Japan is one of the most earthquake-prone countries in the world: It is said that about 20% of the world's earthquakes of magnitude 6.0 or greater occur in Japan.
20% of the world's earthquakes of magnitude 6 occur near Japan
10% of all magnitude 5.0 earthquake earthquakes and 20% of all magnitude 6.0 or greater earthquakes occur near Japan.
In Japan, where many earthquakes occur, technology to withstand earthquakes is much more advanced than in other countries. For example, the experience of buildings being destroyed by earthquakes has led to the development of research on building and civil engineering technologies that can withstand large earthquakes. As a result of this research, buildings and bridges are required by law to be designed to withstand large earthquakes.
Japan is famous throughout the world as a country that is particularly prone to natural disasters. For example, although Japan is less than 1% of the world's land area in terms of earthquakes, 20% of the world's earthquakes occur in Japan. Japan also accounts for more than 20% of the total amount of damage caused by natural disasters worldwide.
Japan is located in a seismically active area of the earth.
The Earth is mainly composed of rocks, but the deeper underground you go, the higher the temperature becomes, which causes a convective flow of material called "mantle" inside the Earth. Near the Earth's surface, the mantle is formed into plates, which are several 10 to 100 km thick and move at a rate of several centimeters per year. There are 14 to 15 such plates on the Earth's surface, and they move in different directions as the mantle convects in the Earth's interior.
At the boundaries where the plates collide, one plate is subducted under the other plate. As a result, the ground rises to form high mountains, and if the subduction zone is an ocean, it becomes a deep "trench opening.
Earthquakes are caused by frictional friction between the plates. The locations in the world where earthquakes occur are around the points where the plates collide.
Japan is located at the convergence of four plates, which is rare in the world.
The Pacific Plate moves westward and collides with the North American Hokubei Plate, which then burrows underground at the Japan Trench Trench Opening and other points. The Philippine Sea Plate moves northward and collides with the North American Northwest Pacific Plate, which then encounters the Nankai Trough and encroaches underground. Friction and friction between these plates causes earthquakes.
The Japanese Islands are also moving on top of the plates
The Pacific Plate and the Philippine Sea Plate push the Pacific side of the Japanese Islands to the west and northwest, while the Eurasian Plate pushes the Sea of Japan side of the Japanese Islands to the east and southeast.
In the southern part of the Kanto region, centering on Tokyo, a large earthquake of magnitude 8 on the Richter scale, similar to the Great Kanto Earthquake, occurs once every 200 to 300 years. In the past, two major earthquakes of magnitude 8 on the Richter scale occurred in 1703 and 1923. Therefore, it is expected that a magnitude 8 earthquake will not occur for another 100 years or so.
However, there have been several magnitude 7 earthquakes in the area directly under the Kanto region during the time of the magnitude 8 earthquake. Since the earthquake is expected to occur directly under the Kanto region, there is concern that a magnitude 7 earthquake earthquake will occur directly under Tokyo.
It is estimated that there are about 2,000 active faults in Japan
One of the causes of seismic tremors is "active faults. Active faults and ruptures have repeatedly caused seismic tremors in the past and are expected to continue to do so in the future.
Japan has been severely damaged by tsunamis
After an earthquake with its epicenter at the bottom of the ocean, we must be careful of tsunami waves.
When an earthquake occurs, the ground near the epicenter rises and falls violently. This causes a sudden surge of seawater, which becomes a large wave that spreads out in all directions.
The deeper the ocean, the faster the tsunami waves travel, and the shallower the ocean, the slower they travel. At a depth of 5,000 meters, a tsunami wave travels as fast as a jet airplane, and at a depth of 100 meters, it travels as fast as a car on the highway.
Magnitude is the unit of energy of an earthquake
When the magnitude increases by 0.2, the energy is about twice as great; when the magnitude increases by 1, the energy is about 32 times greater; and when the magnitude increases by 2, the energy is about 1000 times greater. The energy of an earthquake of magnitude 2.0 is not twice as great as that of an earthquake of magnitude 4.0, but 1,000 times greater.
An earthquake of large magnitude will be felt far away from the epicenter. The closer to the epicenter, the stronger the tremor. Small magnitude earthquake shocks are not transmitted far. They do not shake strongly even if they are close to the epicenter. However, if the earthquake occurred shallow underground, the seismic intensity will be stronger the closer the distance to the ground is.
How much does the intensity of an earthquake earthquake differ depending on the seismic intensity scale?
The seismic intensity is measured by a machine called a seismic intensity meter. The seismic intensity scale detects the shaking of an earthquake and uses a calculation formula to determine the seismic intensity scale.
There are 10 levels of seismic intensity: "seismic intensity 0," "seismic intensity 1," "seismic intensity 2," "seismic intensity 3," "seismic intensity 4," "seismic intensity 5 weak," "seismic intensity 5 strong," "seismic intensity 6 weak," "seismic intensity 6 strong" and "seismic intensity 7".
