Weather forecast of Changshu broadcasting network
As the saying goes, an earthquake is an earthquake. What caused the earthquake? In ancient times, people lacked understanding of the earth, thinking that the earth under people's feet was carried on their backs by big whales. When whales were tired, they wanted to turn over, causing the earth to shake. Others say that "the earth is angry" means "hugging people" and so on. Scientists tell us that earthquakes are just natural phenomena of sudden tremor of the earth's crust. Because of the different causes of crustal vibration, earthquakes can be divided into tectonic earthquakes, volcanic earthquakes and subsidence earthquakes.
Tectonic earthquake is an earthquake caused by rock fracture, dislocation movement and great changes in geological structure, so it is called tectonic earthquake, also known as fracture earthquake. Most earthquakes in China and the world belong to this kind of earthquake. The focal depth of a tectonic earthquake is usually within 60 kilometers. An earthquake with a depth of about 70-300 kilometers is called a moderate-deep earthquake. Earthquakes with a depth of more than 300 kilometers until about 700 kilometers are called deep earthquakes. All deep-seated seismic areas usually coincide with the strike of the Pacific deep-sea trough far from the coastlines of South America and Asia. Scientists now believe that the trough is a sign of the position where several huge moving parts of the earth's crust collide and pile up with each other. After a period of stalemate, the rocks began to deform. When the deformation of rock strata exceeds its maximum limit, it will suddenly break and move, thus producing an earthquake. This view is more convincing.
Not long ago, a scientist at the California Institute of Stratigraphy suggested that the frequent strong wind force on the earth's surface may be one of the important driving forces for inducing earthquakes. 1September 1986 and1June 1987+00, several moderate earthquakes of magnitude 4.5 occurred in southern California. Before these earthquakes, the scientist monitored and recorded the wind changes in this area in detail. He found that 4-6 weeks before each earthquake, a series of unusually strong high pressure appeared in the earthquake area, which led to strong winds in the Pacific Ocean hundreds of miles near the California coast. He believes that these high pressures and strong winds caused the earthquake. However, this is just a family statement.
Earthquakes caused by volcanic eruptions are called volcanic earthquakes. This kind of earthquake coincides with volcanic eruption. It is the crustal vibration caused by the energy impact caused by volcanic eruption. Volcanic earthquakes are sometimes quite strong, such as those caused by volcanic eruption in caracalla, which stirred up waves as high as 30 meters and shattered the walls and windows of Jakarta 150 kilometers away. However, the area affected by this kind of earthquake is usually limited to tens of kilometers near the volcano, and the frequency of occurrence is less, accounting for only about 7% of the number of earthquakes, causing less harm.
Collapse earthquakes are usually caused by cave collapse. For example, in karst areas where limestone is developed, occasional cave collapses or large rocks fall, which may cause small earthquakes. Cave collapse will also occur after salt mounds and soft strata are eroded by groundwater. The number of such earthquakes is even smaller, accounting for only about 3% of the total number of earthquakes, with small magnitude, limited impact and small losses.
Sometimes, under man-made conditions, it may also cause a collapse earthquake. For example, after the underground ore body is mined, the surrounding rock loses its support, which often leads to collapse and earthquake. This kind of earthquake sometimes causes disastrous losses. This phenomenon often occurs in Canada, South Africa and other countries, especially in coal mines.
Earthquake is a terrible "natural disaster" in people's minds, and many people turn pale when they mention it. In fact, most earthquakes are so small that only sensitive instruments can detect them. Most earthquakes that people can feel occur in sparsely populated mountainous areas. China is a country with frequent earthquakes, and hundreds or even thousands of earthquakes occur every year. However, it takes decades or hundreds of years to encounter an earthquake as destructive as the Tangshan earthquake.
Earthquake is a natural phenomenon. It can be divided into several types according to the different causes.
Tectonic earthquake. It is caused by the in-situ stress produced in the hard strata of the crust and upper mantle in the year of crustal movement, which breaks or revives the original fault. The occurrence of tectonic earthquakes is often sudden, but its gestation process is very long. In the initial stage of in-situ stress, the rock stratum has a certain strength and will not break immediately. When the local stress increases and reaches a certain limit, the rock stratum breaks and an earthquake occurs. Tectonic earthquakes caused by faults or fault activities account for 90% of the total number of earthquakes in the world. Almost all of these strong earthquakes belong to this type, such as 1960 southern Chile earthquake with magnitude 8, 1966 Xingtai earthquake with magnitude 7.2, and 1976 Tangshan earthquake in China with magnitude 7.8. This kind of earthquake is very harmful to human beings.
Volcanic earthquake. Earthquakes caused by volcanic activity are called volcanic earthquakes. When hot magma gathers, expands and erupts in the crust before eruption, the huge impact force can cause rock fracture or fault dislocation, which will lead to earthquakes. Volcanic earthquakes have their own characteristics: the influence range is small, and they appear in the form of small earthquakes. 1000 small earthquakes occurred in succession within a few days after the eruption of Montsoufriere volcano in the Caribbean islands in August 1976. According to statistics, about 7% of earthquakes in the world belong to volcanic earthquakes.
Collapse earthquake. Collapse earthquakes often occur in areas where limestone and other soluble rocks are distributed. This is because karst rocks have been eroded by groundwater for a long time and formed many caves, the top of which collapsed, causing earthquakes. 198 1 1 In some areas of Nankou Township, Yulin County, Guangxi Province, people heard the underground rumbling, and soon there was a collapse earthquake. In a few days, more than 200 places collapsed and some houses and fields were destroyed. The collapse earthquake has little influence and harm, accounting for only about 3% of the total number of earthquakes.
Other earthquakes. Many human activities can also cause earthquakes. One is that human activities directly cause earthquakes, such as blasting, piling and the passing of heavy vehicles, which can make the ground vibrate. This kind of earthquake is called artificial earthquake. This kind of earthquake generally does not cause harm, but it has a great influence on those instruments and equipment that require high precision and stability. Therefore, when installing these instruments and equipment, we should try our best to eliminate the unfavorable factors of man-made earthquakes. There is also an earthquake caused or induced by human activities. For example, the huge impulse generated by underground nuclear tests can cause fault activity; Reservoirs can also cause earthquakes, because most reservoirs are built in canyons, and there are often faults underground. On the one hand, the reservoir impoundment increases the pressure of the crust there, and at the same time, water permeates into the fault zone, acting as a lubricant, reducing the friction between faults and making them easy to slide. 1962 The M6.4 earthquake that occurred shortly after the storage of Xinfengjiang Reservoir in Guangdong Province in March was one of the largest reservoir-induced earthquakes in the world.
No matter what kind of earthquake, there are certain rules to follow. Now that we know the causes of various earthquakes, we won't feel the mystery of earthquakes any more. Of course, because some earthquakes will do great harm to human beings, we must take them seriously.
Earthquake precursor
Under the action of in-situ stress, in the process of stress and strain gradually accumulating and strengthening, rock mass will cause a series of abnormal changes in physics, chemistry, biology and meteorology of the source and nearby materials. We call these abnormal changes related to earthquake preparation and occurrence as earthquake precursors (also called earthquake anomalies). It includes microscopic earthquake anomalies and macroscopic earthquake anomalies.
Macroscopic anomaly of (1) earthquake
Earthquake anomalies that can be directly perceived by human senses are called earthquake macroscopic anomalies. The manifestations of earthquake macro-anomalies are diverse and complex, with hundreds of kinds of anomalies and thousands of anomalies, which can be roughly divided into groundwater anomalies, biological anomalies, geoacoustic anomalies, geooptical anomalies, electromagnetic anomalies, meteorological anomalies and so on.
1, groundwater anomaly
Groundwater includes well water, spring water, etc. The main anomalies are turbidity, bubbling, flowering, temperature rise, discoloration, odor change, sudden rise, sudden drop, borehole deformation, sudden exhaustion or spewing of spring water, etc. People summed up the proverbs of well water changes before the earthquake:
Well water is a treasure, and earthquakes have precursors.
When it doesn't rain, the spring water is turbid, and when it dries, well water emerges.
The water level rises and falls, and flowers are bubbling.
Some change color, some change taste.
2. Biological abnormality
Some organs of many animals are particularly sensitive. They can know some disasters ahead of humans, such as jellyfish in the ocean can predict storms, mice can avoid mine disasters or harmful gases in advance, and so on. As for the organs of vision, hearing, touch, vibration and balance, which plays the main role and which plays the role of assisting judgment may be different for different animals. Physical and chemical changes (vibration, electricity, magnetism, meteorology, abnormal radon content in water, etc.). ) The accompanying earthquake can often stimulate some sensory organs of some animals and cause abnormal reactions. If the gravity of an area changes, some animals may be able to feel it through its balance organs; Some animals' hearing organs may be able to detect abnormal vibrations. Before the earthquake, the underground strata have been moving slowly day by day, showing a creeping state, and there is strong friction between fault planes, so some people think that there will be low-frequency sound waves on the friction fault planes, only a few to ten times per second, which is lower than human hearing. People need more than 20 sound waves per second to feel it, but animals don't. Very sensitive animals will be frightened when they feel this sound wave, resulting in abnormal phenomena such as winter snakes coming out of holes, fish jumping out of the water, pigs and cows jumping in circles, dogs barking and wolves growling. There are many kinds of animal anomalies, including large livestock, poultry, cave animals, hibernating animals, fish and so on. The abnormal situation of animals, people also have a few words to sum up well:
Animals have signs before earthquakes, so it is very important to prevent and treat them by groups.
Cattle, sheep, mules and horses don't enter the stables, and pigs don't eat dogs and bite people.
Ducks don't go into the water and make noise on the shore, but chickens fly up the tree and scream loudly.
The snake came out of the hole in the ice and snow, and the mouse ran with the mouse in its mouth.
The rabbit jumped and bumped, and the fish jumped into the water.
Bees are moving noisily, but pigeons are too scared to fly back to their nests.
Every household observes and reports any abnormal situation.
In addition, some plants also had abnormal reactions before the earthquake, such as germination, flowering, fruiting or large-scale withering, abnormal exuberance and so on.
3. Meteorological anomalies
People often describe earthquake prediction scientists and technicians as "managing the sky, the ground and the hollow", which is indeed reasonable. Before the earthquake, the weather often appeared abnormal. There are mainly sultry before the earthquake, anxiety and irritability, long drought without rain or heavy rain, yellow fog, dark sunshine, strange wind, hail in June and so on.
4. Abnormal ground sound
Geosound anomaly refers to the sound emitted underground before the earthquake. Its sound is as changeable as cannon and thunder, like the driving of heavy vehicles and the surge of strong winds. When an earthquake occurs, longitudinal waves radiate from the source and propagate along the ground, making the air vibrate and sound. Because of the high speed but weak potential of longitudinal wave, people only smell its sound, but don't feel it unconsciously until the arrival of shear wave. Therefore, there is often a record in the epicenter that "before every earthquake, the underground sound expands like gas, like boiling water in a tripod". If you are in the epicenter, you can often hear the sound of a magnitude 3 earthquake. 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 may have a good effect on earthquake prediction and prevention.
5, abnormal grounding light
Geophysical anomalies refer to the light emitted underground before the earthquake, which has various colors, such as silver blue, white purple, etc., which are rare in daily life, but mainly red and white; Its forms are also different, such as ribbon, sphere, column, diffusion and so on. Generally speaking, the earth's light appears in a wide range, mostly within a few hours to a few minutes before the earthquake and lasts for a few seconds. In China, colorful luminous phenomena appeared during and before the Haicheng, Longling, Tangshan and Songpan earthquakes. Terrestrial light is often accompanied by natural phenomena such as earthquakes, landslides, landslides, collapses, sand blasting, water spraying and air jetting, and often moves regularly along a fault zone or an area, and is synchronized with other macro and micro anomalies, and its causes are always closely related to crustal movement. And controlled by geological conditions and the state of the surface and atmosphere, it can cause different degrees of harm to people, animals and plants.
At present, all the geomagnetic anomaly reports we have are from a few seconds before the earthquake to 1 minute. Such as Haicheng earthquake, Lancang earthquake and Gengma earthquake, similar reports have been collected.
6. Abnormal ground gas
Geo-atmospheric anomaly refers to the fog generated underground before the earthquake, also known as geo-aerosol or geo-fog. This kind of fog, with white, black and yellow colors, sometimes colorless, often appears in the days to minutes before the earthquake, often accompanied by strange smell, sometimes accompanied by noise or high temperature.
7. Abnormal ground movement
Abnormal ground motion refers to the ground shaking before the earthquake. It is a well-known phenomenon that the ground vibrates violently during an earthquake. But before the earthquake, sometimes I feel the ground shaking. This kind of shaking is different from an earthquake, and it swings very slowly. Seismographs often can't record it, but many people can feel it. The most obvious ground motion anomaly occurred before the Haicheng earthquake of magnitude 7.3 on February 4th, 1975. From the end of February to the end of June, there were 65438+ anomalies in Dandong, Kuandian, Fengcheng, Shenyang and Xiuyan.
8. Abnormal grounding drum
The ground uplift anomaly refers to the uplift on the ground before the earthquake. 1973 About half a year before the magnitude 7.9 earthquake in Luhuo, Sichuan, a drum appeared on a lawn in Tuoba District, Ganzi County. It was shaped like an inverted iron pot, about 20 cm high, and cracks appeared intermittently around it. The swelling disappeared after a few days, and it was repeated many times until the earthquake occurred.
Anomalies similar to ground heave include ground fissures and subsidence.
9. Electromagnetic anomalies
Electromagnetic anomalies refer to the anomalies of household appliances such as radios, televisions and fluorescent lamps before the earthquake. The most common electromagnetic anomaly is radio failure, and fluorescent lamps were also common before the North China earthquake. 1a few days before the Tangshan earthquake of magnitude 7.8 on July 28, 976, many radios in Tangshan and its surrounding areas broke down, with loud and small sounds, inaccurate frequency modulation and sometimes continuous noise. Also before the Tangshan earthquake, some people in the city saw fluorescent lamps turn red first and then light up at night. Some people in Beijing turn off the fluorescent lamp before going to bed, but the light is still on.
Electromagnetic anomalies also include abnormal operation of some motor equipment, such as abnormal microwave stations, interference from wireless power plants, and failure of electronic alarm clocks.
Macroscopic anomalies of earthquakes play an important role in earthquake prediction, especially in short-term and imminent prediction. Before the 1975 Haicheng M = 7.3 earthquake and the 1976 Songpan and Pingwu M = 7.2 earthquakes, seismologists and the general public had observed a large number of macroscopic anomalies, which provided important information for the successful prediction of these two earthquakes. However, it should also be noted that the above macro phenomena may be caused by various reasons, not all of which are signs of earthquakes. For example, the fluctuation of well water and spring water may be related to rainfall, and may also be affected by nearby pumping, drainage and construction. The discoloration and odor of well water may be caused by pollution, and the abnormal behavior of animals may be related to weather changes, diseases, estrus and external stimuli. Also be careful not to mistake welding arc light and lightning for earth light, thunder for earth sound, and fireworks and flares for underground fireballs.
Once you find an abnormal natural phenomenon, don't easily draw the conclusion that an earthquake is about to happen, let alone panic. Instead, it is necessary to find out the time, place and relevant situation of abnormal phenomena, protect the site, report to the government or the earthquake department, and let the professionals in the earthquake department investigate and verify to find out the truth.
(2) Microscopic anomalies of earthquakes
The seismic anomalies that can't be detected by human senses and can only be measured by special instruments are called microscopic anomalies of earthquakes, which mainly include the following categories:
Abnormal seismic activity: there is a certain relationship between large and small earthquakes. Although there are not many major earthquakes, there are many small and medium-sized earthquakes. Study the characteristics of moderate and small earthquakes. It is possible to help people predict the occurrence of future major earthquakes.
Abnormal topographic changes: Before the earthquake, the crust near the epicenter may be slightly deformed, and the rocks on both sides of some faults may be slightly displaced. With the help of precision instruments, this very weak change can be detected, and analyzing these data can help people predict the occurrence of future major earthquakes.
Geophysical changes: In the process of earthquake preparation, some changes may occur in the physical properties of rocks around the source area. Using precision instruments to measure the changes of gravity, geoelectricity and geomagnetism in different areas can also help people predict earthquakes.
Changes of underground fluids: Groundwater (well water, spring water, water contained in underground rock formations), oil and natural gas, and other gases may be generated and stored in underground rock formations, all of which are underground fluids. Using instruments to measure the chemical composition and some physical quantities of underground fluid and study their changes can help people predict earthquakes.