Japan braces for major quake amid moderate tremors ahead of 2011 Tohoku earthquake, Fukushima disaster anniversary

The warning comes after the January 1 earthquake in northern Japan, the most destructive in Japan since March 2011, that killed 250 people and caused the Fukushima nuclear disaster

28 quakes have been recorded since the start of March, with 30 similar tremors last month, prompting researchers to warn of a more catastrophic quake

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A man strolls on a beach surrounded by rubble in Minamisanriku, Miyagi prefecture on March 9, 2014, two days before the third anniversary of March 11, 2011 earthquake and tsunami. Photo: AFP

Published: 4:00pm, 9 Mar 2024Updated: 4:24pm, 9 Mar 2024

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.

“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.

Tsunami and earthquake damage is seen from a helicopter in the air of Sendai, Japan on March 12, 2011. Photo: US Navy

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.