報告書番号

N05026

タイトル（和文）

マグマの水平移動に対する評価法の提案 -- 隠岐島前火山の火道分布に基づく化学組成の影響の検討 --

タイトル（英文）

Proposition of assessment method for lateral magma migration.- Effects of magma geochemistry studied from the distribution of conduits at Oki Dozen volcano. -

概要 （図表や脚注は「報告書全文」に掲載しております）

地質環境の安定性に関わる評価では，地表の火口分布に加え，地下のマグマが火山から遠方まで到達することや，マグマの移動方向が変化する現象に対する，評価法を開発する必要がある．隠岐島前火山を対象とした調査と，文献研究に基づき，マグマの水平移動に影響する要素を整理した結果，マグマの化学組成・活動規模・応力場の性質・地質構造の4項目が重要であることを明らかにした．これらの成果に基づき，マグマの水平移動を主に方位の観点から評価するための評価法を提案した．マグマの潜在的水平移動を評価するためには，まず，火山の形成史，地質構造や広域応力場を調査し，上記の4項目に関し起こり得るマグマ移動の事象を把握する．このように将来的な火山活動の位置を推定，評価したうえで，評価対象地域との位置関係により，その影響を評価するという手順を提案した．

概要 （英文）

The lateral migration of magma as dikes within crust that result in parasite vent formation is common volcanic activity. It is highly important to evaluate the occurrence of such activity around the volcano for assuring the long-term stability of the HLW geologic disposal site. The geological and geophysical conditions that affect magma migration are determined by studying the parasite vent distribution of volcanoes located at different stress conditions. The conditions that affect magma migration are (a) geochemistry of magma, (b) volcano edifice growth, (c) relation between the local stress field and regional stress field, and (d) geologic structures. The effect of geochemistry is found in the distribution of conduits at Oki Dozen volcano. The comparison between the mafic and silicic dikes, sills and parasite cones show that the mafic magma is more likely to migrate to particular orientation, while the silicic magma is more likely to change migration directions. The local stress field is formed by the magma activity: therefore, its extent is likely to change with the development of volcano edifice. Migration of magma is more likely to occur in differential stress regime, to the directions of maximum and minimum lateral stress. The conditions (a)‐(d) affect migration direction; therefore, it is important to evaluate the lateral migration direction. It is proposed that determination of the above conditions be included in the evaluation process for geologic disposal, and volcanic hazard assessment in general.

報告者

キーワード