What are the common precursors of earthquakes?

Under the action of geostress, in the process of stress and strain gradually accumulating and strengthening, rock mass will cause a series of abnormal changes in physical, chemical, biological, meteorological and other substances around the source. We call these abnormal changes related to the preparation and occurrence of earthquakes as earthquake precursors (also known as earthquake anomalies), which include two categories: earthquake microscopic anomalies and earthquake macroscopic anomalies.

Macroscopic anomaly of (1) earthquake

Earthquake anomalies that can be directly perceived by human senses are called earthquake macro-anomalies. The manifestations of earthquake macro-anomalies are diverse and complex, with hundreds and thousands of kinds 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, off-flavor, sudden rise, sudden drop, borehole deformation, sudden exhaustion or gushing of springs, 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. For example, jellyfish in the ocean can predict storms, and rats can avoid mine collapses or harmful gases in advance. As for vision, hearing, touch, vibration and sense of balance, which organs play a major role in judgment and which play an auxiliary role 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. For example, if the gravity of an area changes, some animals may be able to feel it through their balance organs; Abnormal vibration that may be detected by the auditory organs of some animals. Before the earthquake, the underground rock strata have been moving slowly day by day, showing a state of peristalsis, and there is strong friction between fault planes, so some people think that low-frequency sound waves will be generated on the friction fault planes only a few to ten times per second, which is lower than human hearing. People have to feel it at a speed of more than 20 times per second. On the other hand, animals are not. Animals that feel very sensitive will be terrified when they feel this sound wave, resulting in abnormal phenomena such as snakes coming out of holes, fish jumping out of the water, pigs and cows jumping in circles, dogs crying and wolves growling in winter. There are many kinds of animal anomalies, including large livestock, poultry, cave animals, hibernating animals, fish and so on. People also have a few words to summarize the abnormal situation of animals:

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 go back to their nests.

Every household observes and reports any abnormality.

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 technicians as "the sky above, the ground below and the air in the middle", which makes sense. Meteorological anomalies often occur before earthquakes, mainly including sweltering heat before earthquakes, people's anxiety and irritability, persistent drought or heavy rain, yellow fog and fog, dim sunshine, strange wind and hail in June, etc.

4. Abnormal ground sound

Abnormal ground sound refers to the sound from underground before the earthquake. Its sound is as varied as the thunder of a cannon, the running sound of a heavy car and the ups and downs of a strong wind. When an earthquake occurs, longitudinal waves radiate from the source and spread along the ground, making the air vibrate and sound. Because of the high speed but weak potential of longitudinal wave, people only smell the sound, but can't feel the ground moving. Therefore, the epicenter often has the feeling that "there is a shear wave before every earthquake". For example, it is recorded that boiling water expands in a tripod. Earthquakes of magnitude 3 are often heard in the epicenter. Earthquakes are the result of the structural changes of underground rocks and the movement of liquids and gases contained in them, and a considerable part of them are signs of impending earthquakes. Mastering earthquake knowledge 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, dispersion and so on. Generally, ground light appears in a wide range, mostly within a few hours to a few minutes before the earthquake and lasts for a few seconds. China Haicheng, Longling, Tangshan, Songpan and other places have colorful luminous phenomena during and before the earthquake. Ground light is usually accompanied by natural phenomena, such as earthquakes, landslides, collapses, sand blasting and spraying. It is synchronous with other macro and micro anomalies, and its cause is always closely related to crustal movement. It is also controlled by geological conditions and the state of the surface and atmosphere, which can cause different degrees of harm to people, animals and plants.

At present, the geomagnetic anomaly reports we have are all from a few seconds before the earthquake to 1 minute, such as Haicheng earthquake, Lancang earthquake and Gengma earthquake.

6. Abnormal ground gas

Geo-atmospheric anomaly refers to the fog from underground before the earthquake, also known as geo-atmospheric aerosol or geo-fog. This kind of fog, with white, black, yellow and other colors, sometimes colorless, often appears within a few days to a few minutes before the earthquake, often accompanied by strange smell, sometimes accompanied by sound or high temperature.

7. Abnormal ground movement

Abnormal ground motion refers to the ground vibration before the earthquake. It is a well-known phenomenon that the ground vibrates violently during an earthquake. However, before an earthquake, the ground sometimes feels shaking. This kind of shaking is different from that during the earthquake. The shaking is very slow, which is often not recorded by seismographs, but many people can feel it. The most obvious ground motion anomaly occurred before1February 4, 975 Haicheng earthquake with M = 7.3. 1974 to 1975 10, an earthquake of magnitude 17 occurred in Dandong, Kuandian, Fengcheng, Shenyang and Xiuyan.

8. Abnormal grounding drum

The ground drum anomaly refers to the uplift on the ground before the earthquake. About half a year before the earthquake of magnitude 7.9 in Luhuo, Sichuan, a ground 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. After a few days of swelling, it disappeared and repeated several 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 in northern areas before the earthquake. A few days before the Tangshan earthquake of magnitude 7.8 on July 28, 1976, many radios in Tangshan and its surrounding areas broke down, with loud voices, inaccurate frequency modulation and sometimes continuous noise. Similarly, before the Tangshan earthquake, many radio stations in Tangshan and its surrounding areas failed.

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 earthquake with M = 7.3 and the 1976 Songpan and Pingwu earthquakes with M = 7.2, seismologists and the masses had observed a large number of macroscopic anomalies, which provided important information for the successful prediction of these two earthquakes. However, we should also see that the macro phenomena listed above may be caused by various reasons. 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 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 ground light, thunder for ground sound, and fireworks and flares for underground emission.

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. Studying the characteristics of small and medium-sized earthquakes may help people predict the occurrence of future major earthquakes.

Topographic anomaly: 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 some other gases may be generated and stored in underground rock formations. These are underground fluids. Measuring the chemical composition and some physical quantities of underground fluid with instruments and studying their changes can help people predict earthquakes.

1. Macroscopic precursors of earthquakes

People's senses can directly perceive earthquake precursors, referred to as macro precursors. The common ones are the sudden rise and fall of well water, discoloration and odor change, flowering and bubbling, temperature fluctuation, sudden change of spring water flow, sudden change of hot spring water temperature, abnormal animal behavior, ground sound and ground light before the earthquake, etc.

Macroscopic precursors play an important role in earthquake prediction. Before the 1975 Haicheng earthquake with M = 7.3 and the 1976 Songpan-Pingwu earthquake with M = 7.2, seismologists and the masses had observed a large number of macroscopic anomalies, which provided important information for the successful prediction of these two earthquakes. However, we should also pay attention to the various macro phenomena listed above, which may be caused by various reasons and are not necessarily precursors of earthquakes. The group 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 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 jump to the conclusion that an earthquake will happen soon, 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 earthquake department or the government, and let the professionals in the earthquake department investigate and verify the truth.

2. Microscopic precursors of earthquakes

Earthquake precursors that can't be detected by human senses and can only be measured by special instruments are called earthquake microscopic precursors, which mainly include the following categories:

The earthquake activity is abnormal. 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. Studying the characteristics of small and medium-sized earthquakes may help people predict the occurrence of future major earthquakes.

Abnormal topographic deformation. 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, the physical properties of rocks in and around the source area may change. Using precision instruments to measure the changes of gravity, geoelectricity and geomagnetism in different areas can also help people predict earthquakes.

Changes of underground fluid. Groundwater (well water, spring water, water in underground rocks), oil and natural gas and other gases may be produced and stored in underground rocks. These are underground fluids. Measuring the chemical composition and some physical quantities of underground fluid with instruments and studying their changes can help people predict earthquakes.

Judging from people's feelings in Tangshan and other earthquake areas, there is generally about ten seconds' warning time from the occurrence of an earthquake to the destruction of houses. The early warning phenomena of major earthquakes mainly include: ground motion, ground sound, ground light, building shaking and so on.

Groundwater:

When the rock stratum is deformed, the state of the underground aquifer will also change, so the groundwater will often produce some abnormal phenomena: the well water is bubbled like a flower, rising and falling suddenly, and it will be turbid without rain, and its color will change and its smell will be unpleasant. However, groundwater is easily affected by the environment, so don't be alarmed if it is abnormal, and report it to the earthquake department first.

The weather is dry, the well is flooded, and there are abnormal ups and downs.

Without rain, it becomes muddy, discolored and stinks.

The jet plane rang again and the flowers were in bloom.

Animal abnormality:

Many earthquake examples show that animals often behave abnormally before earthquakes. The following is a ballad about animal precursors before the earthquake:

Animals have precursors before earthquakes and report any abnormalities.

Cattle, horses, mules and sheep don't enter the circle, 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 got out of the hole in the ice and snow, and the mouse moved away stupidly.

The rabbit jumped and bumped, and the fish jumped in panic.

Bees move noisily, but pigeons fly back to their nests in fear.

The voice of the earth is strong and strange.

The ground lamp is horribly bright.

Ground sound and ground lighting:

Before and during the impending earthquake, ground sound and ground light often appear together. The sound on the ground is similar to the roar of machines, thunder, guns and the roar of strong winds. Ground light has various colors and shapes, such as ribbon, sheet, sphere, column and fire-like light.