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Research on three-dimensional in-situ stress state using drilling core samples

The state of stress in the earth’s crust is a fundamental and important parameter that is closely related to themes such as the mechanism of major earthquakes and the shale gas.

In our laboratory, we are trying to understand the state of crustal stress by focusing on the ASR and DCDA methods, which are the measurement methods using drilled rock core samples.

We have measured stresses on the Nankai Trough and Nojima fault and various oil wells to clarify the stress state. We will continue to explore the mysteries of the Earth from the perspective of crustal stress.

Drilled rock core sample used for core-based stress measurement
Drilled rock core for ASR method

Evaluation of physical properties of rocks

In addition to the exploration and development of the earth’s resources, knowledge of the physical properties of rocks is essential for understanding the fault motion that causes earthquakes. In particular, the evaluation of drilled core samples and well logging data is more accurate than geophysical surveys, and is important as a basic research for advanced simulations. We are evaluating the resistivity and thermal properties of wells drilled on the Futagawa Fault, which is believed to have caused the Kumamoto earthquake in 2016, and have started to develop a measurement method to enable measurements under various conditions.

The measurement sample
Fault deformed ground surface
(Mashiki Town, Kumamoto Prefecture)

Estimation of temperature and other properties distribution for geothermal resources at a great depth

Supercritical geothermal resources, which are thought to exist at a great depth, have more energy than ever before, and their development is expected to enable large-scale power generation with low CO2 emissions. Although the evaluation of physical properties such as temperature is indispensable for the development of geothermal resources, it is difficult to select a specific drilling site due to the lack of in-situ log data and the uncertainties in deep geological data. Therefore, we are developing a method for geothermal resource evaluation with consideration of uncertainties using Bayesian inference and geophysical models based on logging and geophysical survey data acquired in geothermal regions. We are also evaluating the methodology by applying it to promising geothermal resource areas.

Conceptual diagram of a deep geothermal system in the Tohoku region
(Okamoto et al., 2019 Geothermics)

InSAR解析を用いた2018年大阪北部地震前後の地表変動の観測

地震による地すべりなどの地表変位は、地下応力状態や地下の地質構造に関係しています。地殻の状態と地震による影響を理解するために表面変位の監視をすることは重要です。干渉合成開口レーダー(InSAR)は、衛星画像に基づいて表面変位を検出し、監視することができます。2018年6月18日、日本の大阪平野の北東端に沿って、地表面から深さ約12 kmでM w6.1の大きさの大阪北部地震が発生しました。この領域における地震前後の地表変位は、これまでのいくつかの研究で分析されています。一方、地震前後の「長期的な」地表面変位を解析した先行研究は少ないです。この研究では、地震によって引き起こされた地表面変位を検出するために、2018年7月から2019年2月に取得されたALOS-2 / PALSAR-2画像のInSAR解析を使用して表面変位をマッピングしました。

Publication:American Geophysical Union, Fall Meeting 2019, abstract #G13B-0531
有馬高槻断層における衛生視線方向の地表面変位