Earthquake, what is an earthquake

Earthquake , also known as ground motion and ground vibration, is a natural phenomenon in which vibrations occur during the rapid release of energy from the earth's crust and seismic waves are generated during the process.

Technology definitions Chinese name: Earthquake English name: earthquake Definition: Under the action of the earth's inner and outer forces, the tectonic stress of agglomeration is suddenly released, resulting in vibrating elastic waves, and terrible ground shaking caused by propagation from the source. Applied sciences: Water science and technology (a subject); Water conservancy survey, engineering geology (two subjects); Engineering geology (water conservancy) (three subjects)

Earthquake precursor

Precursors indicate abnormal phenomena that occurred before the earthquake, including well water and spring water. The main abnormalities are hair blisters, bubbling, turning flowers, warming, discoloration, bad taste, sudden rise, sudden descent, wellbore deformation, sudden spring depletion or gushing. People have summarized the proverbial well water change idiom: Well water is a treasure, and the earthquake has precursors. There is no rain springs, and the wells are running dry. The water level rises and falls, turning the flowers to take a bubble. Some change color, some taste. Many organs of many animals feel particularly sensitive. They can know in advance that some disaster events occur more than humans. For example, jellyfish in the ocean can predict storms; rats can avoid the collapse of mines in advance, and so on. As far as the visual, auditory, tactile, vibratory, and balanced organs are concerned, which have played a major role and which have played an auxiliary role, it may be different for different animals. The physical and chemical changes (vibration, electrical, magnetic, meteorological, anomaly, etc.) that accompany earthquakes can often cause certain sensory organs of some animals to become irritated and respond abnormally. Prior to the earthquake, animal response animals showed abnormal performances. Bulls, horses, donkeys, quailers panicked, did not enter the crickets, did not eat, chaos, gang fights, break the reins, slammed the ground, planed the ground, and suddenly trembled while walking. scale

At present, there are two major magnitudes and intensities for measuring the scale of earthquakes.

Earthquake phenomenon

When the earthquake occurs, the most basic phenomenon is the continuous vibration of the ground. The main feature is obvious shaking. People in the extremely earthquake zone sometimes feel up and down before they feel the big shaking. This is because seismic waves come from the ground to the ground and the longitudinal waves arrive first. The transverse wave then produces large-amplitude horizontal shaking, which is a major cause of earthquake disasters. When the Chilean earthquake struck in 1960, the maximum shaking lasted for 3 minutes. The disaster caused by the earthquake was the destruction of houses and buildings. For example, in the Tangshan earthquake in Hebei Province in 1976, 70% to 80% of the buildings collapsed, resulting in heavy casualties. The earthquake also has a great influence on the natural landscape. The main consequence is the faults and earthquake cracks on the ground. The surface faults of large earthquakes often stretch for tens to hundreds of kilometers, often with obvious vertical offset and horizontal offset, which can reflect the characteristics of structural changes at the source (see the Nengwei earthquake, the San Francisco earthquake). However, not all surface faults are directly related to the motion of the source. They may also be due to the secondary effects of seismic waves. Especially in areas with thicker surface sedimentary layers, ground fissures often occur along the slope, banks, and roads. This is often due to topographic factors. Looseness and cracking of topsoil are caused by shaking under conditions that do not rely on one side. The shaking of the earthquake caused the topsoil to sink, and the shallow groundwater was squeezed to rise along the ground fissures to the surface, resulting in sandblasting and watering. Large earthquakes can make local terrain change, or uplift, or settlement. The urban and rural roads were chapped, the rails were twisted, and the bridges were broken. In modern cities, due to the rupture of underground pipelines and the cut-off of cables, water cuts, power outages and communications were blocked. Leakage of gas, toxic gases, and radioactive materials can cause secondary disasters such as fires, poisons, and radioactive contamination. In the mountains, the earthquake can also cause landslides and landslides, often causing catastrophes in the villages and towns. The collapsed rocks clog rivers and form an earthquake lake upstream.

Earthquake distribution

Time Distribution 08-08-31 World Earthquake Situation

Seismic activity has a certain periodicity in time. The performance is that the seismic activity is frequent and the intensity is large during a certain period of time, which is called the active period of the earthquake. In the other time period, the seismic activity is relatively low and the intensity is small, which is called the quiet period of the earthquake.

related information

An earthquake is a seismic wave generated by a sharp rupture inside the Earth and causes ground vibration within a certain range. Earthquake is the rapid vibration of the Earth's surface. It was also known as earth motion in ancient times. It is like a tsunami, tornado, or frozen disaster

This is a kind of natural disaster that often happens on the earth. Earthquake vibration is the most intuitive and common manifestation of earthquakes. A strong earthquake that occurs on the sea floor or in the coastal area can cause huge waves, called tsunami. Earthquakes are extremely frequent and occur globally every year

The shock was about 500,000 times. Global plate movement earthquakes often cause serious casualties, can cause fires, floods, leakage of toxic gases, bacteria and radioactive material, and may also cause secondary disasters such as tsunami, landslides, collapses, and ground fissures.

Earthquakes have a certain spatial and temporal distribution.

From a time point of view, the earthquake has a periodic phenomenon in which the active period and the quiet period alternate. From a spatial point of view, the distribution of earthquakes is a certain band, called the seismic zone. As far as continental earthquakes are concerned, they are mainly concentrated in

The Pingyang Seismic Belt and the two major seismic belts of the Mediterranean-Himalayan seismic zone. The Pacific Seismic Belt has concentrated nearly 80% of shallow earthquakes (0 km to 60 km) in the world, all of the medium (60 km to 300 km) and deep-sourced earthquakes (>300 km).

The seismic energy released accounts for about 80% of the total energy.

Earth can be divided into three layers. The central layer is the core of the earth, the core is mainly composed of iron elements; the middle is the mantle; the outer layer is the crust. Earthquakes usually occur in the earth's crust. The interior of the earth's crust is constantly changing. As a result, the force (that is, the internal force) acts to deform, fracture, and move the earth's crust and rock. Thus, an earthquake occurs. Super earthquakes refer to earthquakes with extremely strong earthquake waves. However, its occurrence accounted for 7% to 21% of the total earthquake, and the damage was several times that of the atomic bomb. Therefore, the super earthquake has a wide range of impact and is very destructive.

Destructive earthquakes are generally shallow earthquakes. For example, the source depth of the 1976 Tangshan earthquake was 12 km. The most violent ground vibrations of a destructive earthquake are called extreme earthquake zones, and the extremely seismic zone is often the area where the epicenter is located.

The distance from the epicenter to the observation point is called the epicentral distance. Earthquakes less than 100 kilometers away from the epicenter are called local earthquakes, earthquakes between 100-1000 kilometers are called near-earthquakes, and earthquakes larger than 1000 kilometers are called far-field earthquakes, where the longer the epicenter distance is affected and destroyed. small.

Earthquake-induced ground vibration is a complex movement that is the result of the combination of longitudinal and transverse waves. In the epicentral area, longitudinal waves make the ground up and down. The transverse wave shakes the ground horizontally. As the longitudinal wave propagation speed is faster, the attenuation is also faster, and the transverse wave propagation speed is slower.

The reduction is also slower. Therefore, the place far away from the epicenter is often not felt to jump up and down, but it can feel horizontal shaking. When a large earthquake occurs in a certain place, a series of earthquakes tend to occur over a period of time. The largest earthquake is called the main shock. The earthquake that precedes the main shock is called the foreshock. The earthquake that occurred after the main shock is called aftershock.

The place where the underground rock breaks and shifts originates is called the focus. The vertical projection of the source on the ground, and the point closest to the source on the ground is known as the volcanic belt distribution of the Earthquake in China. It is the site of the earliest vibration. The depth from the epicenter to the source is called the focal depth. The shallow source earthquake with a depth of less than 60 kilometers, the Zhongyuan earthquake with a depth of 60-300 kilometers, and the deep-sourced earthquake with a depth of more than 300 kilometers are usually used. For earthquakes of the same size, the damage to the ground is not the same due to the different focal depths. The shallower the source, the greater the damage, but the smaller the extent of the spread, and vice versa.