The Kanto region is shaking eerily.
On the morning of October 28, an earthquake of intensity 4 occurred in southern Ibaraki Prefecture, and on the night of October 7, an earthquake of intensity 5 or higher occurred in northwestern Chiba Prefecture, and an earthquake of intensity 5 or higher was observed in the capital city of Tokyo, temporarily halting the transportation infrastructure.
Please see the map below.
From January to November 1 this year, a total of 31 strong earthquakes of intensity 4 or higher occurred mainly on the Pacific side of eastern Japan, compared to 18 two years ago in 2007.
The number of earthquakes is clearly increasing.
Manabu Takahashi, a specially appointed professor of disaster risk management at Ritsumeikan University, explains.
“In the Tokyo metropolitan area, there is the North American Plate, the Philippine Sea Plate, and the Pacific Plate, and there is a possibility of earthquakes occurring near the boundary of each plate. And now, the Pacific Plate is moving more actively. As a result, earthquakes can be triggered at any time on any plate. This is probably the reason why the northwestern part of Chiba Prefecture experienced frequent earthquakes since the beginning of October.
Dr. Toshiyasu Nagao, a visiting professor at Tokai University and director of the university’s Earthquake Prediction and Volcanic Tsunami Research Division, also sounds the alarm about the occurrence of earthquakes in the Tokyo metropolitan area.
“The earthquakes centered in Ibaraki and Chiba were caused by the release of ‘strain’ that had accumulated in the Kanto region. They are still small earthquakes, and not all the strain has been released. The October 7 quake was a magnitude 5.9, but there is still a good chance that a magnitude 6.5 quake will occur in the near future.
Energy is accumulating underground in Kanto, and it is only a matter of time before it erupts.
It’s only a matter of time before it erupts.
“This could lead to a huge earthquake. The epicenter could be in the Tokyo metropolitan area, the Sagami Trough at the entrance to Tokyo Bay, or near the Izu-Ogasawara Trench. If it happens in the Tokyo metropolitan area, the seismic intensity will exceed 7 on the Japanese scale in downtown Tokyo and areas with loose ground. Also, if a huge earthquake occurs near the Izu-Ogasawara Trench, Tokyo will be hit by a tsunami.
As an earthquake-prone country, Japan should be wary not only of earthquakes directly beneath the Tokyo metropolitan area. The risk of a Nankai Trough earthquake is also in the danger zone.
The above mentioned Mr. Nagao pays attention to earthquakes with epicenters in Wakayama Prefecture, which have been observed many times this year, including the magnitude 4 quake on October 15.
He said, “Since the coast of Wakayama Prefecture is a place where earthquakes rarely occur, we can say that this is related to the future Nankai Trough earthquake. The next time a magnitude 5 to 6 earthquake occurs in the Kii Channel or inland in Wakayama Prefecture, we need to keep in mind that there is a risk of a Nankai Trough earthquake.
The government’s Earthquake Research Committee announced in February 2006 that there is a 70-80% probability that a Nankai Trough earthquake will occur within 30 years.
More than three years have passed since then. There is no doubt that the probability is increasing every year.
“The Nankai Trough is already dangerous, but the risk has increased even more due to the increased movement of the Pacific Plate. The area around Lake Hamanako in western Shizuoka Prefecture and Toyohashi in Aichi Prefecture is under particularly strong stress. This is a dangerous area that could be the epicenter of the “Tokai Earthquake” (Suruga Bay to inland areas of Shizuoka Prefecture). It is considered to be at a stage where an earthquake could occur at any time. In addition to this, there is a danger that an earthquake in the Sagami Trough, a Tonankai earthquake off Mie Prefecture, and a Nankai earthquake off Shikoku could occur simultaneously.
The “Nankai Trough Earthquake” may cause further natural threats.
“There is a high probability that the Nankai Trough earthquake will be linked to the eruption of Mt. During the Edo period, the 1707 eruption of Mount Hōei lasted for about two weeks, and volcanic ash poured down on Tokyo. It is certain that the functions of the capital and the economy will be paralyzed.
According to the national government’s estimates, the maximum death toll in the event of an earthquake directly under the Tokyo metropolitan area would be about 23,000. According to the national government’s estimates, the maximum number of deaths in the event of an earthquake directly under the Tokyo metropolitan area would be about 23,000.
We have no choice but to be prepared to survive.
From the November 19, 2021 issue of FRIDAY
Photo： Asahi Shimbun