Earthquake knowledge

Earthquake is what people usually call ground motion, which is ground vibration detected by feeling or instrument. Like wind, rain and electricity, it is a very common natural phenomenon and a manifestation of crustal movement. It is due to the change of the rotation speed of celestial bodies in the process of crustal movement, inside and outside the earth and the earth, which leads to the stress imbalance in different parts of the earth's crust, and is subjected to extrusion, tension, torsion and other forces respectively. In those areas where the ground stress is concentrated and fragile, it is easy to rupture, causing fracture changes and earthquakes.

2. What is the source, epicenter and focal depth?

Earthquakes occur in the crust and upper mantle, and we call the place where earthquakes occur on the earth the source. In theory, the source is often regarded as a point, but in fact it is a region with a certain scale. The epicenter is the projection of the source on the ground. In fact, the epicenter is not a point, but an area, which is the epicenter. The focal depth is the vertical distance from the focal point to the ground. According to the focal depth, earthquakes can be divided into shallow earthquakes, moderate earthquakes and deep earthquakes.

3. Where do earthquakes often occur?

The occurrence of earthquakes is controlled by geological structures. Therefore, the distribution of earthquakes mostly occurs in the active tectonic belt within the active tectonic system, and mainly in the places where active faults exist. In other words, the occurrence of earthquakes is mainly related to active faults.

4. Which countries have more earthquakes in the world?

Earthquakes in the world are mainly distributed in the following two zones: (1) Pacific Rim seismic zone: including the Pacific coast of North and South America and from Aleutian Islands, kamchatka peninsula, Thousand Islands and Japanese Islands, south to Taiwan Province Province of China, southeast through Philippine Islands, and finally to New Zealand.

(2) Himalayan-Mediterranean seismic belt: from India and Nepal through Myanmar to Hengduan Mountains and Himalayas in China, across Pamirs, and through Central Asia to the Mediterranean and its vicinity.

The energy released by the above two seismic zones accounts for about 98% of the total energy released by global earthquakes. China is just between two earthquake zones, and it is a country with many earthquakes.

5. Is there a precursor to the earthquake?

Various abnormal phenomena closely related to the occurrence of earthquakes before earthquakes are called earthquake precursors. Therefore, the earthquake is a precursor. Earthquake precursors are divided into macro precursors and micro precursors. Macroscopic precursors refer to those that people can directly feel or see with their eyes, including abnormal reactions of animals and things, groundwater changes, meteorological changes, small earthquake activities and so on. Microscopic precursors refer to those that people can't directly see or feel, but can only be measured by instruments, such as crustal deformation, ground tilt and sea level fluctuation, changes in chemical composition of groundwater, changes in propagation speed of seismic waves, weak changes in geoelectricity, geomagnetism, ground temperature and geostress, and small earthquake activities that people can't feel.

6. What is the earth sound?

An earthquake is the sound made underground during an earthquake. Most of these sounds are accompanied by earthquakes, which are mainly manifested as: the roar of strong winds or mountain torrents, the roar of soldiers, the sound of motors, thunder or muffled thunder, the "click" sound of broken trees or the roar of crawler tractors and tanks when they are started, the sound of tearing cloth, and so on. Earthquake, landslide, liquid or gas gushing or explosion from the earth's crust, migration within the earth, etc. Can cause sound. Due to the differences in sound source medium, energy, propagation medium, distance, human experience and mental state, and the reflection and refraction of different landforms, people naturally describe the earth's sound in various ways, each with its own characteristics.

Geosound is the result of the structure and structure of underground rocks and the movement of liquid and gas contained in them, and a considerable part of it is a sign of impending earthquake. Mastering the knowledge of geosound has many benefits for emergency avoidance and disaster prevention.

7. What is terrestrial light?

Luminous phenomena on the ground or in the sky before or at the same time of the earthquake have different shapes and colors, which are called terrestrial light. Like the sound of the earth, it is also a warning of an impending earthquake. Similarly, taking decisive measures immediately after seeing the ground light can reduce the harm. 1February 4, 975, before the Haicheng earthquake, when the train from Dalian to Beijing was about to arrive at Tangwangshan Station, it suddenly saw bright purple light in front of it. The driver thought it was a ground lamp and the train stopped suddenly. Before the train stopped, there was an earth-shattering noise and a strong crack. The train shook violently, but there was no danger because it stopped.

There are different forms of ground light, which can be divided into low-altitude atmospheric light, corona discharge light and underground material streamer.

There are lightning, fireball, flake, strip, column or searchlight, scattering and so on. Some light on the earth does not move, others move and walk in space, or change with time.

8. What was the reason for groundwater fluctuation before the earthquake?

Before the earthquake, sometimes the weather was dry, but well water (groundwater) soared and even overflowed the surface. Well water should have gradually increased in rainy season, but it dropped sharply or even dried up. In some places, there is no water source, but a lot of water gushes out of the ground and so on. The reason is that in the process of earthquake preparation, due to the role of geostress, the geostress is constantly increasing, especially near the epicenter; Crustal activity has intensified. The water level in the extrusion zone will gradually rise; Under the action of tensile stress, the water level in the tensile area will gradually decrease. In particular, the local area of the earth's crust is damaged, deformed or accelerated under the action of geostress, and the water between the upper and lower layers caused by the destruction of rock strata will make the water level rise and fall sharply, which is the basis for using groundwater to predict earthquakes.

9. Before the earthquake, what meteorological anomalies often appeared?

Before an earthquake, especially before a strong earthquake, there will always be some climate and weather anomalies. Such as thermal anomalies, are very obvious before some earthquakes. 17.3 days before the Xingtai earthquake on March 8, 1966, the average temperature rose from-0/3 degrees to 1 1 degrees above zero. Ten days before Haicheng1February 4, 975 earthquake with magnitude 7.3, it was 3.7 degrees higher than the same period of last year. The explosive temperature rise from 8: 00 to 9: 30 12 degrees on the day of the impending earthquake made the cold winter sultry.

This abnormal phenomenon is due to the fact that the earthquake-prone area is on the eve of the violent change of the crust, and before the rupture, the underground heat energy has been violently diffused and transported to the atmosphere by some means. This thermal anomaly has a small range and a short duration.

Some experts have come to the conclusion that in a certain period of time one year or several years before the earthquake, drought first followed by waterlogging, or flood followed by drought; Or drought and flood alternate, followed by a big earthquake. Such earthquakes occur both at home and abroad, such as the Nantong earthquake of 1970. In the first two or three years, a once-in-a-century flood occurred, which triggered a major flood, and then a rare drought occurred. 1989 alternating drought and flood occurred before Daming earthquake in Hebei province. Other phenomena include strange wind, lewd rain, yellow dust and atmospheric turbidity before the earthquake.

10. How to identify macroscopic anomalies of earthquakes?

There will be a variety of macro anomalies before earthquakes, which has been confirmed by a large number of seismic activities. How to identify is a complex problem. Generally speaking, there are weather factors (such as fish floating and frog migration), physiological factors (such as animal illness and estrus), environmental factors (such as water pollution), enemy invasion and so on. Non-seismic groundwater anomalies are caused by natural factors, including meteorological, hydrological, geological and biological interference factors. Human factors include irrigation, water injection and drainage. Non-earthquake plant abnormal factors include plant diseases and insect pests and meteorological anomalies. The characteristics of macroscopic anomalies before earthquakes are as follows: firstly, they are not caused by the above non-seismic factors; Secondly, macro anomalies are regular, spatially controlled by geological structures, synchronized in time, and have a wide range of types and a large number. Of course, if the earthquake is abnormal, it must be determined by combining the change of seismic activity and other microscopic precursor monitoring means.

1 1. What are the causes of sand blasting and water gushing during the earthquake?

During the earthquake, due to the cutting of the underground aquifer by the ground fissure, the groundwater is squeezed, and the mud and sand are carried out of the surface along the fissure, that is, sand blasting and water inrush are formed. Black water and red water appear in some places because the underground soil is black silt or red yellow mud layer, which is brought out of the surface during the earthquake.

12. Why did the ground bump first and then shake during the earthquake?

When an earthquake occurs, it bumps first and then vibrates, which is caused by the different propagation speeds and modes of seismic waves. The propagation of seismic waves is usually divided into two types, one is called body wave in the earth, and the other is called surface wave along the surface and rock surface. Body waves are divided into longitudinal waves and shear waves. The longitudinal wave propagates to the surface first, with a speed of 7-8km/s between1-20km, the slowest propagation speed of shear wave is only 4-5km/s, and the slowest propagation speed of surface wave is only 3km/s.. Due to the physical characteristics of the waveform when the longitudinal wave propagates, the ground objects bump up and down, which makes people feel that they are moving up and down first. The shear wave is slow and comes late. Its waveform is characterized by shaking objects from one side to the other. So people think that after moving up and down, moving left and right, and connecting together, the earthquake comes, first bumping, then shaking.

13. What is an earthquake disaster?

A strong earthquake will cause strong ground vibration, which will directly and indirectly cause damage. Direct damage caused by strong ground vibration, such as ground fracture, deformation, water inrush, sand blasting, building damage and collapse, human and animal casualties and property losses. This kind of damage caused by earthquake is collectively called earthquake disaster.

14. What is an earthquake secondary disaster?

Earthquake secondary disasters refer to: landslides and mudslides caused by strong earthquakes; The dam burst, causing floods; Plague prevailed after the earthquake; Flammable and explosive substances are ignited to cause fire and explosion, or toxic gas leaks due to pipeline damage, and the spread of bacteria and radioactive substances threatens human and animal lives. , collectively referred to as secondary disasters.

Cities are highly concentrated areas of various lifeline projects, and there are various pipe networks on the ground and underground, especially earthquake secondary disasters. All major earthquakes at home and abroad have different degrees of performance. For example,1February 4, 1975 Haicheng earthquake of magnitude 7.3, Angang stopped production of blast furnace due to power failure and water freezing; Yingkou hydropower facilities were destroyed, the city was cut off from water and electricity, and the beaches in the city were paralyzed. 1On July 28th, 976, Tangshan earthquake of magnitude 7.8 interrupted the power supply of Kailuan Mine, and the water inflow soared, and the mine was flooded. A century-old landslide in Tianjin soda plant killed more than 30 people; The valve in the chemical plant was damaged, chlorine gas overflowed and five people were poisoned. On June 1964 and 19, an earthquake of magnitude 7.5 occurred in Niigata, Japan, and the oil depot caught fire. The fire burned for 360 hours until the crude oil ran out, leaving more than 300 houses and factories in no one lives. 1April, 906 18, San Francisco, USA, M = 8.3 earthquake, the stove overturned and caused a fire, and the water supply system was destroyed. The fire lasted for three days and nights, and the urban area of 10 square kilometers was reduced to ashes.

15. What caused the fire during the earthquake?

After a strong earthquake, with the collapse of houses, the power grid was pulled off, and the destruction of gas, oil depots, oil and gas pipelines or inflammable and explosive dangerous goods encountered open flames; It caused a fire again. According to historical records, fire is the most common secondary disaster during earthquakes.

For example, during the September 1 0923 Kanto earthquake of magnitude 8.3 in Japan, a fire broke out in Yokohama 208, which is more than 90 kilometers away from the epicenter. After burning for three days and nights, Yokohama was basically burned out. In Tokyo, which is more than 0/00 kilometers away from the epicenter, a fire broke out on 139 half an hour later, and flammable and explosive chemicals and oils became more and more popular. Coupled with the narrow streets, fire engines can't get in, water sources are cut off, and fires spread. Of the 500,000 houses destroyed, 400,000 were destroyed by fire. Of the100000 people who died, more than 90000 were killed by fire.

16. Why should we pay attention to floods during earthquakes?

If there is an earthquake along the coast, it will stir up huge waves and trigger a tsunami. When it happens near the reservoir, it is easy to cause the dam to crack and appear unexpected danger. Especially the reservoir, if broken, will cause considerable losses. For example, in June 1786 and 1, an earthquake of magnitude 7.5 occurred in Kangding South, Sichuan Province, China. Landslides along the Dadu River caused the river to freeze, and the river burst ten days later. Dozens of feet high floods surged down, flooding1000000 people. Therefore, we should do a good job in preventive work such as seismic reinforcement and be prepared.

17. How did the earthquake damage the house?

The destruction of houses during the earthquake is the result of the strong impact of seismic waves in a short time. The impact of seismic waves causes complex vibration of buildings. When the seismic capacity of the building is exceeded, the building will be destroyed. The impact of seismic waves has two aspects: vertical impact is up-and-down vibration, which causes transverse cracks between roof and wall, foundation and wall root; The horizontal impact is shaking from side to side, causing the wall to crack and collapse vertically, while the roof moves horizontally. Cracks, dislocations and subsidence will also occur on some ground in the epicenter area. If the foundation of the house is in these parts, the damage to the house will be even greater.

18. Can earthquakes be predicted?

In the period before the earthquake, there will always be some abnormal changes near the earthquake zone. Such as the change, sudden rise, sudden drop or bad taste, turbidity, ringing and bubbling of groundwater. Meteorological changes, such as sudden cold weather, sudden heat, drought and flood, electromagnetic field changes, abnormal reactions of animals and plants before earthquakes, etc. Through the comprehensive study of these reactions, coupled with the processing and analysis of observation data by professional departments from the aspects of earthquake mechanism, seismogeology, geophysics, geochemistry, biological changes, celestial influence and meteorological anomalies, the time, place and magnitude of earthquakes can be predicted. For example, 1975' s successful prediction of Haicheng M = 7.3 earthquake is an example. However, due to the complexity of the causes of earthquakes and the suddenness of earthquakes, as well as the limited scientific level of people at present, earthquake prediction is still a worldwide problem, and there are no reliable methods and means to accurately predict all destructive earthquakes in the world. Therefore, seismologists and experts all over the world are trying to explore.

19, what is the significance of group monitoring and prevention in earthquake prediction?

China earthquake work implements the system and policy of combining central earthquake work with local earthquake work, and combining professional teams with group investigation teams. The earthquake work in China, especially the earthquake prediction work, not only has strong task, exploration and sociality, but also has strong locality and mass. Group monitoring and prevention in earthquake work in China has accumulated rich experience for successful earthquake prediction, which constitutes a major feature of earthquake work in China and is of great significance in earthquake prediction.

First, China has a vast territory, but the density of professional precursor network is insufficient. Local stations, enterprise stations and a large number of mass observation points make up for the shortage of professional networks and means, and improve the ability of earthquake monitoring and prediction in China.

Second, due to the wide distribution and control of the mass observation team and the masses who have mastered earthquake knowledge, they are familiar with the local situation, have close ties with local governments, and are close to the earthquake zone. Group monitoring and prevention teams play an irreplaceable role in short-term and imminent earthquake prediction.

Third, the group prevention and treatment team can play a key role in information release and information reporting. Especially in the sudden stage of earthquake precursors, because the impending earthquake anomalies are very short, only a day or two or even a few hours, especially the collection of a large number of macro anomalies, how to find, verify and report in a very short time is very important. Therefore, before and after the earthquake, the group monitoring and prevention team played an important role in being a good staff officer and organizing the masses to prevent earthquakes.