| 講演要旨(和文) | | 鳥海山に降った雪や雨による地下水が，多孔質の溶岩を伝って日本海の海岸で湧水となって現れる場所のひとつが山形県遊佐町の釜磯海岸である．釜磯海岸では，実際に砂浜からの複数の湧水口を目にすることができる．湧水となって地上に現れる前の地中の「みずみち」を可視化する目的で物理探査を行った．多周波数電磁センサーGEM-2による電磁探査，磁気探査，多電極電気探査（ERT）を実施したところ，特に電気探査が，湧水に関連する浅部の地下構造を推定するのに有効であった．今回は，電極配置として，ダイポール・ダイポール法とポール・ポール法を用いた．地下構造解析の結果，砂浜の下には溶岩起源の地下水を通しにくい岩塊が存在し，これらの岩塊の存在位置が，地表近くの地下水の経路をコントロールしているものと考えられる． |
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| | 講演要旨(英文) | | Ground water in Chokai volcano slowly flows inside the fresh porous lava. The ground water is upwelling around the end of the lava flow near the coast of the Sea of Japan Tens of small spring can be seen at Kamaiso sand beach, Yuza town, Yamagata Prefecture. We carried out geophysical exploration s such as induction method, magnetic survey, and ERT (Electric Resistivity Tomography) at the area surrounding springs Using the portable electromagnetic exploration instrument called GEM 2, shallow structure of the electric conductivity was estimated. In spite of careful noise reduction, the conductivity structure might be contaminated by artificial electromagnetic noise or metal facilities above the ground. Magnetic anomaly can delineate the lava rocks buried in the beach sand. We adopted the dipole dipole array and the pole pole array in ERT. The resistivity structure estimated by ERT up to the depth of about 15 m by the dipole dipole array and to the depth of about 40 m by the pole pole array. We can estimate the path of upwelling water beneath the spring. At the shallowest path of the water is thought to be controlled by the location of solid lava rocks. |
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