Elucidation of inland tectonic stress distribution based on in-situ crustal stress measurements by means of DRA method

2021 Fiscal Year Final Research Report

• Project/Area Number: 19K04045
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 17040:Solid earth sciences-related
• Research Institution: National Research Institute for Earth Science and Disaster Prevention
• Principal Investigator: Kentaro Omura 国立研究開発法人防災科学技術研究所, 地震津波防災研究部門, 特別技術員 (90399361)
• Project Period (FY): 2019-04-01 – 2022-03-31
• Keywords: コア変形法 / 原位置地殻応力 / 岩石コア / 広域応力場 / 地震観測井

Outline of Final Research Achievements

In-situ crustal stress is an important factor to understand earthquake mechanism and tectonic activities. However, the reliable in-situ stress data down to more than 100m depth seems to still be poor, because complicated procedures are necessary for measurement in a borehole. We tried in-situ crustal stress measurements at deep seismic observation wells, applying DCDA (Diametrical Core Deformation Analysis) method to recovered rock core samples to estimate stress values. DCDA method measures the circumferential diameter variation due to stress relief after the core recovery, and use elastic constants of the rock core.
Present studies suggest a pair of DCDA method by recovered rock core and borehole breakout observation by borehole wall image logging is recommended to measure both of value and orientation of in-situ crustal stress in the case of borehole breakout is produced.

Free Research Field

地球内部物理学

Academic Significance and Societal Importance of the Research Achievements

地殻の原位置地殻応力(絶対応力)は地震発生過程やテクトニック変動を理解する上で，最重要な物理量である．しかし，従来，測定手法の困難さもあって，圧倒的に測定データが乏しかった．本研究では，これまでの手法に比べて，手間の少なく，単純な理論にもとづく手法であるコア変形法による原位置地殻応力測定を実施した．その結果，深部掘削がなされ，岩石コアが採取，保管されていれば，原位置地殻応力の値を測定できることがわかった．今後，他の観測井でも同様の手法により，日本列島広域での原位置地殻応力の測定に向けた先導となった．