Researchers have raised the alarm about potential for a magnitude 9.3 mega-quake as pressure builds along the Chishima Trench off Hokkaido, according to multiple media reports.
Unreleased stress energy along the ocean trench has become large enough to potentially trigger what is known as a megathrust earthquake – a magnitude 9.0 or higher earthquake occurring at the convergence of two or more tectonic plates.
Researchers from the Agency for Marine-Earth Science and Technology and scientists from Tohoku and Hokkaido universities installed GPS observation stations on the seabed off Japan in 2018 to monitor plate movements. Each station was placed at a convergence point when an ocean plate sinks beneath a continental plate. Stations on both plates have moved around 8 centimetres per year in the same direction, toward Japan, indicating that the plates are solidly joined and massive stress may be accumulating.
The warning comes as Japan marks the 14th anniversary of the 2011 Tohoku earthquake and tsunami, a magnitude 9.0 disaster that killed around 16,000 people. Tomita Fumiaki, an assistant professor at Tohoku University International Research Institute of Disaster Science, fears that memories of the devastating event are fading, leading to less vigilance among the public. “We need to think again about what we can do to prepare for another megaquake,” he told NHK.
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Researchers estimate the chance of an earthquake with a magnitude of 8.8 or higher occurring near the Chishima Trench in the next 30 years could be as high as 40 percent. If a 9.3-magnitude earthquake hits that area, government projections from 2022 estimate it would cause 100,000 deaths.
The Tohoku earthquake originated from a rupture in a segment of the Japan Trench subduction zone, where the Pacific Plate thrusts beneath the Eurasian plate. At a magnitude of 9.0, it was the fourth-most powerful earthquake ever recorded globally and the strongest to strike Japan since the invention of modern seismology. Although 15,899 people died in the quake, with another 2,526 reported as missing and presumed dead, government estimates for a similar quake happening under the worst possible conditions are much higher.
A 2022 report estimates that a magnitude 9.1 earthquake in the Japan Trench could kill up to 199,000 people if it occurred late at night in winter. The 2011 quake, conversely, struck in the middle of the day in March, causing far fewer deaths despite being an only slightly weaker magnitude.
The government installed a new alert system in 2022 in seven coastal prefectures, including Hokkaido. The system is designed to encourage evacuation preparedness, as major earthquakes are often preceded by less severe quakes in the same vicinity that could give early warning – like the magnitude 7.3 quake that struck two days before the 2011 Tohoku earthquake.
