Secular change of crustal stress

2018 Fiscal Year Final Research Report

• Project/Area Number: 15H02141
• Research Category: Grant-in-Aid for Scientific Research (A)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Geology
• Research Institution: Kyoto University
• Principal Investigator: Yamaji Atsushi 京都大学, 理学研究科, 教授 (40212287)
• Co-Investigator(Kenkyū-buntansha): 大坪 誠 国立研究開発法人産業技術総合研究所, 地質調査総合センター, 主任研究員 (70443174) ; 佐藤 活志 京都大学, 理学研究科, 助教 (70509942)
• Project Period (FY): 2015-04-01 – 2019-03-31
• Keywords: 応力 / テクトニクス / 断層 / マグマ / 双晶

Outline of Final Research Achievements

The author has thrown freeware for the stress inversion of orientation data from dilational fractures open to the public through a webpage of Kyoto University. The author developed the theoretical basis for the stress inversion of calcite twin data, which enabled separation of stresses from polyphased calcite twin data.
The new methods were applied to natural data. Hishikari gold veins showed ore mineralization accompanied by the waning of extensional stress on the franks of a Quaternary rift. It was shown that the ore mineralization was accompanied by the repeated formation and break of pressure seals. Igneous dikes in Akita and Hyogo Prefectures indicated weak extensional stress just after the end of the Japan Sea opening. Normal faulting stress regime was determined from quartz veins, indicating extensional stress condition in the forearc region at the time of Japan Sea opening and of the juxtaposition of Southwest Japan with the Philippine Sea Plate.

Free Research Field

地質学

Academic Significance and Societal Importance of the Research Achievements

地殻応力は活断層の動きを支配する．また，マグマや金属鉱床を形成する熱水など，流体の地下の亀裂を通じた移動にも影響する．したがって，地殻応力の理解が，噴火や地震の災害発生メカニズムの理解を基礎づけ，また，金属鉱床や石油鉱床の探査に役立つ．応力場が頻繁に変化するようでは，活断層とは思われいなかった断層が，突然うごいて地震を起こすこともあろう．
さらにまた，原発の地盤安定性や核廃棄物の地下処分を考えるうえで，10万年またはそれより短い時間スケールで地殻応力が安定か，そうではければどれくらい変化するのかを知ることが不可欠である．