Dec 8 Japan earthquake: Experts on alert for bigger ‘follow-up’ quakes
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A vehicle seen on a collapsed road in Tohoku town in Aomori prefecture on Dec 9, 2025, following a 7.5-magnitude earthquake off northern Japan.
PHOTO: AFP/JIJI PRESS
TOKYO – The powerful earthquake that struck late on Dec 8, with its epicentre off the east coast of Aomori prefecture, occurred in an area that has been hit by quakes in the past measuring 7 magnitude to 8 magnitude.
Its hypocentre was located within an area that is the presumed focal region of a quake predicted to happen along the Japan Trench or Chishima Trench, and which could result in at least 100,000 deaths.
The Japanese government is on the alert because a larger follow-up earthquake to the Dec 8 one may happen in that area.
The Dec 8 earthquake occurred north of the epicentre of the 9-magnitude Great East Japan earthquake that struck in 2011.
Like the March 2011 quake, the one on Dec 8 was a trench-type quake taking place at the boundary between the Pacific Plate on the sea side and the North American Plate on the land side.
It occurred as the Pacific Plate subducted – slid beneath – the North American Plate.
Major earthquakes, including the 8-magnitude Tokachi-oki earthquake in 2003 and the 7.6-magnitude Sanriku-Haruka-oki quake in 1994, occurred in the area and its surroundings.
Since the Dec 8 tremor occurred in a “void” with few recorded earthquakes of comparable magnitude, some experts suggest it may have taken place after part of a plate boundary, which had not entirely broken, was ruptured.
The government’s Earthquake Research Committee has estimated that earthquakes of about 7.9 magnitude could occur in the area once every 97 years.
According to the long-term assessment, earthquakes of 7 magnitude to 7.5 magnitude – similar to the Dec 8 tremor – could occur once every 8.8 years, and there is an “at least 90 per cent probability” of an occurrence within the next 30 years.
“It is possible that the plate boundary deep underground, which had not moved, largely shifted,” said Tohoku University’s Professor Shinji Toda, a seismology and geology specialist.
“We need to be vigilant for larger follow-up quakes.” THE JAPAN NEWS/ASIA NEWS NETWORK
