Earth can be divided into three tiers. Center is the core layer; mantle is in the middle; is the outer crust. Earthquake occurred in the earth's crust in general. Crust kept in the internal changes resulting from this force, so that the crust of rock deformation, fracture, dislocation, and then the earthquake.
Earth's interior is a medium earthquake occurred in a sharp break down, resulting seismic waves, which caused a certain range of vibration on the ground. Seismic (earthquake) is the rapid vibration of the earth's surface, also known as the earthquake in the ancient times. It is like wind, rain, lightning, like the earth is often a natural phenomenon. Vibration of the earth quake was the most intuitive, the most common. Or seabed in the coastal areas of strong earthquakes can cause huge waves known as tsunamis. Earthquakes are very frequent, the world's earthquakes each year around 500 million
Origin of seismic waves, known as the source (focus). Source on the ground in a vertical projection, on the ground from the nearest point source known as the epicenter. It is the vibration of the first to accept the position. To the epicenter of the focal depth of the focal depth is called. Focal depth will be generally less than 70 km of shallow earthquakes called, in the depth of 70-300 km in the name of the source of the earthquake, the depth is greater than 300 km deep source called the earthquake. For the same size of the earthquake, as the focal depth is not the same as on the ground nor the extent of the damage caused by the same. The more shallow source, the greater the damage, but also affected the smaller the range, and vice versa.
Destructive earthquakes are shallow earthquakes. If the 1976 Tangshan earthquake as the focal depth of 12 km.
The devastating earthquake ground vibration of the Department known as a very strong earthquake zone, the area very often that is where the epicenter of the region.
With an epicenter distance call away from the epicenter. Less than 100 km from the epicenter of the earthquake known as the local earthquake in the 100-1000 km between the earthquake as the recent earthquake, more than 1000 kilometers of the earthquake far as the earthquake, in which, the farther away from the epicenter of the impact on local and The smaller the damage.
Earthquake caused by the vibration of the ground is a complex exercise, it is by the P-wave and the wave together. In the epicentral, on the ground so that the wave moving up and down Britain. So that the wave shaking the ground level. As the wave spread faster, also decay faster, slower S-wave velocity, and also decay slowly, so far away from the epicenter, often do not feel beat up and down, but the level was shaking.
When a place of a large earthquake, for a period of time, usually a series of earthquakes, one of the largest earthquake known as the main shock, the main shock before the earthquake is called before the earthquake, which occurred after the main shock is called the earthquake aftershocks .
Earthquake with a certain amount of time and space distribution.
From the time point of view, there is an earthquake active and quiet periods alternating cyclical phenomenon.
From space, the distribution of the earthquake was a certain band, said the seismic zone, mainly in the Pacific Rim and the Mediterranean - the two major Himalayan seismic zone. Pacific seismic belt in the world to focus almost 80% of the shallow earthquakes (0 km to 70 km), all of the source (70 km to 300 km) and deep-source earthquakes, the seismic energy released about 80% of the total energy.
Magnitude
Magnitude refers to the size of the quake, characterization is a measure of the strength of the earthquake, an earthquake is to measure seismic activity in each of the energy released to determine how much of. The magnitude is usually indicated by the letters M. At present, China's use of the standard magnitude, the international community is a common grade on the Richter scale grades is divided into 9. Usually less than the 2.5 earthquake earthquake Jiaoxiao ,2.5-4 .7 called Earthquake felt tremors greater than 4.7 earthquake known as the devastating earthquake. Magnitude 1.0 per difference, a difference of about 30 times the energy; every difference of 2.0, a difference of about 900 times more energy. For example, a 6-magnitude earthquake released energy equivalent to the United States dropped the atomic bomb in Hiroshima, Japan, with the energy. 7 earthquake is equivalent to a 32 6 earthquakes, or the equivalent of 1,000 5 earthquake
According to the size of the magnitude of the earthquake can be divided into the following categories:
Weak local earthquake magnitude is less than 3. Felt the earthquake magnitude equal to or greater than 3 and less than or equal to 4.5.
In the earthquake greater than magnitude 4.5, less than 6. Magnitude earthquake is equal to or greater than 6. One of magnitude greater than or equal to 8, also known as the great earthquake.
Seismic intensity
Similarly, the size of the earthquake, the damage caused is not necessarily the same; with an earthquake, the difference in damage caused is not the same. In order to measure the extent of earthquake damage, scientists and "production" to a "ruler" one by one seismic intensity. Intensity Earthquake in China, people's feelings, the general level of housing damage and other phenomena described can be used as the basis for determining intensity. There are factors that affect the intensity of the magnitude, depth and distance from the epicenter, the ground state of formation and structure, and so on.
Under normal circumstances, only the source and intensity, the relationship between the magnitude, the greater the magnitude of the more shallow focus, greater intensity. In general, the first time after the earthquake, the epicentral the heaviest damage, the highest intensity; the intensity as the intensity of the epicenter. From around the epicenter to the expansion of seismic intensity gradually decreased. Therefore, there is only one magnitude of an earthquake, but it caused damage in different areas are different. In other words, an earthquake can be divided into several different intensity. This is a bomb explosion, near and far different from the degree of damage to the same reason. The amount of explosives, bombs, is like a magnitude; bombs at various locations on the extent of the damage, the intensity is like.
For example, on February 10, 1990, Changshu - Taicang 5.1 earthquake occurred, said it was in Suzhou is a 4, 3 in Wuxi is that this is wrong. Regardless of where they are, can only say that the Changshu - Taicang 5.1 earthquake occurred, but the earthquake in the sand Town, Taicang seismic intensity of 6 degrees in Suzhou is a seismic intensity of 4 degrees in Wuxi seismic intensity is 3 degrees.
In countries around the world have used several different Intensity. Western countries is to improve the passage of time Maijialilie table, referred to as MM Intensity, from time to time I will be divided into 12 intensity level. Japan will not feel as 0 degrees, I felt it to be divided into Ⅶ, a total of 8 grades. The former Soviet Union and China are divided into 12 intensity level Intensity. China in 1980 to redesign the form of seismic intensity (see table).
China Earthquake Intensity
1 degrees; no sense - can only instruments recorded;
2 degrees; micro-felt - a particularly sensitive one in Sino-felt completely static;
3 degrees; little sense - a small number of people in the room felt in a static, a slight swing Xuangua Wu;
4 degrees; more felt - most of the indoor and outdoor small number of people felt, Xuangua Wu swing, sound unstable containers;
5 degrees; awakened - the majority of people felt outdoors, restless animal, creaking doors and windows, wall cracks on the surface
6 degrees; panic - people standing instability in the flight of domestic animals, utensils Fan Luo, simple hut damage, landslide scarp;
7 degrees; damage to housing - housing minor damage, of St. Paul, damaged chimneys, cracks and surface water run sandblast;
8 degrees; damage to buildings - many housing damage, damage to a small number of road cave-in, underground pipeline rupture;
9 degrees; widespread destruction of buildings - most of the damage to housing, a small number of dumping, of St. Paul, such as the chimney collapsed, bending the tracks;
10 degrees; widespread destruction of buildings - the dumping of housing, roads destroyed and a large number of rocks collapsed, the water head-shore big wave;
11 degrees; destruction - the collapse of a large number of housing, road embankment collapse large, significant changes in the surface;
12 degrees; Yi Jing mountains and rivers - all destroyed buildings, dramatic changes in the terrain of animals and plants has been destroyed;
For example, the 1976 Tangshan earthquake, magnitude 7.8 to, the epicenter for the intensity of 11 degrees; by the Tangshan earthquake, seismic intensity for eight Tianjin, Beijing intensity for six, and then to the far Shijiazhuang, Taiyuan, and so on, only 4-5 The degree.
Seismic phenomena
An earthquake occurs, the most basic is a row of ground vibration, the shaking is obvious.
Most people in the earthquake zone was a big rock before the first is sometimes beat up and down. This is because the seismic waves from the ground came to that first wave arrived because. Then have a big wave amplitude of the shaking of the horizontal direction is the main reason for disasters caused by earthquakes. 1960 Chile earthquake, the biggest shaking lasted for 3 minutes. First of all, the earthquake disaster was caused by the destruction of homes and structures, such as the 1976 Tangshan earthquake in China, 70% to 80% of the buildings collapsed, suffered heavy casualties.
Seismic nature of the landscape have a significant impact. The most important consequence of a disruption on the ground and cracks. The earthquake fault surface often stretching to several dozens of kilometers, often with obvious from the mistake and the level of vertical distance wrong, to reflect the epicenter of the tectonic changes in the characteristics of the Department (see the end of strong earthquake, the San Francisco earthquake). However, not all the fault surface and the source directly linked to the movement, they also may be due to seismic waves caused by secondary impact. In particular, the surface area of thick sediment, the sloping edge of the road on both sides of the river bank and often to crack, which is often due to the terrain, in the side of not relying on the conditions so that the shaking loose topsoil and crack. The earthquake shaking so that the surface soil subsidence, the shallow water along the way will be squeezed by rising to the surface cracks formed to take water sandblast phenomenon. Large earthquakes can change the local terrain, or uplift or subsidence. Urban and rural areas to make split-path, distortion of the tracks, bridges broken. In the modern city, due to the breakdown of buried pipes and cables have been cut off caused by water, power and communications disrupted. Gas, radioactive materials and toxic gas leak can lead to fire and toxic, radioactive contamination, and other secondary disasters. In the mountains, landslides and earthquakes can cause landslides buried villages and towns often caused by the tragedy. The Mount rivers and landslides blocked in the upper reaches of the lake to form the earthquake. Japan in 1923 Kanto earthquake, mud-rock flow occurred in Kanagawa Prefecture, Shun down the valley, up to 5 km.
【Earthquake and the resulting type】
Earthquake Seismic divided into natural and man-made earthquake two broad categories. In addition, some special cases also have an earthquake, such as the impact of large meteorites on the ground (meteorite impact of the earthquake). Vibration caused by the Earth's surface for various reasons, according to the causes of earthquakes, earthquakes can be divided into the following categories:
1, tectonic earthquake
Due to the breakdown of rocks deep underground, the long-term dislocation accumulated energy released by a sharp, so as to the form of seismic waves spread out in all directions, to the ground shaking caused by the earthquake room structure known as the earthquake. Such an earthquake occurred most frequently, also the most destructive power, the world seismic account for about 90%.
2, vol quake
As the role of the volcano, such as magmatic activity, such as gas explosions caused by the earthquake as the volcanic earthquakes. Only in the zone of volcanic activity may have occurred before the volcanic earthquakes, an earthquake of such earthquakes around the world accounts for only about 7%.
3, the earthquake collapse
As the cave on the ground floor or at the top of the mine collapse caused by an earthquake known as the earthquake collapse. Such an earthquake the size of the relatively small number of very few, if any, tend to occur in the limestone cave clouds or large-scale mining of underground mining.
4, an earthquake-induced
Due to water storage reservoirs, oil fields, such as water triggered by seismic activity known as the earthquake-induced. Such an earthquake only in certain specific fields or reservoir areas.
5, artificial earthquake
Underground nuclear explosion, explosives and blasting ground vibration caused by man-made artificial known as the earthquake. By the man-made seismic activity caused by the earthquake. Industries such as blasting, the vibration caused by underground nuclear explosions; carried out in the deep well water, as well as large high-pressure reservoir after the water has increased the pressure on the earth's crust, sometimes induced by an earthquake.
【Earthquake expertise】
We are most familiar with the fluctuations in water is observed. When the pond to throw a stone at the water surface was upset to a rock into the water as the central Department has ripple outward expansion. The wave is out of the water in the vicinity of the water particle motion. However, the water did not spread towards the water flow in the direction; afloat if a cork surface, it will beat up and down, but not removed from the original location. The disturbance by a simple water pills before and after the campaign in a row to pass from one movement to put more particles in front of the particles. In this way, stoning to bring water to break the surface of the pool to the transport of energy shore, stirred and spray. Seismic movement and the very similar. We feel the shaking from seismic waves generated by the energy of rock elastic vibration.
The first wave just as the physical characteristics of sound waves. Sound, as well as ultrasound, are in the air by the turn of the extrusion (push) and expansion (la) and transmission. As liquid, gas and rock solid as can be compressed, the same types of wave energy in the body of water such as lakes and oceans and the solid Earth through the middle. In an earthquake, this type of wave
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