| 講演要旨(和文) | | 空中重力偏差法探査法は、地熱資源探査では断裂帯分布推定に利用できる。短時間に細かいデータ間隔にて広範囲な測定が可能な，空間的高密度なデータ取得できる空中重力偏差法探査への期待は大きい。地熱資源は主に山岳地帯に偏在する。重力偏差値は，測定点と質量異常点との距離の逆数の3乗と質量異常値差の積に比例する。急峻かつ凸凹した地形変化のみならず，変質帯や溶岩・貫入岩分布により表層密度や層厚が大きく変化することから，これらの変化にも影響される。表層補正の第1ステップとして,地形データと測定重力偏差データにつき深部起因の重力的影響を減衰・浅部の影響を抽出するHGGS法フィルター処理を行い，両データのMoving Window相関解析から直接表層密度を算出する方法を考案した。 |
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| | 講演要旨(英文) | | The airborne gravity gradient survey is one of the efficient tools of the geothermal resources exploration. Its measurement can be done at short intervals in the short period of time over wide area and is useful for the assessment of fracture distribution. The geothermal prospecting areas are situated normally in the mountainous areas. The gravity gradient responses are proportional to the product of the third power of the reciprocal of the distance between the measurement point and the anomalous mass, and therefore are affected greatly by both the steep topography and the changes of thickness and density of surface layer due to the hydrothermal alterations, intrusions, lava deposits etc. The new approach, namely the horizontal gravity gradient stack (HGGS), is proposed for the assessment of surface density, and the method is applied with the filtering the horizontal gravity gradient data (Data). The comparison between the HGGS filtered acquired Data and the equivalent calculated response of DEM based surface layer is analyzed for calculation of the surface average density by the moving window correlation (MWC) methods. Its application to the actually acquired Data around the Ogiri geothermal plant in the western Japan is analyzed, and its results fit adequately well for the existing hydrothermal alteration zones as the low surface density area, and the possible prominent distributions of intrusions and lava as the high surface density area. |
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