The "Hokkaido-Sanriku Offshore Subsequent Earthquake Warning Information" is announced as the possibility of a huge earthquake in the "Kurishima Trench" and "Japan Trench" has increased.
What kind of information?
When will it be announced?
What should I do?
Summarized in a Q&A format.
Q. What kind of information is it?
A. It is information that the possibility of a huge earthquake occurring is higher than usual, so please be careful of earthquake tremors and tsunamis.
The government assumes that the Kuril Trench and the Japan Trench (north of the area where the Great East Japan Earthquake occurred), which are located offshore from Hokkaido to Iwate Prefecture, will each have a magnitude 9-class earthquake.
The Japan Meteorological Agency has announced that there is a relatively high probability of a large earthquake (early earthquake) occurring, followed by a larger earthquake (later earthquake).
Q. What is a giant earthquake in the Chishima Trench and Japan Trench?
A. It is the boundary where the plate on the ocean side is subducting on the land side from Hokkaido to the coast of Boso.
The Chishima Trench extends from the coast of Etorofu Island in Hokkaido to the coast of Tokachi, and the Japan Trench extends from the east coast of Aomori Prefecture to the coast of Boso in Chiba Prefecture, where seismic activity is active.
According to the government's Earthquake Research Committee, huge earthquakes accompanied by magnitude 8 class tsunamis, such as the 1952 Tokachi-oki earthquake, have occurred in the Kuril Trench.
A survey of tsunami deposits suggests that in the 17th century, a huge earthquake occurred that caused the entire area to shift at once, and that a high tsunami like the Great East Japan Earthquake surged.
Along the Japan Trench, earthquakes of magnitude 7 class have occurred repeatedly, and in 2011, a huge earthquake of magnitude 9.0, which caused the Great East Japan Earthquake, occurred.
It is believed that large earthquakes occurred in these regions at intervals of 300 to 400 years, and the government's Earthquake Research Committee said, "There is a high possibility that a large earthquake that will cause a large tsunami is imminent." increase.
Q. What kind of damage will a huge earthquake cause?
A. A maximum of 100,000 to 190,000 people are expected to die, and 220,000 buildings are expected to be completely destroyed.
According to the assumption announced by the government in 2021, if a huge earthquake occurs in the "Kurishima Trench" or "Japan Trench", a huge tsunami exceeding 20 meters at maximum will hit the coast of Hokkaido and northern Tohoku, and the maximum number of deaths will be 190,000. It is estimated that it will cause serious damage that reaches humans.
In addition, it is expected that up to 220,000 buildings will be completely destroyed, and port facilities will also be severely damaged.
In addition, "hypothermia" peculiar to cold regions is also a big problem.
It is assumed that in the event of an earthquake in the harsh winter, there are 42,000 people in the Japan Trench who are at risk of being caught in the tsunami or spending long periods of time outdoors. It is estimated that 22,000 people will reach the Kuril Trench.
Q. Why did you decide to release the information about the huge earthquake warning?
A. It is known that even larger earthquakes have occurred in and around the focal region after a large earthquake, so if by any chance a large earthquake occurs, the damage will be reduced as much as possible.
In the "Japan Trench" and "Kurishima Trench", there are cases where huge earthquakes of magnitude 7 and 8 or 9 have occurred.
The most recent is the 9.0 magnitude earthquake on March 11, 2011, which triggered the Great East Japan Earthquake.
There was an earthquake of magnitude 7.3 two days ago.
In 1963, there was a magnitude 7.0 earthquake with its epicenter off the southeast coast of Etorofu Island, followed 18 hours later by a magnitude 8.5 earthquake.
Therefore, the Japan Meteorological Agency (JMA) held a joint press conference with the Cabinet Office about two hours after the occurrence of the first earthquake, stating that the probability of a large earthquake occurring after a magnitude 7 class earthquake is increasing. will be announced.
The target area is 182 municipalities in Hokkaido, Aomori, Iwate, Miyagi, Fukushima, Ibaraki, and Chiba prefectures, mainly on the Pacific Ocean side.
Q. What should I do if I receive information?
A. Life and economic activities are normal.
But you need to double check your preparedness just in case.
Even if the information is issued, it does not mean that a later earthquake will occur, and there is no call for evacuation in advance.
If the information is announced, it is required to maintain daily life for about a week, and to be prepared to act immediately if prompt evacuation is necessary, such as when a tsunami is expected.
Regarding specific measures, the government has detailed guidelines.
Q. How accurate is the information?
A. About 1/100 will lead to a huge earthquake.
The government has stated that "even if information is issued, it does not necessarily mean that a huge earthquake will occur."
On the other hand, the announcement of information will be more frequent, about once every two years.
According to global statistics, a magnitude 7 class earthquake is followed by a magnitude 8 class earthquake in about 1 out of 100 times, and a 9 class earthquake is even lower.
On the other hand, according to the government's explanation so far, based on the history of past earthquakes, late earthquake warning information is expected to be announced frequently, about once every two years.
A report by a study group of national experts also said, "There is a high possibility that the information will be false."
A huge earthquake accompanied by a tsunami may occur suddenly before any information is issued, or a large-scale earthquake may occur one week after the initial earthquake, so it is important to always be prepared.
Q. How should we receive “information”?
A. Think of it as a “practice swing” rather than a “missing swing” and prepare accordingly.
We interviewed Specially Appointed Professor Toshitaka Katada of the Graduate School of the University of Tokyo, who served as the chairman of the investigative panel of national experts.
Mr. Katada points out that when information is released, there is no guarantee that a huge earthquake will occur afterward, but it should be understood that the probability is relatively higher than usual.
"Basically, I would like you to understand that it is impossible to predict or forecast earthquakes. This information is only for the event that an earthquake of magnitude 7 class occurs, an earthquake linked to it will occur, and a tsunami will occur. "
It's true that it's very uncertain information, but if you think 'Nothing happened' or 'I lost money by running away'. , The information itself becomes a “wolf boy”, and when the time comes, you will be in a situation where you should have escaped.Therefore, I want you to take it as a “practice” rather than a “fake”.Protect yourself and your family. I want you to think of it as information for your own sake, and use it proactively and wisely.”
Q. What is the difference from "Nankai Trough Earthquake Temporary Information"?
A. It is the same as information calling for preparations for subsequent earthquakes.
Calls to evacuate in advance are very different.
In the same way, there is "Nankai Trough Earthquake Temporary Information" as information that calls for disaster prevention measures for subsequent earthquakes.
There are two major differences from the "Hokkaido/Sanriku Offshore Subsequent Earthquake Warning Information".
If an earthquake with a magnitude of 6.8 or higher occurs in or around the hypothetical focal region, or abnormal crustal movements are observed by strain gauges, the "Nankai Trough Earthquake Extraordinary Information" will be used to investigate the relationship with a huge earthquake. Information is issued with the keyword "under investigation", which indicates that the issue has been resolved, and an "evaluation committee" made up of experts conducts examinations.
On the other hand, in the Kuril Trench and Japan Trench, which are subject to "subsequent earthquake warning information", scientific observation results and knowledge are not sufficient, and the mechanism of past mega-earthquakes is not well understood. No expert review will be performed.
Another point is the call for "advance evacuation".
In the Nankai Trough Earthquake Temporary Information, when an earthquake of magnitude 8 or more occurs at the plate boundary, temporary information is announced with the keyword "major earthquake warning", and residents in areas where evacuation cannot be done in time for the tsunami to reach 1 Continued evacuation is called for for the week.
On the other hand, since knowledge of the Japan Trench and the Chishima Trench is limited, there is no call for advance evacuation in the "Late Earthquake Warning Information".
Q. What are your future challenges?
A. Continuing awareness among residents and concrete measures.
Regarding information, the government clearly points out that "even if the possibility of a large-scale earthquake occurring is relatively higher than usual, there are more cases where subsequent earthquakes do not occur."
It is important for those who use these characteristics (residents, companies, regions, etc.) to understand them well and to take concrete countermeasures.
On the other hand, the difficulty of promoting public awareness and understanding has also become clear in the "Nankai Trough Earthquake Extraordinary Information" that the government has already begun to operate, and according to a questionnaire conducted by NHK in the target area, it has not progressed to permeate the residents. Nearly 80% of municipalities responded.
In order to advance preparations while gaining the understanding of residents, the national and local governments need to work together to repeatedly raise awareness and continue to take concrete measures.