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image: Japanese Rapid Drilling Trench (JFAST) project drilling through a plate boundary fault that has ruptured; The research team collected core samples for post-earthquake stress analysis. Show more

Image credit: KyotoU Global Comms/Jake G Tobiyama

Kyoto, Japan – The great 2011 earthquake that triggered a tsunami in northeastern Japan is still remembered for its destructive power.

Also known as the Mw 9.0 Tohoku earthquake, the seismic nature of this disaster was not entirely clear at first. Whereas, earthquakes caused by tectonic stress accumulating in the reverse rift are only partially triggered. In previous studies where full versions have been put forward, the hypothesis was based on earthquake monitoring and simulations, or on direct stress measurement data just above the fault using log data.

Now, a team of researchers at Kyoto University has found evidence that a full-blown release of stress may have contributed to this record-breaking event.

“Slight differences between the maximum and minimum horizontal stresses after the earthquake near the fault indicate that the Tohoku earthquake occurred at full stress release,” explains lead author Weren Lin.

The team found that both sedimentary formations above and below the plate boundary fault underlie the stress state of normal faults in which the vertical stress is greater than the maximum horizontal stress.

“Knowledge about stress changes before and after this earthquake, both above and below a gently sinking fault, can provide us with insight into how fault slip triggered the ensuing tsunami,” says the author.

Lin’s team was able to collect data on the state of stress above the source fault of the Tohoku earthquake, at the boundary between the North American plate and the downsloping Pacific plate. However, geophysical data of the stress state below this region was unreliable.

To address this issue, the team studied one of four drill core samples collected by the Japan Rapid Drilling Project — or JFAST — from below the source fault and was the first to successfully detect the state of stress at this depth.

“Our new data show good consistency with previous above-fault findings, indicating that combining geophysical data with core samples to comprehensively examine stress states is effective.”

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The paper “3D stress state above and below plate boundary fault after the 2011 Mw 9.0 Tohoku earthquake” appeared on November 9, 2022 in Earth and Planetary Science Letters, with doi: 10.1016/j.epsl.2022.117888

About Kyoto University

One of the leading research institutions in Japan and Asia, Kyoto University was founded in 1897 and is responsible for producing many Nobel Laureates and winners of other prestigious international awards. The broad curriculum across the arts and sciences at both the undergraduate and graduate levels is complemented by numerous research centers, facilities, and offices throughout Japan and the world. For more information, please see: http://www.kyoto-u.ac.jp/en

magazine

Earth sciences and planetary messages

research method

Pilot study

Research topic

do not apply

Article title

Three-dimensional stress state above and below a plate boundary fault after the 2011 Mw 9.0 Tohoku earthquake

The date the article was published

November 9, 2022

COI statement

The authors declare that they have no known competing interests.

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