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Deepest scientific ocean drilling sheds light on Japan’s next great earthquake

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The deepest scientific drilling in the ocean sheds light on the upcoming Great Japan Earthquake

The deep-sea scientific drilling ship Chikyu, which in 2018 conducted the deepest drilling of an earthquake fault in the subduction zone. Credit: Satoshi Kaya / Flickr

Scientists who have delved deeper into an undersea earthquake fault than ever before have found that tectonic stress in Japan’s Nankai subduction zone is lower than expected, according to a study by researchers at the University of Texas at Austin and the University of Washington.

The results are published in the journal geologyis a mystery because the fault produces a major earthquake approximately every century and was thought to originate from another major earthquake.

“This is the core of the subduction zone, right above where the fault was locked, where the expectation was that the system should store energy between earthquakes,” said Damien Safire, director of the University of Texas Geophysics Institute (UTIG). He co-led the research and scientific mission that dug the bug. “It changes the way we think about stress in these systems.”

Although the Nankai Fault has been stuck for decades, the study shows that it has yet to show major signs of pent-up tectonic stress. According to Sfeir, this does not change the long-term view of the fault, which last erupted in 1946 – when it caused a tsunami that killed thousands – and is expected to happen again within the next 50 years.

Instead, the findings will help scientists learn about the link between tectonic forces and the earthquake cycle, and potentially lead to better earthquake predictions, both at Nankai and other faults such as Cascadia in the Pacific Northwest.

The deepest scientific drilling in the ocean sheds light on the upcoming Great Japan Earthquake

Harold Tobin of the University of Washington inspects drilling rigs. Researchers used similar equipment during a record attempt to drill the Japanese Nanki Fault in 2018 that was co-led by the University of Texas Institute of Geophysics. Credit: Harold Tobin/University of Washington

“Right now, we have no way of knowing if the big Cascadia earthquake – a magnitude 9 earthquake and tsunami – will happen this afternoon or 200 years from now,” said Harold Tobin, a researcher at the University of Washington. The paper’s first author. “But I have some optimism that with more and more direct observations like this, we can begin to recognize when something abnormal has occurred and that the risk of an earthquake is increasing in a way that can help people prepare.”

Giant confidence faults like Nankai and the tsunamis they generate are among the world’s most powerful and damaging, but scientists say they currently have no reliable way of knowing when and where the next major storm will strike.

The hope is that by directly measuring the perceptible force between tectonic plates pushing each other – tectonic stress – scientists can tell when a great earthquake is ready to strike.

However, their tectonic nature means that large earthquake faults are found deep in the ocean, miles below the sea floor, which makes measuring them directly very difficult. The excavation expedition Saver and Tobin are the earliest scholars to have come.

  • The deepest scientific drilling in the ocean sheds light on the upcoming Great Japan Earthquake

    Demian Safire, director of the University of Texas Geophysics Institute (UTIG), during scientific drilling of the ocean in Japan’s Nankai earthquake fault. Credit: Demian Safire/The University of Texas Geophysical Institute

  • The deepest scientific drilling in the ocean sheds light on the upcoming Great Japan Earthquake

    A drilling tool aboard the Chikyu science drill ship. Dozens of risers were joined together to reach deeper into the earthquake fault than ever before. Led by researchers at the University of Texas Institute of Geophysics and the University of Washington, the scientific expedition revealed that tectonic stress in Japan’s Nankai region was lower than expected. Credit: Demian Safire/The University of Texas Geophysical Institute

Their record-breaking attempt took place in 2018 aboard a Japanese scientific drillship, the Chikyu, which drilled two miles into the tectonic plate before the well became too unstable to continue, a mile from error.

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Nevertheless, researchers have collected invaluable data about subsurface conditions near the fault, including stress. To do this, they measured how much the shape of the well changed when the earth pressed against it from the sides, then pumped out water to see what it took to force its walls back down. This told them about the direction and strength of the horizontal pressure felt by the plate pressing on the fault.

Contrary to expectations, the expected horizontal stress created since the last great earthquake was close to zero, as if it had already released its pent-up energy.

The researchers suggested several explanations: It could be that the fault simply needed less pent-up energy than was thought to slip in a major earthquake, or that stresses lie closer to the fault than the craters have reached. Or a tectonic thrust could come on suddenly in the coming years. Either way, the researchers said, the drilling demonstrated the need for further investigation and long-term monitoring of the fault.


Can earthquake rates of magnitude 4 be used to predict large earthquake events?


more information:
Harold J. Tobin et al, Direct constraints on the in situ stress condition from deep drilling in the Nankai subduction zone, Japan, geology (2022). DOI: 10.1130 / G49639.1

Presented by the University of Texas at Austin

the quote: Deepest Ocean Scientific Drill Sheds Light on Upcoming Great Japan Earthquake (2022, September 22) Retrieved September 22, 2022 from

This document is subject to copyright. Notwithstanding any fair dealing for the purpose of private study or research, no part may be reproduced without written permission. The content is provided for informational purposes only.

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