The probability of a mega-earthquake after the Nankai-Tru quake is high: Japan research

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This September 2, 2019 file photo shows a coastal community in Kuroshio, Kochi Prefecture, an area expected to be hit by a tsunami following a possible earthquake in the Nankai Basin. Follow Favorite

TOKYO – If the massive Nankai-Tru earthquake, which is likely to strike somewhere in the Pacific Ocean outside areas of central to southwestern Japan, occurs in the near future, the probability of a resulting large earthquake is much higher than in normal times, According to a Japanese research team. and expect.

According to calculations by a team from Tohoku University, Kyoto University, and the University of Tokyo, the odds of a major tremor occurring within a week after the Nankai-Trog earthquake are 100 to 3,600 times greater than under normal conditions. The team says there has been no attempt to estimate the probability of major earthquakes occurring in a row, and notes that it’s important to be prepared for such a back-to-back occurrence. The study was published in the international academic journal Scientific Reports on January 10.

Along the Nankai Trough in the Pacific Ocean, stretching from Suruga Bay in central Japan to the Hyuga-nada Sea in the southwest, massive earthquakes have occurred repeatedly at intervals of 100 to 150 years. In recent history, the 1946 Nankai earthquake struck two years after the Tunankai earthquake – both in the same area in western Japan. Moreover, ancient records indicate that about 32 hours after the 1854 Tokai earthquake in central Japan, another large earthquake struck the Nankai region to the west, showing a tendency of cascading giant tremors with epicenters at various locations along the trough. Meanwhile, the epicenter of the 1707 Hui earthquake was not concentrated in one spot of the trough, but rather the entire basin became the epicenter.

In the latest research, Yu Fukushima, associate professor at the International Research Institute for Disaster Science at Tohoku University, and other scientists calculated the probability of consecutive earthquakes occurring at the Nankai Tru in the time since the initial quake, based on the incidence of consecutive massive earthquakes recorded in the International Earthquake Statistics and History of Nankai Earthquakes. Previous Trough dates from 1361 where the certainty of their occurrence was high.

The results showed that the probability of consecutive magnitude-8 plus giant earthquakes was 1-53% within six hours of the initial quake – 1,300 to 77,000 times higher than normal times. If in a week the probability was 2.1-77% – 100 to 3,600 times more likely than under normal circumstances – and 4.3-96% if in three years – 1.3 to 29 times higher than normal. The wide range of numbers shown in the results is due to the limited number of known earthquakes along the Nankai Basin, according to the team.

In the event that there is a high probability of a massive earthquake after an earthquake of magnitude 6.8 or greater in the expected Nankai Trough epicenter area, the Japan Meteorological Agency will urge caution by issuing special information on the Nankai Trough earthquake.

“The probability of consecutive earthquakes did not increase much over time, which indicates that the aftershocks were more likely to occur immediately after the (initial) earthquake,” Fukushima explained. He added, “This confirms the need to respond to private information, and it is important that we are prepared and trained on a daily basis so that we can respond quickly.”

(Japanese original by Yurika Tarumi, Science & Environment News Division)

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