報告書番号

N05024

タイトル（和文）

活火山の火口移動に関する検討 -－電力重要構造物の立地に関わる基本的留意点－-

タイトル（英文）

Crater migration of active volcanoes in Japan- Practical issues on the electric facility siting -

概要 （図表や脚注は「報告書全文」に掲載しております）

情報の豊富な国内の6活火山において，火口分布・火山の構造・応力場を調べ，火口移動の特徴と電力重要構造物立地上の留意点を検討した． その結果，（1）火口移動の仕方は，広域応力場と局所応力場の組合せで変化;（2）局所応力場は，火山体の大きさにほぼ匹敵;（3）差応力的な場では，岩脈の水平移動が起こる．高レベル放射性廃物処分事業では，この点は特に留意すべきである;（4）地質構造はマグマの伸展を妨げるバリアの役割が期待できる;（5）単成火山群の成長パターンは，広域応力場と岩脈群が作る局所応力場に支配される．すなわち，極初期の単成火山は広域応力場に従いやすい．以上から，電力重要構造物の立地に際しては，各火山について過去の履歴を詳細に調べ，応力場の基本的性質（圧縮・引張），水平差応力の大きさ，並びに局所応力場の範囲を知る必要がある．

概要 （英文）

The crater migration of volcanic eruption is one of the potential phenomena that may result in striking damage to public facilities, including the electric power facilities. Precise scientific evaluation from potential hazard of the nearest volcanism is also requested in terms of high-level radioactive waste disposal program. Unraveling practical issues with respect to the characteristic variation of volcanic eruption is essential. The characteristics on crater migration within 6 active volcanoes have been examined in terms of growth of volcano structure and associated regime of stress field. The important results and implications are the followings. (1) The behaviour of crater migration can be determined by the combined stress regime between the regional (tectonic) stress field and the local stress field; (2) The area of local stress field is roughly limited within the volcanic piles; (3) The long distance migration of crater likely occurs under the stress regime of wrench faulting (largely differential stress regime), and along the maximum or minimum orientations of horizontal stresses (sHmax or sHmin). The siting at there should be avoided. Particular note for this is required in the site evaluation of high-level radioactive waste disposal program; (4) Subvolcanic structure, such as caldera marginal faults, can be expected as a barrier for the migration of dyke; (5) Growth structure of the monogenetic volcanoes can be determined by multiple intrusions of dykes. Proper evaluation on the eruptive history, the tectonic stress field, the area of local stress field and the maximum or minimum orientation of horizontal stress (sHmax or sHmin) is essential for predicting future activity of the target volcano.

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