Earthquake is the rapid vibration of the earth's surface, also known as earthquake in ancient times. So do you know why earthquakes happen? I hope you can learn from the earthquake and share the reason why it happened.
More earthquake related content recommended ↓↓
What are the safety knowledge of earthquake prevention
Four common sense of earthquake self rescue
Eight instructions for earthquake
Knowledge and principles of earthquake escape
Macroscopic precursory phenomena of earthquakes
The phenomena related to earthquake preparation in nature before an earthquake are called earthquake precursors. Earthquake precursor anomalies include micro anomalies and macro anomalies.
Microscopic anomalies, such as topographic deformation and geomagnetic anomalies, are mainly detected by high-precision scientific instruments.
Macro anomaly refers to the anomaly that people can feel with their senses, mainly including groundwater anomaly, animal and plant anomaly, ground sound, ground light and other anomalies.
1、 Well water change
There is a doorway for abnormal rise and fall due to drought
No rain becomes muddy, discolored and smelly
The air jet sounded again, and the flowers turned and bubbled
This is a macroscopic precursory phenomenon of well water in groundwater.
When the groundwater bubbles, becomes turbid and has peculiar smell, it may be an abnormal reflection before the earthquake. Of course, many reasons can cause groundwater anomalies, and groundwater may also change under the influence of other environments.
2、 Animal abnormality
Before many major earthquakes in history, many animals showed "abnormal behavior" to varying degrees. Therefore, people call animals "living instruments" for observing earthquake precursors.
People make these anomalies into Proverbs:
Mules, horses, cattle and donkeys do not enter the circle, break free from the reins and flee
The pig doesn't eat, the dog barks, and the rabbit jumps up and down
Ducks can't go down, chickens can't go up trees, pigeons can't fly back to their nests
Hibernating hemp snakes come out of their holes early, and rats run all over the street in groups
Loach and leech scurry up and down, and the fish hover on the water
The fine dragonflies move away in groups, and the bees startle the nest and sting people and animals
There are also many factors that cause animal anomalies, so abnormal behavior of animals is not necessarily a precursor of earthquakes.
3、 Ground light and sound
Ground light refers to the phenomenon that people see the sky glow during a major earthquake. The color of ground light has other colors besides blue and white. In general, small earthquakes are not easy to cause earth light phenomenon. The advent of earth light often indicates that large earthquakes will occur soon. Before the Haicheng earthquake in Liaoning Province in 1975 and the Tangshan earthquake in Hebei Province in 1976, the earth light phenomenon was very prominent. If we can quickly and decisively take some shock absorption measures at this time, it is possible to avoid earthquake disasters.
A few minutes or hours before an earthquake, there is often a sound from deep underground, which is called "earth sound". According to the survey, before the Tangshan earthquake, 95% of the residents who did not sleep heard the sound of the earth. These ground noises are relatively low, high and low, which are completely different from the normal urban noise.
Why did an earthquake happen
In fact, until now, science can not explain what the cause of earthquakes is. One explanation that science can give is that earthquakes are a natural phenomenon caused by the movement of surface plates, which is no different from thunder and rain.
Earthquakes are the result of the movement of the earth. During the earth movement, the earth's crust is also moving and changing.
The movement and change of the earth has gradually accumulated huge energy, which has a very strong force on the underground rocks. When the rocks can not bear this force, they will suddenly break and stagger.
Earthquake refers to the surface vibration caused by the release of energy due to the dislocation and fracture of rock mass in the earth's crust. Rock rupture produces seismic waves. When the seismic waves reach the surface, the ground vibrates. This is earthquake.
What are the types of earthquakes
There are three main types of natural earthquakes: volcanic earthquake, subsidence earthquake and tectonic earthquake.
Volcanic earthquake is the ground vibration caused by the impact of magma on the earth's surface due to volcanic eruption. Volcanic earthquake has a relatively small influence range and relatively small damage.
Subsidence earthquake is the ground vibration caused by stratum subsidence. For example, the collapse of underground limestone cave or the collapse of mine goaf will cause small-scale ground vibration. This kind of earthquake generally has little damage.
We usually call earthquakes tectonic earthquakes. Tectonic earthquake is caused by the dislocation and rupture of rock strata deep underground. This kind of earthquake accounts for more than 90% of the number of earthquakes in the world, and its vibration intensity is large and its influence range is wide, so it is the greatest threat to mankind.
Earthquakes are large and small. The magnitude of an earthquake is expressed by magnitude. The stronger the earthquake, the greater the magnitude. According to the magnitude, earthquakes can be divided into the following categories:
The earthquake magnitude is divided into weak earthquake, sensible earthquake, destructive earthquake and serious destructive earthquake.
Weak earthquake: generally refers to an earthquake with magnitude less than 3. This kind of earthquake is usually invisible to people and can only be recorded by instruments.
Sensed earthquake: generally refers to earthquakes above magnitude 3 and below magnitude 5. People can feel such earthquakes, but generally they will not cause damage. There are more than 50000 earthquakes with a magnitude of more than 3 in the world every year.
Destructive earthquake: generally refers to an earthquake of magnitude 5 or above that can cause damage to the surface and its buildings and facilities. On average, there are about 1000 earthquakes with a magnitude of more than 5 in the world every year.
Severe destructive earthquake: refers to an earthquake of magnitude 7 or above. There are 10 to 20 such earthquakes in the world every year, but most of them occur in the sea and deserted places.
For each magnitude difference, their energy difference is more than 30 times, that is, a magnitude 7 earthquake is equivalent to the capacity of nearly 1000 magnitude 5 earthquakes.
When an earthquake occurs, it will produce seismic waves. The vibration people feel is caused by the propagation of seismic waves.
When an earthquake occurs, it is often felt to move up and down first, and then shake left and right. This is caused by the characteristics of seismic waves. Seismic waves are mainly composed of P-waves and S-waves. The propagation speed of P-waves is fast, but relatively weak, making people feel bumpy up and down; S-wave propagation speed is slightly slow, but relatively strong, which can cause huge shaking and serious damage to surface buildings.
In addition to the magnitude of the earthquake and the propagation degree of the epicenter wave, it is also related to the magnitude of the earthquake and the propagation degree of the epicenter wave. We use intensity to measure the damage degree of earthquake. Generally speaking, after an earthquake, the damage in the epicenter area is the most serious and the intensity is the highest. From the epicenter to the surrounding areas, the intensity gradually decreases. An earthquake has only one magnitude, but it can be divided into different intensity areas.
During an earthquake, the place where an earthquake occurs inside the earth is called the source. The point on the ground directly facing the epicenter is called the epicenter. The distance from the source to the epicenter is called the focal depth. The distance from any point on the ground to the epicenter is called epicenter distance.
The earthquake distribution on the earth is not uniform. It can be seen from the world epicenter distribution map that the global earthquake distribution has a certain regularity, mainly distributed in the circum Pacific seismic belt, Eurasia seismic belt and ridge seismic belt.
China is located in the southeast of Eurasia and adjacent to the Pacific Ocean in the East. It is a country with serious earthquake disasters.
From the distribution map of major seismic zones in China, we can know that earthquakes are widely distributed in China, with more than 20 major seismic zones in the country.