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Common Knowledge of Earthquake

The earthquake is the rapid vibration of the surface of the earth. It was also called the earth motion in ancient times. It is a natural phenomenon that often occurs on the earth, just like wind, rain, lightning, landslide and eruption of volcanoes. There are many causes of the vibration of the surface of the earth. According to the cause of the earthquake, the earthquake can be divided into tectonic earthquake, volcanic earthquake, collapse earthquake, induced earthquake and man-made earthquake.

Seismic precursors

For the abnormal phenomena related to the earthquake that occur in nature before the earthquake, we call them the seismic precursors, which include two major types of microscopic precursors and macroscopic precursors. The common seismic precursor phenomena are: (1) abnormal  seismic activities; (2) changes in the velocity of seismic waves; (3) crustal deformation; (4) abnormal changes in underground water; (5) changes in radon gas content or other chemical components in underground water; (6) changes in crustal stress; (7) changes in geologic electricity; (8) changes in geomagnetism; (9) gravity anomaly; (10)  animal anomaly; (11) earthquake sounds; (12) earthquake light; (13) geothermal anomaly and so on. Of course, the above-mentioned anomalies are very complex and are often not necessarily caused by the earthquakes. For example, the fluctuation of the underground water level is related to rainfall, drought, man-made pumping and irrigation. Also, animal anomaly is often related to the changes in weather, rearing conditions change, living conditions, the physiological status of the animals and so on. Therefore, we must firstly identify the reasons for these changes and then consider whether they are related to earthquake.

Main Abnormal Reaction of Animals before Earthquake

Before the occurrence of large earthquake, birds and animals, domestic animals, reptiles, cave animals and aquatic animals often show different degrees of abnormal reactions. The abnormal manifestation of animals before the occurrence of large earthquake includes emotional irritability and panic; or the animals will fly and jump high, run wildly and shout madly; or they will be dispirited and afraid to stay in its places and etc. The animals’ abnormal observation has certain significance to the earthquake prediction. People in earthquake region summarized the proverb like this: Animals have warnings before earthquake, people need to make the work of earthquake resistance and disaster prevention well. Cattle, sheep donkey and horse are afraid to enter their pens and mouse moves to other places and escape; chicken flies on the tree and pig breaks its pen door, duck is unwilling to enter the water and dog shouts madly; rabbit pricks up its ears, jumps and hit, dove is frightened to fly and afraid to back to its nest; snake during hibernation gets out of its hole early, fish is frightened to jump out of the water. Every family needs to observe the situation and combine the abnormal conditions for prediction.

Main Characteristics of Abnormal Reaction of Animals before Earthquake

(1) The time distribution of precursor for the occurrence of animals’ abnormal reactions: The time distribution of the abnormal reactions of a number of animals before earthquake mainly focuses on a few days before earthquake to a couple of hours before earthquake. (2) Characteristics of distribution for areas where animals have abnormal reactions before earthquake: Generally speaking, animals’ abnormal reaction range before an M 7 earthquake can reach one, two hundred and even hundreds of kilometers. The magnitude of earthquake is large, its abnormal distribution range is large as well; the magnitude of earthquake is smaller, its abnormal distribution range is smaller as well. (3) The relationship between the animals’ abnormal reactions before earthquake and the magnitude: with the increase in magnitude of earthquake, the species, quantity, distribution area and intensity for animals’ abnormal reaction are increased correspondingly. In general, individual animal will show an abnormality before about M 3 earthquake. The common animals will show more obvious abnormalities in a certain region before about M 5 earthquake. Many animals will show strong abnormalities in a large range of regions before about M7 violent earthquake. The relationship between animals’ abnormal reactions and intensity distribution is obvious. The regions with higher intensity will have greater amount of abnormal reaction.

Methods for Observation of Animals’ Abnormal Conditions

The key monitoring regions for earthquake activities and the places with quiet ambient environment and less interference and pollution should be chosen as the observation points for animal abnormalities. The observation points can be set up in the zoo and weather station where have feeding farms and livestock farms with a certain scale; it is best to jointly set up with other observational points with precursory means or close to the places of other observational points in order to facilitate comprehensive analysis of data. The selection for observed animals needs to pay attention to the convenience of source and economy; the common animals that can be easy to see and observe include house mouse, loach, catfish, snake, pigeon, parrot and horse, sheep, pig, dog, chicken and other poultries and domestic animals. The captive animals can be observed at fixed point and time and animals’ behaviors, water temperature, change of air pressure environment and so forth can be recorded as well. If the condition does not permit, they can be observed once in the morning, afternoon and evening or observed at any time and recorded in details. For wild animals, they can be observed routinely, namely once in the morning, afternoon and evening; various kinds of animals that can be seen, quantity and weather condition need to be recorded. The observation results should be reported and summarized regularly, time-space distribution graph should be drawn timely and the comprehensive analysis should be carried out as well.

Abnormal Phenomenon of Underground Water before Earthquake

Before the occurrence of large earthquake, underground aquifer is squeezed strongly in the structural change, which destroys the state of the aquifer near the earth's surface and makes the underground water redistribute, resulting in water level in some regions to rise and in other regions to drop. The change in chemical substance component in the water makes the taste and color of the underground water in some regions change, the water surface appear the floating “oil slick” and swirling and bubbling, etc. The pre-earthquake anomalies of underground water level and chemical composition of water is more obviously in the active fault and other surrounding areas and often more concentrated in the meizoseismal area. People in the disaster-hit regions often say that the well water is a treasure and has a precursor in advance. When it does not rain, the spring is muddy, when the weather is dry, the well water emits upward; the water level rises and waterfall greatly, the water bubbles; some changes color and some changes taste. If the weather changes, the rain will come and if the water changes, the earth surface will change.

Earth Sound before Earthquake

In most cases, there is earth sound to be produced from underground in a few hours to a few minutes before the occurrence of large earthquake, rarely in a few days before earthquake. Some sounds like “buzz” sound of the airplane, some sounds like the shrieking wind, some like passing cars, some likes a thunder muttering in the distance and some like mountain blasting and blast firing…the distribution of earth sound is very wide, which is more prominent in the high earthquake intensity regions. It can be said based on the experiences of people in disaster-hit areas that the magnitude of earthquake and the direction of epicenter can be judged according to the characteristics of the earth sound, “If large earthquake appears, the earth sound is deep and if small earthquake appears, the earth sound is high-pitched; if the earth sound is long, the earthquake is far away and if the sound is short, the earthquake is nearby.”

The phenomena in the nature that related to the earthquake generation before earthquake are called as earthquake precursor. In the long term practice, the ancient Chinese people began to know in the early time that there is a precursor before earthquake and they left rich records about earthquake precursor. For example, after the occurrence of earthquake in Yinchuan Ningxia in 1739, it had been concluded that there might be some connection between the earthquake and the change of well water, uneasiness of animals, underground sound before earthquake and abnormal phenomenon of weather.

The ancient book Longde County Annals recorded six earthquake precursor phenomena summarized by the ancients. The in-depth study of modern earthquake science shows that there really exist many kinds of precursor phenomena before earthquake. The earthquake precursor is divided into macroscopic precursor and microscopic precursor.

1. Macroscopic precursor of earthquake

The human's senses can be directly aware of the earthquake precursor, which is called as macroscopic precursor of earthquake and macroscopic precursor for short. The more commonly seen macroscopic precursor includes the steep rise and drop of well water, color and taste change, water bubbling, temperature rising and dropping, sudden change in flow capacity of spring, sudden change in temperature of spring, abnormal behaviors of animals and earth sound and light before earthquake, etc.

Macroscopic precursor plays an important role in earthquake prediction. Before the occurrence of M 7.3 earthquake in Haicheng County, Liaoning Province in 1975 and Songpan-Pingwu M 7.2 earthquake in 1976, the earthquake workers and the masses had observed a great number of macroscopic abnormal phenomena, providing the important data for the successful prediction of the two earthquakes. However, it should be noted that many kinds of macro macroscopic phenomena listed above may be caused by many reasons, not necessarily the earthquake precursor. For example, the small rise and drop in well water and spring may be related to the amount of rainfall and may be affected by the influences of nearby pumping, drainage and construction as well. The changes in color and taste of the well water maybe caused by the pollution and the animals’ abnormalities may be related to the weather change, disease, estrus and external stimulation, etc. It should also be noted that the welding arc and lightning and so forth cannot be mistaken for earth light, the thunder cannot be mistaken for earth sound as well as setting off of fireworks and firecrackers and signal flares cannot be taken as the fireball emitting from underground.

Once the abnormal natural phenomena are discovered, do not make a conclusion about the imminent earthquake easily, do not be panic but should find out the time, place and relevant circumstances of abnormal phenomena, preserve the site well and report to the Earthquake Department or the Government so that the professionals of the Earthquake Department can investigate, verify and find out the truth.

2. Microscopic precursor of earthquake

The human’s sense cannot perceive it, only the special equipment can measure the earthquake precursor, which can be called as the microscopic precursor of earthquake and microscopic precursor for short. It mainly includes the following several categories:

Abnormal earthquake activities. There is a certain relationship between large earthquakes and small earthquakes. Although there are not many large earthquakes, the medium-small earthquakes are quite a few. The research on the characteristics of medium-small earthquake activities may help people predict the occurrence of forthcoming large earthquakes.

Crustal deformation anomalies. Before the occurrence of a large earthquake, the crust in the region near the epicenter may show a tiny deformation, some rock stratum on both sides of the fault may appear a tiny displacement. This very weak change can be detected depending on the precise instrument. Analysis of these data can help people predict the occurrence of forthcoming large earthquakes.

Geophysical change. In the process of earthquake generation, some changes occur in the physical property of the source regions and its surrounding rocks. The precise instrument can be used to measure the changes of gravity, earth electricity and geomagnetism at different regions, which can help people predict the earthquakes.

Changes of underground fluids. Some other gases may be produced and stored in the underground water (well water, spring, water contained in the underground layer), petroleum and natural gas and underground rock stratum, which can be called underground fluids. The chemical components and some physical quantity of underground fluids can be measured by the instrument and the research on their changes can help people predict the earthquakes.

3. Earthquake observation network

In order to capture the microscopic precursor of earthquake, it is necessary to establish the earthquake observation network covering areas and carry out a long time precise observation.

The instrument that records the earthquakes is called as the seismograph. The station that specializes in seismological observation is called as the seismostation or instrument measurement table. Over 1800 years ago, China’s famous scientist Zhang Heng had invented the world’s first seismograph-“Houfeng Seismograph”. The modern seismograph has adopted the most advanced electronic technology, has a higher sensitivity and even has specific sea seismograph and deep well (borehole) seismograph. Currently, a considerable part of seismograph stations can automatically record the earthquake signal without appointing the special person to observe, transmit the signal automatically to the receiving center through cable or radio wave and be processed automatically by the computer, which is called as the telemetered seismic network. Including Sichuan Province, many regions of our country have established a modern telemetered seismic network. In addition, many regions of our country have established the observation stations for earth electricity, geomagnetism, gravity, crustal deformation, underground fluids and other earthquake precursors.

Before liberation, in old China, there was only one seismostation and three earthquake workers. The earthquake undertakings at that time were very backward. After liberation, the undertakings in New China have been greatly developed. In 1957, the first seismostation of Sichuan Province, namely Chengdu Seismostation, was established in the western suburbs of Chengdu. After Xingtai earthquake in 1966, under the loving care of Premier Zhou Enlai, China’s earthquake undertakings had accelerated its development paces. In 1971, China had established the State Seismological Bureau (now it is called China Seismological Bureau). After nearly 30 years of tremendous efforts, earthquake observation network has developed to a certain scale and currently China has set up more than 1000 modern seismostations (including local seismostation). In addition, earthquake observation technology has been widely applied to electronic, radio transmission and digitized and other high and new technologies.

Ministry of Land and Resources P.R. ChinaDepartment of Land and Resources of Hubei ProvincePeople’s Government of HuanggangHuanggang Municipal Bureau of Land and ResourcesGlobal Geoparks NetworkNational Geopark of China The Geological Museum of ChinaHong Kong UNESCO Global GeoparkShennongjia Global GeoparkTianzhushan Global Geopark

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