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What is the earthquake?
[ Author: Release time: 2016-02-10 16:12. Source: Kunming earthquake prevention and disaster reduction Bureau ]

1, what is the earthquake?

Earthquakes are commonly referred to as earthquakes. It is a natural phenomenon like wind, rain, thunder, solar eclipse, lunar eclipse, volcanic eruption, mud rock flow and landslides. Generally speaking, earthquakes mainly refer to tectonic earthquakes. Tectonic earthquakes are caused by the continuous movement and interaction of the earth's crust, causing the deformation of the underground rock layers and gradually accumulating great energy. When the deformation exceeds the bearing capacity of the weak parts, it suddenly breaks and moves, and at the same time, it carries out the propagation of energetic elastic waves around them. When these waves reach the earth's surface, the ground vibrates, and people feel the earthquake. If the ground vibration caused by the earthquake is very strong, it will cause housing collapse, collapse and collapse, and bring great harm to human life and property.

2, what are the aspects of earthquake damage?

The destruction of earthquakes includes two aspects: first, the destruction of the natural environment; and the two is the destruction of artificial facilities.

The destruction of the natural environment by earthquakes is the collapse or landslides of the mountains, surface cracks, collapse, uplift or sandblasting. The great earthquakes that occur on the seabed sometimes cause great destructive tsunamis.

The destruction of artificial facilities by earthquake mainly lies in the destruction of building structures, such as the destruction of housing facilities, and so on. The destruction of lifeline projects mainly refers to the damage of water, electricity, transportation and communication facilities, and so on.

3, what are the characteristics of earthquake disasters?

Compared with other disasters such as floods, droughts, typhoons and plagues, earthquake disasters have the following characteristics:

(1) sudden and strong. The earthquake occurred very suddenly, lasted for only a few seconds or dozens of seconds, but in such a short period of time, it will cause buildings collapse, bridge breakage, casualties and other disasters. People are not prepared for time from ideology to material. If there is no time to take any measures, disasters will come, so the prevention is difficult and the consequences are serious.

(2) destructive. Large earthquakes in densely populated and economically developed areas often result in heavy casualties and huge economic losses. For example, in 1976, the magnitude 7.8 earthquake in Tangshan killed more than 24 people and left the whole city in ruins.

(3) the influence is extensive. After the strong earthquake, not only heavy casualties, huge economic losses, serious impact on people's normal life and economic activities, but also great trauma to people's hearts, such wounds can not heal in a short time.

(4) strong linkage. In addition to disasters caused by building damage, a series of secondary disasters, such as fires, floods, tsunamis, landslides, debris flows, gas leakage, disease epidemics, and radioactive pollution, will also occur after the earthquake. Especially in modern urban areas, once the earthquake occurs, the power supply system will be disrupted, the traffic will be interrupted, the communication system and network system will be paralyzed, and the water supply, gas and oil pipelines will burst, causing more serious disasters and losses, which will directly affect social stability and people's normal life.

4, what are the common terms of earthquakes?

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(1) earthquake source: the initial origin of earthquake motion, which refers to the fracture, dislocation and excitation of seismic waves in the deep crust.

(2) epicenter: the vertical projection point of the source on the ground, which is directly opposite the focal point on the ground. Strictly speaking, the epicenter is not a point, but a region. The epicenter measured by seismographs is called the microseismic epicenter. The area with the most serious damage is called the epicentre. The geometric center of the epicentre is called the epicenter. Because the distribution of crustal faults is different, the macroscopic epicenter is not necessarily consistent with the microseismic epicenter. The epicentral area is called the epicentral area.

(3) focal depth: the vertical distance from the epicenter to the focal point.

(4) epicentral distance: the distance between the ground surface and the epicenter.

5. What are the classifications of earthquakes?

According to different angles and needs, there are many different classification methods.

(1) according to the origin of earthquakes, there are:

Tectonic earthquakes: earthquakes caused by the dislocation of underground strata, and 90% of the natural earthquakes in the world are tectonic earthquakes.

Volcanic earthquakes: earthquakes caused by volcanic eruptions or underground magmatic activities account for about 7% of the total number of earthquakes worldwide.

Collapse earthquake: earthquake caused by ground subsidence, such as mine collapse.

Induced earthquake refers to earthquakes caused by human engineering activities such as reservoir storage, mining water injection or pumping.

Artificial earthquake: an earthquake triggered by underground nuclear explosions and industrial blasting.

(2) according to focal depth, there are:

Shallow earthquakes: earthquakes with a focal depth of less than 70 km are also known as normal deep earthquakes. Most destructive earthquakes are shallow earthquakes.

Intermediate source earthquake: an earthquake with a focal depth of 70 km to 300 km.

Deep source earthquake: an earthquake with a focal depth of over 300 km, so far, the deepest earthquake recorded in the world has a focal depth of 786 km.

(3) according to epicenter distance,

Local earthquake: an earthquake with an epicentre less than 100 km away.  

Near earthquake: an earthquake with an epicentral distance between 100 and 1000 km.

Teleseismic: an earthquake with an epicentral distance greater than 1000 km.

(4) according to magnitude scale, there are:

Microfracture: generally refers to a subsurface medium or fault micro rupture caused by a weak earthquake with magnitude less than zero. Only seismometers with high magnification can be observed.

Micro earthquake: the magnitude is between 0 and 1.9, which is generally not felt, and can be observed by seismograph.

Small earthquakes: the magnitudes are between 2 and 3.9, and are felt in small areas near the epicenter and nearby, but without damage.

Light earthquake: the magnitude is between 4 and 4.9. Most people in the epicenter area strongly feel that if the source is shallow, it may cause slight damage to some buildings in the epicenter, but the damage is generally limited.

Moderate strong earthquakes: the magnitudes are between 5 and 5.9, which are destructive earthquakes. Generally, the intensity of the epicentral area can reach VI to VII degrees, and there are casualties.

Strong earthquakes: the magnitudes are between 6 and 6.9, and larger destructive earthquakes generally cause damage of VII to VIII degrees, which can be as high as IX degrees.

Large earthquakes: the magnitude is between 7 and 7.9, and strong destructive earthquakes can cause serious damage to IX or above, which will cause huge losses to the social economy and people's lives and property, and some earthquakes can cause tsunamis.

Giant earthquake: the earthquake with a magnitude greater than 8 is extremely devastating. The intensity of the epicenter can reach X to XII degrees, and some earthquakes can cause huge tsunamis.