A huge earthquake 11 years ago could accelerate the occurrence of repeated large earthquakes in the past.
Experts repeated simulations of the magnitude 7 class "Miyagiken-oki Earthquake," which is said to have an average interval of 38 years, and in most cases, the interval between occurrences became shorter after the great earthquake.
Experts say, "Since a huge earthquake has occurred, I don't think there will be a big earthquake for a while, and I want you to be prepared for shaking."
Off the coast of Miyagi Prefecture, a magnitude 7 class "Miyagi Prefecture Offshore Earthquake" occurred repeatedly, and in 1978 (Showa 53), a block wall collapsed and 28 people were killed.
A research group of Assistant Professor Reiko Nakata of Tohoku University reproduced the shape of the plate around Tohoku in detail with a supercomputer, and simulated how the interval between occurrences of the Miyagiken-oki earthquake changes before and after a magnitude 9 class earthquake. ..
When the state of the plate boundary was changed little by little and a total of 251 cases were repeated, 90% of the cases were 232 cases, and after the huge earthquake, the interval until the Miyagiken-oki earthquake occurred was shorter than before. am.
On average, the interval between occurrences was about half.
The country's 38-year interval is not simply halved, but it is more likely that it will occur at shorter intervals.
Regarding the cause, the plate on the land side that jumped up during the huge earthquake continues to move in the same direction after the earthquake, and due to the effect of "aftereffect fluctuation", in the epicenter area of the Miyagiken-oki earthquake, it is between the plate on the sea side. I think that the fact that strain easily accumulates has an effect.
Assistant Professor Nakata said, "The Miyagiken-oki earthquake is smaller than the huge earthquake 11 years ago, but the epicenter is closer to the land, and the tremors can be experienced in a similar situation. In Tohoku, there are many. I think people know it, but don't forget to prepare for such a place. "
Periodic "Miyagiken-oki Earthquake"
Large magnitude 7 class earthquakes occur periodically off the coast of Tohoku, and in particular, the "Miyagi Prefecture Offshore Earthquake" that occurs off the coast of Miyagi Prefecture has been called for caution even before the Great East Japan Earthquake.
It was repeated in 1897, 1930s, and 1978, and especially in 1978, an earthquake of magnitude 7.4 occurred, observing violent shaking mainly in Sendai city, and 28 people were killed, such as the collapse of the block wall. rice field.
In addition, the residential land created by the embankment collapsed, causing great damage.
After that, in 2005, there was a magnitude 7.2 earthquake off the coast of Miyagi prefecture, and in the huge earthquake 11 years ago, the hypocenter area of the Miyagi prefecture offshore earthquake also moved.
Probability of occurring within 30 years 70-80% "More likely"
The National Headquarters for Earthquake Research Promotion has assumed that the average interval of occurrence of the Miyagiken-oki earthquake is 38 years based on the activities since 1897, and based on the number of years since the huge earthquake 11 years ago. We have announced that the probability of this happening within the next 30 years is 70% to 80%.
On the other hand, because of the research results like this one, "the probability may be even higher".
Even with the current numbers, the probability is still high, and it is important to take measures against shaking on the premise that it can happen at any time.