| 講演要旨(和文) | | 電気探査や電磁探査が海底熱水鉱床周辺で行われてきたが，海底熱水鉱床周辺での比抵抗構造や分布は明確には得られていない．そこで，本研究では，深海曳航式海底電気探査法に注目し，海底熱水鉱床の比抵抗構造を明らかとすることを目指す．比抵抗構造を求めるための逆解析は，平滑化制約項が一般的に用いられている．しかし，熱水鉱床は局所的に濃集して存在していることが知られている．そのため，平滑化制約項を用いた逆解析では，濃集がぼやけた結果として求められる．そこで，急激な比抵抗の変化を再現する事ができ，更に，岩石物性値を組み込む事ができるFCM クラスタリング項を目的関数に追加した．その制約項を組み込んだ逆解析を仮想データと実データに適用した結果から，本逆解析技術を使用した曳航式電気探査法は，海底熱水鉱床周辺での海底下の比抵抗構造を推定することに有効であることが示された． |
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| | 講演要旨(英文) | | SMS (Seafloor Massive Sulfide) deposits, including rare and precious metals, have been found in the vicinity of hydrothermal active areas. Geophysical explorations with electromagnetic (EM) methods have been carried out around SMS deposits because SMS deposits are known as low resistivity material. However, resistivity structures below hydrothermal active areas have not been clearly investigated. In this study, we focus on a marine deep-towed DC resistivity survey as an effective tool to the exploration of SMS deposits. The drilling surveys have illustrated the real distributions of SMS deposits are concentrated at narrow (thin) zones. Therefore, we add the Fuzzy C-Means (FCM) clustering constraint into the objective function in the inversion procedure to obtain the sharp-change of resistivity matching given the petrophysical information. The refined inversion results show that the inversion using the FCM clustering constraint can produce the sharp boundaries in resistivity structure, which can incorporate the realistic petrophysical information. We applied the inversion code to the field data obtained at the Okinawa Trough and the inverted resistivity anomalies are consistent with the geological investigations of the hydrothermal fluid flows and the observed distributions of seafloor venting sites. |
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