The various signs that occur in nature before an earthquake that may be related to the conception and occurrence of an earthquake are called earthquake precursors. There are two broad categories.

Microscopic precursors: Pre-earthquake changes that are not easily perceived by the human senses and can only be measured with instruments. For example, deformation of the ground, changes in the earth's magnetic and gravitational fields, changes in the chemical composition of groundwater, and the activity of small earthquakes.

Macroscopic precursors: Earthquake precursors that can be perceived by the human senses. They mostly appear near the time of earthquake. For example, the rise and fall of well water, muddy, animal behavior abnormalities, ground sound and light, etc.

Groundwater anomalies

① water level, the amount of paradoxical changes. Such as dry season well water level rose, the spring water increased; water level in the season of abundance but fell or spring break. Sometimes there is also a well water self-flow, self-jet and other phenomena.

② changes in water quality. Such as well water, spring water, such as discoloration, taste (such as bitter, sweet), muddy, odor, etc..

③ changes in water temperature. Water temperature exceeds the normal range of variation.

④Other. Such as flopping and bubbling, spewing and rattling, well wall deformation, etc.

Biological anomalies

Animals are "living instruments" for observing earthquake precursors, and they often show various abnormal behaviors before the earthquake to foretell people of the approaching disaster. Hundreds of animals have been found to behave abnormally before earthquakes, of which more than 20 kinds of abnormal reactions are more common.

Panic reaction: such as large livestock do not enter the pen, dogs barking, birds or insects flying in fear, abnormal group migration, etc.

Inhibition-type abnormalities: such as behavior becomes slow, or dazed and dumb, do not know what to do; or refuse to eat, etc.

Changes in living habits: such as hibernating snakes coming out of their holes, rats moving during the day without fear of people, large numbers of frogs moving ashore, etc.

Electromagnetic anomaly

Electromagnetic anomalies refer to the malfunction of household appliances such as radios, televisions, fluorescent lights, etc. before an earthquake. The most common phenomena are the failure of the radio, the weakening or disappearance of cell phone signals, and the failure of electronic alarm clocks.

Ground sound

Before an earthquake, there is often a sound coming from deep underground, which is called "ground sound". The sound of the earth usually appears a few minutes, hours, days or earlier before the earthquake; the most frequent is a few minutes before the earthquake.

The sound of the earth is different and diverse from the familiar sounds. For example: "like a train coming from underground", "like a rock quarry with a series of cannons", "similar to the roar of a machine", "the roar of the wind". " "the sound of stones rubbing against each other" and so on. However, sometimes the sound of the ground is not easy to identify with the sound of wind, thunder, machine roar, etc. from afar.

Ground light

Ground light is also a macroscopic phenomenon before earthquakes, and has been observed in China before many earthquakes, they usually appear before or during the earthquake, but also a few hours before the earthquake or earlier.

The ground light has many colors, including red, yellow, blue, white, and purple, and some of them also look like electric firelight. They have different shapes, such as band light, sheet light, spherical light, column light, fire-like light, etc. The appearance of the ground light is generally very short, so it is not easy to observe. Identifying ground light is also difficult because its shape and color sometimes have similarities with welding light and lightning.

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