Japan braces for major quake amid moderate tremors ahead of 2011 Tohoku earthquake, Fukushima disaster anniversary
Just days ahead of the anniversary of the March 2011 earthquake and tsunami that devastated swathes of northeast Japan, there is growing concern that a new series of moderate quakes off the east coast could be the precursor to another major quake.
The Jama Meteorological Agency (JMA) has recorded 28 quakes since the start of March this year, and 30 similar tremors last month. Most have been relatively small, but there were several level-four quakes on the agency's seven-level seismic intensity scale. A quake on February 29 had a magnitude of 4.9 and another the following day registered a magnitude of 5.2.
The quakes are occurring both onshore and off the coast, with the JMA warning that tectonic plates are experiencing a "slow-slip event" between the continental plate and the Philippine Sea plate to the east of Chiba Prefecture.
Do you have questions about the biggest topics and trends from around the world? Get the answers with SCMP Knowledge, our new platform of curated content with explainers, FAQs, analyses and infographics brought to you by our award-winning team.
"This area off Chiba Prefecture has seen this sort of slow-slip activity several times over the last few decades, with a series of small to medium-sized quakes coming and going over time," said Yoshiaki Hisada, a professor who specialises in the study of earthquakes at Japan's Kogakuin University.
"People sometimes think that these slow-slip quakes are safer because they are releasing smaller amounts of energy more often, but that is incorrect and the energy being released is much smaller than if there was a big quake," he told This Week in Asia.
An earthquake occurs when stresses on a fault line, or where tectonic plates meet, build up and rupture. That often results in a powerful shock as the plates slide past each other rapidly, although a slow-slip event will see frequent smaller tremors over an extended period. Experts warn, however, that it does not necessarily mean that the pressure on the plates is being eased completely and that a more catastrophic quake is still possible.
While the subterranean activity taking place off Chiba involves different tectonic plates from the faults that shifted so dramatically on March 11, 2011 - causing a magnitude-9 quake that immediately resulted in a tsunami that was in places almost 40 metres high - Hisada warns of more danger.
"Yes, it is a different fault, but this line is closer to the coast of Chiba Prefecture," he pointed out. "A tsunami may not be as big as the one that struck Tohoku, but it will hit the coast much faster and with less warning."
John Harris, a Canadian speech-writer, lives about 3km from the waterfront in the town of Onjuku and said people have become accustomed to the disruption to their lives amid frequent tremors.
"We experienced the big earthquake in 2011 here but were fortunate to escape the tsunami," Harris said. "The damage from that tsunami started about 70km north of Onjuku and destroyed towns and villages for hundreds of kilometres to the north.
"Unfortunately, 13 years later, this municipality does not seem to have done much to prepare for another disaster and there are serious bottlenecks on the routes leading away from the harbour if a tsunami is coming," he said. "That is a serious worry."
Some of Harris' neighbours have been taking more precautions in recent days, stocking up on supplies and buying generators, but he says there is no sense of panic.
"Everyone in Japan is very used to earthquakes, so they are just taking this all in their stride," he said. "The quakes wake me up, but what can you do about it?"
Kogakuin University's Hisada said the Japanese people were shocked by the images that emerged in the aftermath of the January 1 earthquake on the Noto Peninsula in northern Japan. The magnitude-7.5 tremor - after a swarm of dozens of smaller quakes in the weeks before - was the largest and most destructive in Japan since March 2011, releasing a 6.5-metre tsunami and causing 250 deaths.
"I believe people saw what happened there and have been making preparations since then," Hisada said. "The most important thing is to have a modern and strong home because we saw that many of the older, wooden buildings in Noto collapsed.
"It is clear that anyone who was trapped in a collapsed building and could not get out was not able to then escape from the tsunami or later froze to death."
This article originally appeared on the South China Morning Post (SCMP).
Copyright (c) 2024. South China Morning Post Publishers Ltd. All rights reserved.
