The government's Earthquake Research Committee analyzed the seismic activity off the coast of Tohoku for 10 years after the Great East Japan Earthquake, and evaluated that "a large-scale earthquake may occur over a long period of time, so caution is required." I summarized.
The government's Earthquake Research Committee met on the 9th to analyze the seismic activity of the 10 years from the occurrence of the great earthquake that caused the Great East Japan Earthquake to the beginning of this month.
According to this, the number of earthquakes of magnitude 4 or more that occurred in the aftershock area of the huge earthquake off the coast of Tohoku was 208 times for about one year from March last year, which is 25 minutes compared to the one year immediately after the earthquake. It means that it has decreased to 1 or less.
On the other hand, the number of earthquakes in the coastal areas of Tohoku and around the "Japan Trench" from Tohoku to the offshore of Kanto is higher than the average number of earthquakes before the earthquake.
In addition, GPS observations show that crustal movements that follow after the earthquake, so-called "aftereffect movements," are still being observed over a wide area of Tohoku and eastern Japan due to the effects of the huge earthquake.
Based on the above, the Earthquake Research Committee has summarized the evaluation that "a large-scale earthquake may continue to occur for a long period of time and may be hit by strong tremors and high tsunamis, so caution is required."
Naoshi Hirata, chairman of the Earthquake Research Committee and a member of the National Research Institute for Earth Science and Disaster Prevention, said, "In the north, south, and offshore areas of the epicenter of a huge earthquake off the coast of Tohoku, large earthquakes will continue to occur, causing strong shaking and high tsunamis. There is a possibility that a big earthquake will come. The big earthquake is not limited to Tohoku, and I want you to be prepared, thinking that it is inevitable as long as you live in Japan. "
Crustal movements after a huge earthquake The origin of Japan shifts
After the huge earthquake 10 years ago that caused the Great East Japan Earthquake, crustal movements such as ground stretch, subsidence and uplift have been observed in Tohoku and eastern Japan.
In the huge earthquake 10 years ago, Tohoku and Kanto moved to the east, and the Oshika Peninsula in Miyagi Prefecture moved up to 5 meters and 40 centimeters.
The "Japan Geodetic Origin" in Minato-ku, Tokyo, which was the standard for Japanese surveying, also moved 27 cm east.
"Aftereffect fluctuation" still
Since then, crustal movements and "aftereffect movements" that have continued due to the effects of the earthquake have been observed in various places.
From the day after the earthquake to last month, it has moved up to 1 meter 53 cm east in Kamaishi City, Iwate Prefecture, and up to 1 meter 49 cm east in Yamada Town, Iwate Prefecture and Kesennuma City, Miyagi Prefecture.
The movement is slower than immediately after the earthquake, but even in the last year, it has moved up to 5 cm to the east in Ofunato City, Rikuzentakata City, and Kesennuma City, Miyagi Prefecture.
Changes from subsidence to uplift along the Tohoku coast
Immediately after the earthquake, the ground subsided mainly along the coast of Tohoku, and on the Oshika Peninsula in Miyagi Prefecture, it subsided 1 meter and 7 centimeters. It is sinking.