The coast of the town of Erimo, Hokkaido, in the tsunami warning zone for earthquakes along the Japan and Chishima trenches is seen on April 30, 2025, in this photo taken from a Mainichi Shimbun aircraft. (Mainichi/Natsuki Nishi)
TOKYO — The northernmost prefecture of Hokkaido has seen a series of earthquakes registering 4 on Japan’s 7-point seismic intensity scale since mid-May. While the country’s weather body says these temblors are not large enough to trigger others, it is urging residents to regularly check their preparedness amid concern over a potential massive quake along the Chishima Trench off the prefecture’s coast.
According to the Japan Meteorological Agency (JMA), five earthquakes with a seismic intensity of 4 were recorded on the Pacific side of Hokkaido between May 15 and June 2. The magnitudes of these quakes ranged from 4.7 to 6.3. The areas these struck are known for frequent seismic activity.
Off eastern Hokkaido, the Pacific plate is constantly subducting beneath the continental plate. At the boundary of the two, there are areas where they are strongly attached, accumulating energy that could lead to a large quake. In 2003, the Tokachi-Oki earthquake, with a magnitude of 8.0, registered a maximum intensity of lower 6 on the 7-point scale.
Jumpei Shimizu, an inspector at the JMA’s Office of Large-scale Earthquake Analysis, noted about recent tremors, “The epicenters are distant from each other, making it unlikely they are related.” He added, “They are not of a scale that would induce other earthquakes, nor can they be considered a precursor to a major quake.”
However, along the Chishima Trench stretching from off the coast of the Tokachi region in southeast Hokkaido to the Chishima Islands, also called the Kuril Islands, a major earthquake apparently could occur at any time. The national government’s Earthquake Research Committee estimates a 7% to 40% chance of a magnitude 9-class quake occurring within the next 30 years. Shimizu emphasized, “It’s important to think about what actions to take when such an event happens.”
There are also concerns about a major earthquake along the Japan Trench, which stretches on the Pacific side from off the coast of Honshu’s Tohoku region to off Hidaka in southern Hokkaido. If a major quake occurs in the Japan Trench or Chishima Trench, it is anticipated that a tsunami could result in up to about 200,000 fatalities.
If an earthquake of magnitude 7 or greater occurs around the Japan Trench, the JMA will issue a “Hokkaido-Sanriku offshore subsequent earthquake advisory,” warning of the potential for an even larger subsequent tremor.
This advisory covers 182 municipalities across seven prefectures from Hokkaido to Chiba. While it does not call for preemptive evacuation, it advises residents to be vigilant for about a week. The government expected to issue this advisory about once every two years, but since its introduction in December 2022, it has not yet been issued.
(Japanese original by Kazuki Mogami, Tokyo City News Department)
AloJapan.com