.
