Bayesian Statistical Development of Microseismic focal mechanism Inversion with Well Logging Geophysical Data

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K05394
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 31020:Earth resource engineering, Energy sciences-related
• Research Institution: Tohoku University
• Principal Investigator: Mukuhira Yusuke 東北大学, 流体科学研究所, 助教 (60723799)
• Co-Investigator(Kenkyū-buntansha): 吉田 圭佑 東北大学, 理学研究科, 助教 (20743686)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 坑井検層 / 誘発地震 / ベイズ統計学 / 断層面解 / 群発地震 / 流体量

Outline of Final Research Achievements

(1) An attempt to directly incorporate geophysical information (e.g., crustal stress) obtained from well logs into MT inversion and to constrain the solution by Bayesian statistical inversion method for microseismic events did not necessarily produce the expected results, partly due to the quality of the microseismic data used.
(2) We applied the physical model that links seismic activity to the amount of fluid involved, which has been proposed in the field of resource engineering based on geophysical information obtained from well logging, to subduction earthquakes to identify the amount of fluid that is considered to be a factor in the seismicity.
We proposed a new approach to quantify the fluid with unprecedented temporal and spatial resolution to elucidate the fluid dynamics in subduction zones, and demonstrated the usefulness of this approach.

Free Research Field

地球物理学

Academic Significance and Societal Importance of the Research Achievements

(1) 高品質の微小地震データと，地殻応力（絶対値・方向）が全て揃う例は，中々稀であり，今後の様々なフィールドからのデータの蓄積が待たれる。微小地震はマグニチュードが小さく，中々波形の振幅情報を完全に使いづらいが，本研究で目指した方向性は，以前有効であると思われる。
(2) 2011年3月に山形-福島県境で発生した群発地震について、群発地震発生前に地殻内に蓄積されていた流体量を推定した結果，流体量を具体的に定量化できた。この様な，浅部近くに流体として貯留されていた水の，定量的な推定は世界で初めての試みである。さらにこの推定量を基にM9クラスの地震，鉱脈生成とのリンクなど新たな議論が展開できた。