The Japan Meteorological Agency issued an earthquake warning off the coast of Sanriku, Hokkaido, at 2:00 a.m. today, Tuesday, the 9th.
While the probability of a subsequent earthquake is low, it is recommended to exercise greater caution than usual for the next week or so due to the possibility of a major earthquake, and to make thorough preparations.
At approximately 11:15 p.m. yesterday (the 8th), a moment magnitude (Mw) earthquake struck off the east coast of Aomori Prefecture.
As a result of this earthquake, the probability of a subsequent major earthquake is considered relatively higher than usual in the area where a megathrust earthquake is expected, which extends from the coast of Nemuro, Hokkaido, to the coast of Sanriku, Tohoku. Please take disaster prevention measures in accordance with future announcements from the government and local authorities.
At approximately 11:15 p.m. yesterday (the 8th), a magnitude 7.5 earthquake struck off the east coast of Aomori Prefecture.
A detailed analysis of the epicenter and magnitude of the earthquake revealed that it was a moment magnitude (Mw) earthquake of 7.4, occurring in an area affecting the hypocenter of a major earthquake along the Japan Trench and the Kuril Trench. This earthquake met the criteria for issuing a post-earthquake information alert, as stipulated in the “Basic Plan for Promoting Disaster Prevention Measures for Trench-Type Earthquakes in the Areas Near the Japan Trench and the Kuril Trench.” As a result of this earthquake, the hypocenter of a major earthquake, extending from the coast of Nemuro, Hokkaido, to the coast of Sanriku, Tohoku, is believed to have a relatively higher than usual probability of experiencing another major earthquake of magnitude Mw 8 or greater.
If a major earthquake accompanied by a tsunami of the highest magnitude is predicted in the future along the Japan Trench or the Kuril Trench, a large tsunami is expected to affect a wide area, including the Pacific coast, and a large tsunami is expected to affect areas centered on the Pacific coast, from Hokkaido to Chiba Prefecture, in particular. Strong aftershocks are also predicted over a wide area.
According to statistical data on major earthquakes worldwide, of the 1,477 earthquakes with a magnitude of 7.0 or higher that occurred during the last century (1904–2017), only 17 earthquakes with a magnitude of 8 or higher (7.8 or higher) occurred within 500 km of the original earthquake and within seven days, a frequency of approximately 1 in 100. This data includes one case in which a magnitude 7 earthquake occurred two days before the 2011 Tohoku earthquake in the Pacific Ocean (Mw 9.0). Given the
low probability of another large-scale earthquake, residents of these areas should confirm their earthquake preparedness. Furthermore, residents of areas where tsunami inundation is expected should be prepared to evacuate immediately if they feel tremors or a tsunami warning is issued. For detailed information on disaster prevention measures, follow the instructions of national and local governments.
The Japan Meteorological Agency (JMA) will continue to closely monitor seismic activity along the Japan Trench and the Kuril Trench and will release information as appropriate.
*Moment magnitude (Mw) is obtained by carefully examining the displacement scale of the fault that generated the earthquake and is different from the magnitude calculated from the maximum amplitude of the seismic wave immediately after the earthquake, which is used to issue tsunami warnings and other seismic information.
*This information indicates that the probability of a large-scale earthquake occurring is relatively higher than normal, and does not imply that it will occur with certainty at a specific time.
(Reference) Information on a delayed earthquake off the coast of Sanriku, Hokkaido
Numerous earthquakes of varying magnitudes, ranging from Mw 7 to 9, have occurred in the areas along the Japan Trench and the Kuril Trench. According to the Central Council for Disaster Prevention, tsunami deposit data from the Pacific coastal region, stretching from Hokkaido to Iwate Prefecture, show that the largest tsunamis in the past have occurred approximately every 300 to 400 years. Considering the time elapsed since the 17th-century tsunami, the region is in a situation where a major earthquake followed by a tsunami is imminent.
