Earthquake precursors, how to divide the magnitude, what is an earthquake, and how the earthquake is formed.

Earthquake is a phenomenon in which the local medium in the earth ruptures rapidly, producing seismic waves, thus causing ground vibration in a certain range. Earthquake is the rapid vibration of the earth's surface, which was also called earthquake in ancient times. Like wind, rain and lightning, it is a natural phenomenon that often happens on the earth. Ground vibration is the most intuitive and common manifestation of earthquakes. Strong earthquakes at the bottom of the sea or in coastal areas will cause huge waves, which is called tsunami. Earthquakes are extremely frequent, and there are about 5 million earthquakes every year in the world.

The place where seismic waves are emitted is called the source. The vertical projection of the source on the ground, and the point closest to the source on the ground is called the epicenter. It was the first place to receive vibration. The depth from the epicenter to the source is called the focal depth. Generally, the focal depth less than 70km is called shallow earthquakes, the depth of 70-300km is called Zhongyuan earthquake, and the depth greater than 300km is called deep earthquake. Earthquakes of the same size have different damage degrees to the ground due to different focal depths. The shallower the source, the greater the damage, but the smaller the spread, and vice versa.

Destructive earthquakes usually occur in shallow earthquakes. For example, the focal depth of the Tangshan earthquake in 1976 was 12km.

The strongest ground motion of a destructive earthquake is called the extreme earthquake zone, which is often the area where the epicenter is located.

The distance from a place to the epicenter is called epicentral distance. Earthquakes with epicentral distance less than 1000 km are called near earthquakes, earthquakes with epicentral distance between 100- 1000 km are called near earthquakes, and earthquakes with epicentral distance greater than1000 km are called teleseisms. Among them, the farther the epicentral distance, the smaller the impact and damage.

The ground vibration caused by earthquake is a complex movement, which is the result of the joint action of longitudinal wave and shear wave. In the epicenter, longitudinal waves made the ground jump up and down. Shear waves make the ground shake horizontally. Because longitudinal waves travel faster and decay faster, while shear waves travel slower and decay slower, they are far from the epicenter, so you often can't feel jumping up and down, but you can feel horizontal shaking.

When a large earthquake occurs in a certain place, a series of earthquakes often occur within a period of time, the largest of which is called the main earthquake, the earthquake before the main earthquake is called the foreshock, and the earthquake after the main earthquake is called the aftershock.

Magnitude refers to the magnitude of an earthquake and is an index to measure the intensity of an earthquake. It is determined by the energy released by each seismic activity measured by seismograph. The magnitude is usually represented by the letter M. At present, the standard of magnitude used in China is the international Richter scale, which is divided into 9 levels. Earthquakes with a magnitude less than 2.5 are usually called small earthquakes, earthquakes with a magnitude of 2.5-4.7 are called inductive earthquakes, and earthquakes with a magnitude greater than 4.7 are called destructive earthquakes. The magnitude difference per 1.0 and the energy difference are about 30 times; For every difference of 2.0, the energy difference is about 900 times. For example, an earthquake of magnitude 6 released energy equivalent to the atomic bomb dropped by the United States in Hiroshima, Japan. An earthquake of magnitude 7 is equivalent to 32 earthquakes of magnitude 6, or 1000 earthquakes of magnitude 5.

According to the magnitude, earthquakes can be divided into the following categories:

The magnitude of a weak earthquake is less than 3. The magnitude of the felt earthquake is equal to or greater than 3 and less than or equal to 4.5.

The magnitude of moderate-strong earthquakes is greater than 4.5 and less than 6. The magnitude of a strong earthquake is equal to or greater than 6. Among them, the magnitude greater than or equal to 8 is also called a giant earthquake.

One:

Cattle, horses, donkeys and mules don't enter the stables, pigs don't eat, and the archway is noisy.

The goat's uneasy and painful voice made the rabbit prick up its ears and jump.

The dog barked at the house and the domestic cat ran away in horror.

Chickens don't enter the nest, and pigeons in the tree fly away and don't return to the nest.

Rats are busy moving in groups, and weasels are running in groups.

Ice and snow, snakes out of holes, hibernating animals.

Listen to a group of directional flying bees. The bees have left.

Frogs and toads were silent, and fish jumped on the water with their white bellies turned over.

Pheasants croak, cicadas don't croak under trees.

Tigers and leopards in the garden don't eat pandas and elk.

When the oars went ashore, the goldfish came out of the tank and the birds were noisy.

Two:

1. As soon as the noise came out, the earthquake came.

2. The sound of a big earthquake is heavy, and the sound of a small earthquake is sharp.

3. Loud, far away; Short ring, not far.

Listen to the sound first, then move, and act quickly when you hear the noise.

5. Jump up and down and sway back and forth for half a day.

6. Follow closely and jump up and down; Far away, swinging from side to side.

7. Up and down, in front of you; Wandering in the sky.

8. The house is in the east, and the earthquake is coming; If it swings north and south, it will come north and south.

9. Sand and water blow along the road, and the old river is underground.

10. What is the most water and sand sprayed? Needless to say, it's wet and alkaline.

1 1. When tofu is extruded, water comes out and slag comes out; When the earthquake broke out, water and sand were ejected.

12. The depression is heavy and the flat land is light; The sand is heavy and the land is light.

13. Brick-wrapped adobe walls have the worst seismic capacity.

14. Brittle in bumps, but in swings.

15. parapets, eaves and earthquakes are the most unlucky.

16. The foundation is relatively solid and far from the river; The wall is better and the connection is closer; The house is shorter and the roof is lighter; Reasonable layout and simple appearance. If you want to be better, learn more from each other.

17. Earthquakes often bring rainfall, either suddenly or violently.

18. Pay more attention to your work at home on the fifteenth day of the lunar calendar.

19. Well water is a treasure, and the precursor comes early.

20. Groundwater has a precursor: it is either rising or falling; Sweet becomes bitter, bitter becomes sweet; Muddy, muddy Yes, I want to report it. Why? Make a prediction

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