As Japan marks 13 years since 2011 earthquake & tsunami, experts warn of another megaquake

Japan is marking the 13th anniversary of the 2011 earthquake and tsunami, which also sparked off the tragic Fukushima nuclear disaster.

The country is still emerging from the shadow of this traumatic experience that led to massive loss of life and property, and left many with nothing to their name.

But now, there are fears of a similar tragedy happening again. Experts warn that seismic conditions in an underwater trench off Hokkaido indicate the potential for another massive earthquake.

A five-year study of the Chishima Trench, about 150 kilometers (93 miles) offshore, found that tectonic plates beneath the trench are not slipping past each other but appear to be locked together. Researchers say that when the plates eventually break free, they could unleash a devastating earthquake, according to a report by South China Morning Post.

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Scientists from the Japan Agency for Marine-Earth Science and Technology, Tohoku University, and Hokkaido University believe the plates have remained fused since the last major earthquake in the region in the 17th century.

A separate government report estimated that a magnitude-8.8 quake in the trench within the next 30 years has a probability between seven and 40 per cent.

SCMP cited Fumiaki Tomita, assistant professor at Tohoku University’s Research Center for the Prediction of Earthquakes and Volcanic Eruptions, as saying that predicting seismic activity is notoriously difficult.

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“Our task was to observe the current situation of the sea floor displacement off Hokkaido, but that does not allow us to discuss the possibility of an earthquake in the future.”

Concerns over another megaquake

Researchers installed GPS observation equipment on the seabed in 2019 and found that instead of moving gradually, the plates appear to be stuck together. If they slip suddenly, Tomita said the energy released could be equivalent to a magnitude-8.8 earthquake.

Japan’s last megaquake, the March 11, 2011, Great East Japan Earthquake, was a magnitude-9.0 event that struck 72 kilometers (45 miles) east of Miyagi prefecture. It remains the strongest earthquake ever recorded in Japan and the fourth most powerful globally since 1900.

The quake triggered a massive tsunami, with waves reaching more than 40 meters (131 feet) high and traveling inland as far as 10 kilometers (6 miles). The disaster killed 19,759 people, with 2,553 still listed as missing, and caused a meltdown at the Fukushima nuclear power plant , the worst nuclear disaster since Chernobyl.

READ MORE: Fukushima disaster: UN nuclear chief to visit contaminated soil storage

Potential impact of a Chishima Trench earthquake

A magnitude-9.3 earthquake in the Chishima Trench or the nearby Japan Trench could cause 199,000 deaths, displace more than 500,000 people, and destroy 220,000 buildings, according to government estimates. Economic damage would total about ¥31.3 trillion ($211.5 billion).

While those figures represent a worst-case scenario, even smaller earthquakes could cause widespread devastation, said Yoshiaki Hisada, a professor at Kogakuin University in Tokyo who studies the impact of earthquakes on buildings.

“The biggest danger is the tsunami that comes with an offshore quake and while the likelihood of another magnitude-9 quake, like we saw in Tohoku in 2011, is quite low, there is a far greater possibility of magnitude-7 or -8 quakes,” Hisada said.

Tsunami waves from a quake of that size could reach between 10 and 20 meters (33 to 66 feet) high, depending on seabed conditions, coastal geography, and other factors, he said.