"Half crack" Nankai Trough mega earthquake Another worst assumption March 3 17:37
"The worst scenario may be 'half-broken,'"
earthquake experts said.
What is the "worst case scenario" of the Nankai Trough megathrust earthquake, which is said to occur in the near future?
This time, when I examined it from the three aspects of "earthquake shaking", "disaster relief", and "economy", I realized that most of us living in Japan are facing a situation that we cannot ignore. rice field.
(NHK Special "Nankai Trough Mega Earthquake" coverage team)
Nankai Trough "Seismic Intensity 7" Repeatedly
This map is a hypothetical seismic intensity distribution map of the NHK special drama "Nankai Trough Mega Earthquake" broadcast on March 4th.
A seismic intensity of 7 was recorded in Shikoku, Kinki, and Kyushu.
On the other hand, in Kanto and Shizuoka, the seismic intensity is 3 or 4.
In fact, it shows the assumed image of the "half split" of the west by the government in the Nankai Trough earthquake.
Its magnitude is 8.9.
But this earthquake is not the end.
In the Nankai Trough, if a mega-earthquake occurs only in the western region, the risk of mega-earthquakes in the eastern region also increases.
The seismic intensity distribution map of the assumed image of "half crack" in the east is below.
In Aichi, Shizuoka, and Mie, a seismic intensity of 7 was recorded.
The Kanto-Koshin and Kinki areas will also be hit by tremors with a seismic intensity of 6-upper or 6-lower.
Massive earthquakes hit the densely populated areas on the Pacific side, and they occur in rapid succession.
Authority on Disaster Prevention “On the Decline of Japan”
Two huge earthquakes that modern Japan has never experienced.
Professor Emeritus Yoshiaki Kawata of Kyoto University, who has been leading Japan's disaster prevention efforts for many years, points out that there is a risk that the disaster will become a "national disaster" that will affect Japan's national strength.
Yoshiaki Kawata, Professor Emeritus of Kyoto University
, "The damage is so great that it's a huge disaster that you don't know where to start. In this era, everything is connected to the network, so even a part of it can be greatly damaged. For example, if a huge earthquake hits Osaka and Nagoya, causing great damage, and Sapporo and Fukuoka are all okay, the damage will be unbelievable. In addition, it is conceivable that the decline of Japan will begin.”
What is Nankai Trough "Hanwari"?
So, what is this unfamiliar “half crack”?
When many people hear the Nankai Trough earthquake, they imagine a huge earthquake that hits the Pacific side at once.
At this time, the country assumes a worst-case death toll of 323,000.
This damage assumption is based on the assumption that the hypothetical focal area of the Nankai Trough shifts suddenly.
This case is also called a "complete crack" (*Seismologists sometimes use the term "crack" to describe the occurrence of an earthquake).
On the other hand, another case where the government and experts call for strong vigilance is ``half split''.
As shown in the figure above, for example, the eastern hypocentral region (red) and the western hypocentral region (yellow) move separately, with a gap in time between them.
This “half split” has happened repeatedly historically.
In 1854 during the Edo period, the Ansei Tokai Earthquake and the Ansei Nankai Earthquake occurred 32 hours apart. It's happening at different times of the year.
So what will happen in the two giant earthquakes?
We will look at the impact of (1) "double tremors," (2) "disaster relief," and (3) "the Japanese economy."
Impact (1) Buildings damaged by two severe earthquakes?
The first effect is the "double tremor".
In the 2016 Kumamoto earthquakes, buildings collapsed one after another in areas hit by seismic intensity 7 on two occasions.
Such damage can be widespread.
Further interviews with experts revealed that skyscrapers such as office buildings and tower apartments may suffer unprecedented damage.
Large cities such as Osaka, Nagoya, and Tokyo are expected to be particularly hard hit.
A skyscraper...
This time, with the cooperation of Project Professor Katsuhisa Nishimura of Setsunan University, who is familiar with the structural design of buildings, we simulated a case in which a skyscraper was hit by two quakes that "cracked in half".
The structure of a 25-story, 100-meter-tall steel-frame office building in Osaka with a vibration damping device is reproduced on a computer.
I entered twice the expected shaking on the ground in Konohana Ward, Osaka.
As a result, part of the building's steel frame turned red during the first tremor.
It shows that it has changed.
If the steel frame could not be repaired and a second tremor hit, there were areas that turned blue, especially in the lower floors.
This means that the deformed steel frame broke because it could not withstand the shaking.
This resulted in skyscrapers potentially taking damage that made them unusable over time.
Professor Nishimura, who conducted the analysis, said that the possibility of a skyscraper collapsing is low, and that two large tremors, such as those that hit Osaka in the Nankai Trough earthquake, are assumed according to current building design standards. Point out that it is not.
Professor Katsuhisa Nishimura of Setsunan University
``For example, even if you bend a wire with a twist, it will only deform if you bend it once or twice and it will not break. The current design standards for buildings do not assume that they will be attacked by two long-lasting tremors, so if a Nankai Trough earthquake occurs, there is such a risk. Structural designers, building owners, and us who use buildings need to understand.”
Influence (2) No help will come to the disaster area?
The second impact of "halving" is "delay in rescue to the disaster area".
Once a huge earthquake occurs, the possibility of the next huge earthquake increases, so there is a risk that rescue will be greatly delayed.
It was found that it was affected by the "Emergency Fire Relief Team".
This unit was created based on the lessons learned from the Great Hanshin-Awaji Earthquake of 1995.
However, it is said that it was decided in advance plans that the ground forces in one of these areas would not be able to be dispatched to the disaster area if the Nankai Trough was split in half.
What does that mean?
Prioritizing local activities
Units in 10 prefectures along the Pacific coast (Shizuoka, Aichi, Mie, Wakayama, Tokushima, Kagawa, Ehime, Kochi, Oita, and Miyazaki) do not plan to go to disaster areas in other prefectures.
The reason is to prepare for the second "half break".
This is because even if the damage caused by the first huge earthquake is small, another huge earthquake may occur while you are going to support the affected areas.
In other words, stay in your hometown in preparation for a second big earthquake.
Looking at the plan in detail, it is stipulated that within one week after the earthquake occurs, they will not go out to support and will be engaged in activities in their own prefecture (*excluding the air platoon).
Shozo Nagata, a professor at Kansai University who is familiar with firefighting administration, said that it was unavoidable considering the risk of being "halved", but pointed out that there was a risk that some areas would become "isolated" without rescue coming. .
Professor Shozo Nagata of Kansai University
"The impact of not being able to rush to the unit is not only personnel, but there is a possibility that special vehicles such as amphibious vehicles in preparation for tsunami disasters cannot be used. The disaster area has been isolated and training has been repeated. Residents, especially coastal municipalities, should recheck hazard maps and evacuation routes, and prepare for the possibility that rescue may not come.”
Impact (3) The damage to the Japanese economy is...
The third impact of the "half split" is serious damage to the Japanese economy.
Now, for the first time, experts have simulated the economic impact of two megaquakes.
The research group of Professor Hiroyasu Inoue of the University of Hyogo went there.
We assumed two occurrences of the Nankai Trough megathrust earthquake.
A "half crack" occurs in the west, and half a year later, a "half crack" occurs in the east.
Using the transaction data of more than 5 million companies nationwide and the damage assumption of the country, we simulated how much the production value of domestic companies will decline with the supercomputer "Fugaku".
10 times more damage than the Great East Japan Earthquake
This is the result of that simulation.
Blue shows the case where the "half crack" in the west occurred only once.
On the other hand, the orange shows the case where the eastern halves also occurred.
We can see that the production value of companies that had been recovering suddenly drops at the "half-break" in the west, and does not return to the original level.
Professor Inoue analyzes that the "supply chain" = "product supply network" of companies will be cut off, which will have a serious impact.
In simulations, the total amount of corporate production lost in the first year after the first earthquake hit 134 trillion yen.
It is 10 times the size of the Great East Japan Earthquake and is equivalent to Japan's national budget.
Professor Hiroyasu Inoue, University of Hyogo
: “Because all companies are connected by countless supply chains, once a big shock occurs, a chain reaction of bankruptcies will occur like a domino toppling. We have not fully recovered from that. By the way, if a second huge earthquake were to occur, the damage would be enormous, and the Japanese economy might not be able to fully recover.”
"My predecessors got over it"
As revealed in this interview, there is a risk unique to a "half crack" in which two huge earthquakes hit Japan.
I think it's a situation that makes you want to turn your eyes away.
On the other hand, many experts say, "We can reduce the damage if we take measures."
Of these, I would like to introduce the words of Professor Emeritus Nobuo Fukuwa of Nagoya University, who has been researching the Nankai Trough megathrust earthquake for many years.
Nobuo Fukuwa, professor emeritus at Nagoya University,
"Japan has experienced nine Nankai Trough earthquakes in its history, but our predecessors have overcome each of them. If we face earthquakes firmly, we will be able to overcome the next disaster and create a better era.Since we know that an earthquake is coming, we should not only be terrified, but overcome it positively. It is necessary for society to change in a tangible way.I hope that each and every one of us must be well prepared for an earthquake and continue to have the desire to reduce the damage.”
* Details of the assumptions and countermeasures introduced in this article are summarized on a special page for each theme.
Disaster Archipelago Life-saving information site
Knowing all about the "Nankai Trough Mega Earthquake"
It will also be featured in the NHK special "Nankai Trough Mega Earthquake" scheduled to be broadcast on March 4th and 5th.
NHK Special Nankai Trough Great Earthquake
Part 1 Drama (Part 1) Scheduled to be broadcast on Saturday, March 4 at 7:30 pm Scheduled to be distributed on NHK Plus
Reporter
Goichi Miyahara
Joined in 2008
After working at the Great East Japan Earthquake Secretariat and Tokushima Broadcasting Station, he is currently
in charge of covering disaster prevention such as the Nankai Trough earthquake.
News Reporter
Yuki Wakabayashi
Joined in 2012
First post
was in charge of the Kagoshima Bureau Metropolitan Police Department, and from 2020 in charge of disasters
Director of Social Program Department
Makoto Kanamori
Joined in 2006
After working at Tottori Broadcasting Station and Morioka Broadcasting Station, he is currently in
charge of news programs such as NHK Special and Close-up Gendai.
Project Center Director
Kentaro Miki Joined
the station in 2010
After working in the Science and Environment Program Department of the Osaka Station, he is currently in
charge of NHK specials such as the new coronavirus and global warming.