It has been 11 years since the Great East Japan Earthquake struck.
It is said that a huge earthquake and a big tsunami are imminent again on the coast from Hokkaido to Kanto including the disaster area.
In December of last year, serious damage estimates were announced in a part of the "Japan Trench" and the "Kuril Trench" off the coast of Hokkaido.
However, there is no way to know for sure when the next big earthquake will occur and how big it will be.
Therefore, researchers are paying attention to crustal movement data.
How do you know the "invisible enemy"?
What did you find out there?
Kuril / Japan Trench From the traces of the past, "Otsunami imminent"
Of the "Kuril Trench" and "Japan Trench" from the Kuril Islands to the offshore of Hokkaido, in the area from the south of Hokkaido to the offshore of Iwate Prefecture, the national government announced damage estimates for a magnitude 9 class earthquake in December last year. However, in the worst case, the death toll will reach 100,000 in the Kuril Trench and 199,000 in the Japan Trench.
Regarding these areas, the national government states that "a large tsunami is imminent", but this is about from the survey of "tsunami deposits" such as earth and sand carried by the tsunami, in all areas from the previous huge earthquake. This is because it is thought that it has been about 400 years.
So to speak, it is based on historical data.
Search for "strain" from crustal movements
At present, there is no way to know for sure when the next big earthquake will occur and how large it will be.
Under these circumstances, the research group of Associate Professor Takuya Nishimura of the Kyoto University Disaster Prevention Research Institute is trying to grasp the situation of the plate from the data of crustal movement.
We use GPS data installed on land.
A large earthquake occurs when the strain builds up at the boundary between the subducting sea-side plate and the land-side plate and reaches the limit.
The amount of strain that accumulates depends on how tightly the plates are attached to each other = "sticking".
If the plate boundaries are not too sticky, they will slip.
On the other hand, if it is firmly attached (= fixed), the plate on the land side will move together, so the GPS observation point on land will move very slightly.
Based on this data, the strength of sticking of the plate far away can be grasped.
As a result of calculation based on the latest knowledge such as the shape of the plate and the movement of the mantle that moves the plate, the color is darker from the northern part of Iwate prefecture to the eastern part of Aomori prefecture along the Chishima Trench, off Nemuro and Tokachi, and along the Japan Trench. It shows that the sticking is strong.
It seems that the strain continues to accumulate up to about 8 cm per year.
You might think, "8 centimeters a year?", But it's 8 meters in 100 years and 40 meters in 500 years.
If it shifts all at once, it may lead to a big tsunami.
Associate Professor Nishimura says, "Strains are steadily accumulating where the strains have not been released due to the Great East Japan Earthquake. We must be vigilant against earthquakes and tsunamis."
Observation using the power of waves
On the other hand, the crustal movement caused by the magnitude 9 earthquake is still continuing, and it is difficult to grasp the state of the plate boundary.
For this reason, the GPS data used by Associate Professor Nishimura's group is limited to before the great earthquake, and there is a problem that the latest data cannot be used.
Under these circumstances, JAMSTEC = Japan Agency for Marine-Earth Science and Technology and Tohoku University are increasing the number of observation devices to directly grasp the crustal movement of the seafloor where the plate is subducting.
The challenge was to have to go to the observation point by ship in order to collect data, but it is expected that the new device "Wave Glider" will help overcome this.
Since it can proceed using the power of waves, it is possible to navigate unmanned for a long time while acquiring data from multiple observation points.
"Strain" that continues to accumulate even after a huge earthquake
The latest data is currently in the process of analysis, but it was found that the observation point about 200 km off the coast of Aomori Prefecture moved west by an average of 3 cm in the 10 years from the year after the great earthquake to last year. am.
The research group believes that the strain continues to accumulate even after the great earthquake, and will investigate it in more detail.
Takushi Iinuma, Group Leader of JAMSTEC, said, "By improving the accuracy of seafloor observations, it will be possible to quantitatively know how much strain is accumulated and how much earthquake will occur when it is released. It will be used for future risk assessment. I want to repeat observations so that I can do it. "
Measures can significantly reduce damage ・ Take measures without pessimism
While it is said that the largest tsunami is imminent in the Chishima Trench and the Japan Trench, the number of victims will be reduced by about 80% if evacuation is started in about 10 minutes from the earthquake while securing evacuation destinations. It is estimated that it can be done.
Please think about which evacuation destination is best for you and your family, and reconfirm what kind of risks you have around you.