Why does the Earth have an earthquake?

Earthquakes are the rapid vibrations of the Earth's surface and are also known as geodynamics in ancient times. It is like a wind, rain, lightning, landslides, and volcanic eruptions. It is a natural phenomenon that often occurs on the earth.

There are many causes of the vibration of the earth's surface. According to the cause of the earthquake, earthquakes can be divided into the following categories:

1 . Collapsed earthquakes An earthquake caused by the collapse of an underground cavern or the top of a mine is called a collapsed earthquake. Such earthquakes are small in scale and rare in frequency, and even if they occur, they often occur in limestone cavernous areas or large-scale underground mining areas.

2 . Induced earthquakes Earthquakes triggered by activities such as the impoundment of reservoirs and water injection in oil fields are called induced earthquakes. Such earthquakes occur only in certain specific reservoir areas or oilfields.

3 . Artificial earthquake

4 . Structural earthquakes Earthquakes caused by the dislocation and rupture of deep underground rock formations are called structural earthquakes. This type of earthquake has the largest number of occurrences and its destructive power, accounting for more than 90% of the world's earthquakes.

5. Volcanic Earthquakes Earthquakes triggered by volcanic activity, such as magmatic activities and gas explosions, are called volcanic earthquakes. Volcanic earthquakes can occur only in volcanic activity areas, which account for only about 7% of the world's earthquakes. Ground-induced human-induced ground vibrations such as underground nuclear explosions and explosive blasting are called artificial earthquakes.

In the process of unraveling the mystery of the earthquake, mankind has produced a variety of myths and legends accompanied by abundant imagination. Around the 12th century, the Japanese ancient almanac had a description of the so-called "earthquakes." In 1710, when a Japanese book talked about the relationship between squid and an earthquake, it was thought that the squid was lying low on the ground and backing over the land of Japan. When the squid was angry, it moved its tail and fins and caused an earthquake.

Ancient China also specifically described earthquakes as a special disaster. There is a folk legend that there is a big squid in the ground and it is lying on the ground. It will take a long time to turn over, so the earth will shake and the squid turns to be an earthquake. With the development of science, people have come to understand earthquakes from mythology. In ancient Greece, Epicurus believed that the earthquake was trapped in the earth's crust because of the wind. As a result, the earth's crust broke into small pieces and kept moving, that is, the wind caused the earth to shake and cause an earthquake. As a result, Lukcelushi’s Fengcheng theory said that some kind of tremendous force from the outside world or the earth’s own wind and air suddenly entered the emptiness of the earth. In this huge void, first the turbulent turbulence and the whirlwind started. Then the resulting force is sprayed out of the outside world. At the same time, there are deep cracks in the earth, forming huge cracks. This is an earthquake. Aristotle once again suggested that the earthquake was caused by sudden underground winds and burning flammable objects beneath the ground.

At the beginning of the 20th century, scientists began to study seismic waves in depth, which opened a new page for earthquake science and the entire earth science. There are three hypotheses that have been put forward in greater detail:

First, in 1911, Li De proposed that when the strain energy accumulated within the Earth exceeds the rock strength, a fault will be generated. After the fault is formed, the rock elastically rebounds and restores its original state. Then, the accumulated energy is suddenly released to cause an earthquake. This is called “ Elastic rebound

Second, in 1955, Japan's Matsuzawa Takeo proposed that underground thermal conductivity of rock is uneven, part of the volume of molten expansion, the surrounding rock, resulting in an outburst of surrounding rock, this is the so-called "magmatic impact theory";

Third, the American scholar Bridgeman proposed that “substance change” occurs when the underground material changes from a crystalline state to another crystalline state under a certain critical temperature and pressure and the volume suddenly changes. Although the mystery of the earthquake has not yet been completely solved, the disciplines of physics, chemistry, paleontology, geology, mathematics, and astronomy are called cross-infiltration and deep development. This has made the discipline of seismology make great progress.