Tokyo Metropolitan Earthquake Strain accumulation at this moment

Tokyo Metropolitan Earthquake Strain accumulation at this moment now Prepare for the emergency 8:04 on December 2

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The “Tokyo Metropolitan Earthquake” is said to occur with a probability of 70% within the next 30 years. Experts' analysis shows that the ground in Kanto is pushed north at a pace of up to 2 centimeters a year, and the “strain” that is the energy of the earthquake continues to accumulate at this moment. Experts warn, “The probability of 70% within 30 years means“ it ’s not strange to wake up ”.

The Kanto region is a complex structure in which two plates of the sea, the “Philippine Sea Plate” from the south and the “Pacific Plate” from the east, sink below the plate on the land side, and various types of large earthquakes have repeatedly occurred. It was.

Associate professor Takuya Nishimura of the Disaster Prevention Research Institute at Kyoto University analyzes the movement of the ground using GPS observation data and investigates how much "strain" is accumulated.

According to the analysis, the plate on the land side is pushed northward as the Philippine Sea plate sinks, and the amount of change is larger in the southern Kanto region, and the ground moves about 2 cm per year in the Boso Peninsula and the Miura Peninsula. That is.

Associate professor Nishimura says, “Since the strain builds up in the land, the active faults on the land will move more easily, and so-called“ inland-type earthquakes ”are more likely to occur.

In addition, Associate Professor Nishimura points out that the strains that cause other types of earthquakes deep underground continue to accumulate.

In the area where the Philippine Sea plate is subducted, the Pacific plate subducted from the east is partially blocked, and the plate itself is bent.

This occurs in the Philippine Sea plate, and the earthquake is located in the densely populated areas, with Tokyo, Chiba Prefecture, etc. directly above the epicenter.

Among the earthquakes that the country envisions as earthquakes directly under the Tokyo metropolitan area, 23,000 people will die in the worst case, but the type of earthquake that occurs within the Philippine Sea plate is.

Associate professor Nishimura said, “The probability of an earthquake directly below the capital being 70% within the next 30 years does not mean that it will occur in 30 years, but it will not happen tomorrow. It ’s important to review the preparations and implement the preparations that are possible. ”

What is the Tokyo Metropolitan Earthquake?

The “Tokyo Metropolitan Earthquake”, which can cause enormous damage in the Tokyo metropolitan area, is a magnitude 7 class earthquake predicted by the government's earthquake survey committee with a probability of 70% within the next 30 years.

Regarding this earthquake, a study group of countries made up of experts and others announced the damage estimation and countermeasure direction of the largest class earthquake in 2013 based on the lessons learned from the Great East Japan Earthquake.

There are various types of earthquakes that occur directly under the capital, but damage is expected to occur inside the Philippine Sea Plate, which sinks from the south under the land plate. It is considered to be a large earthquake with a magnitude of 7.3, “directly under the southern part of the city”.

First of all, the magnitude of shaking is assumed to be struck by intense shaking with seismic intensity 7 in Tokyo, Chiba, Saitama and Kanagawa in the Edogawa and Koto wards of Tokyo, and in the four prefectures of Tokyo, Chiba, Saitama and Kanagawa.

It is assumed that the damage will be the greatest when there is an earthquake in the windy “winter” evening of this season, and there are 610,000 buildings that are completely destroyed or burned out. It is said that 2,000 buildings will be destroyed.

The death toll is about 23,000, and about 16,000, or 70% of them, are said to die from fire.

It is estimated that 123,000 people will be injured, 58,000 people will need to be rescued, and the maximum number of evacuees will be 7.2 million.

The impact on lifelines and traffic such as water and sewage and electricity will be prolonged, and there is a risk that railways will not be able to operate for about one week to one month. In addition, heavy traffic jams continue on the general roads in the city for several weeks. It is said that fuels such as water, gasoline, etc. will continue to run short.

The economic damage is estimated to be more than 95 trillion yen, including direct damage to buildings, etc., as well as indirect damage caused by declines in corporate production activities and services.

On the other hand, if thorough precautions are taken, the number of deaths can be reduced to one-tenth, and in order to promote earthquake resistance of buildings and to prevent fires, the power is automatically shut off by detecting shaking. The spread of “seismic breakers” is important.

The basis for the occurrence with a probability of 70% within the next 30 years

The “Tokyo Metropolitan Earthquake” is predicted to occur with a probability of 70% within the next 30 years.

It is derived from the earthquakes that occurred repeatedly in the past.

In the “Sagami Trough” off the coast of southern Kanto, the “Philippine Sea Plate” on the sea side sinks under the land plate, and a “giant earthquake” has occurred in the past at the boundary between the two plates.

The “Genroku Kanto Earthquake” with magnitude of 1703 in 1703 and the “Taisho Kanto Earthquake” with magnitude of 7.9 that caused the “Great Kanto Earthquake” in 1923.

The magnitude 8 class “giant earthquake” that occurs at the plate boundary has a probability of occurring within the next 30 years, ranging from almost 0% to 6%.

On the other hand, during the 220 years between two “giant earthquakes”, many large-scale earthquakes of magnitude 7 class have occurred.

For example, the “Tenmei Odawara Earthquake” of 1782 in the Edo Period, the “Ansei Edo Earthquake” of 1855, the “Meiji Tokyo Earthquake” and “Earthquake Near Tokyo Bay” in 1894 in the Meiji Era, and after entering the Taisho era Eight major earthquakes occurred in 220 years, including the “Earthquake near Uraga Channel” in 1922.

Based on the frequency of these occurrences, the government's earthquake investigation committee announced the probability of the future occurrence of a “directly earthquake in Tokyo” in 2014.

Assuming that one “cycle” is 220 years when two “giant earthquakes” occurred, an average magnitude 7 class earthquake occurred once every 27.5 years.

Based on this, it was derived that “Magnitude 7 class earthquakes directly under the capital will occur with a probability of 70% within the next 30 years”.

The Earthquake Research Committee has pointed out that magnitude 7 class earthquakes appear to have a “quiet period” and an “active period”.

The first half of 220 years was a quiet period, and the last 100 years after the Great Kanto Earthquake was a period of active earthquakes.

It has been 100 years since the Great Kanto Earthquake, but there has been only one magnitude 7 class earthquake in the last 100 years.

The Earthquake Research Committee also shows the idea that there may be more seismic activity in the future.