"Slow slip" confirmed for the first time on the sea floor offshore To elucidate the earthquake mechanism January 16, 5:30
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A major earthquake in the Nankai Trough is likely to occur. For the first time, the University of Tokyo and the Japan Coast Guard have observed a phenomenon called “slow slip” in which the plate boundary moves slowly on the seabed far away from the land of Shikoku from the Tokai. It is a phenomenon that has been attracting attention for its relation to a huge earthquake, and is expected to lead to elucidation of the mechanism and disaster prevention measures.
This time, "slow slip" was confirmed at seven locations, including off Bungo Suido and off Kii Suido, all of which are more than 50 km away from land.
The Japan Coast Guard has installed equipment capable of observing ground movement in the hypocenter area assumed in the Nankai Trough and about 15 places on the sea floor south of it. It was confirmed in seven places by the year.
At two locations off the Kii Suido, around 2018, they moved 6 cm and 8 cm in the southeast direction, respectively.
“Slow slip,” in which the boundaries of the plate move slowly, is a phenomenon that has been noticed as if the change in movement was related to a huge earthquake in the Nankai Trough.
This is the first time it has actually been caught on the ocean floor far from land, and it is hoped that this will lead to elucidation of the mechanism and disaster prevention measures.
"I would like to collect further observation data to understand what is happening at the plate boundary and use it for simulation research to lead to disaster prevention," said Japan Coast Guard's Naoshi Ishikawa, volcano investigator.
What is "slow slip"?
"Slow slip" is a phenomenon in which the boundary between plates moves slowly without causing the shaking that you feel on your body.
Off the east coast of Chiba Prefecture, where the plate of the Japan Trench is located, it is known that "slow slips" occur every few years, after which relatively large earthquakes are more likely to occur.
On the other hand, "slow slips" have been repeatedly observed from the Tokai to Shikoku, mainly on the land side, where the plate boundary of the "Nankai Trough" is located, but the relationship with large earthquakes is clear. not.
The first thing that was confirmed this time was a "slow slip" that occurred at the boundary of the shallow part of the plate more than 50 km from the land to the sea side, and future research on the relevance to the earthquake will attract attention.