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Earthquakes

The general concept
Briefly

The earthquake - tremors and vibrations of the earth's surface due to natural causes (mainly by tectonic processes), or artificial processes (explosions, the filling of reservoirs, underground cavities collapse of mine workings). Small bumps can also be caused by the rise of the lava during volcanic eruptions .. 

Every year on Earth is about one million earthquakes, but most of them are so small that they go unnoticed. Indeed the strong earthquake that can cause extensive destruction of the planet occur about once every two weeks. Most of them have at the bottom of the ocean, and therefore is not accompanied by disastrous consequences (if an earthquake under the ocean do without the tsunami). 

Earthquakes are most known for the devastation to which they are able to produce.The destruction of buildings and structures caused by fluctuations in soil or giant tidal waves (tsunamis) that arise when seismic shifts on the seabed. The international network of observations records for the earthquakes, even the most remote and little of them. 


In detail 

The earthquake - rapid offset fluctuations in the Earth's surface as a result of aftershocks. Small earthquakes can be caused by strong explosions, collapsing arches voids underground cavities - mining, natural cavities (karst caves). Small bumps can cause the rise of the lava during volcanic eruptions. 

But most of the earthquake (a bolshiezemletryaseniya always) caused by rapid displacement of the crustal section as a whole at the time of the plastic (brittle) deformation of the elastically strained rocks in the earthquake. Most of the earthquake occurs near the surface of the Earth. Of course the shift occurs under the action of elastic forces due to the discharge, reduction in the amount of elastic deformation of plates in the area during his shift on to the other words, the earthquake is the rapid transition of the potential energy stored in the elastically deformed (compressed, stretched or Sliding) rocks subsurface in the vibrational energy of the very depths of (seismic waves), the energy changes in the structure of rocks in the earthquake. This transition occurs at the time of exceeding the tensile strength of rocks in the earthquake.
 
Tensile strength of crustal rocks is exceeded as a result of the sum of forces acting on it: 

1.Sily viscous friction of mantle convection currents of the earth's crust; 
2.Arhimedovoy forces acting on a light crust on the part of a heavier plastic mantle; 
3.Lunno-solar tides; 
4.Izmenyayuschegosya atmospheric pressure.
These same forces also lead to an increase in the potential energy of elastic deformation of rock resulting from the displacement of plates under their influence.
The density of the potential energy of elastic deformation under the action of these forces is growing in almost the entire volume of plates (in different ways at different points). At the time of the earthquake potential energy of elastic strain in the outbreak zemletryaseniyabystro (almost instantly) is reduced to the minimum residual (almost to zero). While in the vicinity of the source due to the shift in the earthquake as a whole slab elastic strains increase somewhat. 

Therefore, occur frequently in the vicinity of the main recurrent earthquakes - aftershocks. Similarly, the small "preliminary" earthquake - foreshocks - can provoke a lot in the vicinity of the initial small earthquake. A large earthquake (with a large shear plates) can cause subsequent индуцированныеземлетрясения even at the edges of the plates removed. Of these forces the first two a lot more 3rd and 4th, but their rate of change is much less than the rate of change of tidal and atmospheric forces.Therefore, the exact time of arrival of the earthquake (year, day, minute) is determined by changes in atmospheric pressure and tidal forces. Then how much more, but slowly varying viscous forces and buoyancy forces set the arrival time of the earthquake (with the focus at this point) up to centuries and millennia. 

Every year on Earth is about one million earthquakes, but most of them are so small that they go unnoticed. Indeed the strong earthquake that can cause extensive destruction of the planet occur about once every two weeks. Fortunately, most of it falls on the bottom of the ocean, and therefore is not accompanied by disastrous consequences (if an earthquake under the ocean do without the tsunami). 

Deep-focus earthquake foci are located at depths of up to 700 km from the surface, occur at convergent boundaries of lithospheric plates and are associated with subduction. Earthquakes are most known for the devastation to which they are able to produce. The devastation caused by fluctuations in soil or giant tidal waves (tsunamis) that arise when seismic shifts on the seabed. 

Intensity is a qualitative characteristic of an earthquake, and indicates the nature and extent of the impact of earthquakes on the surface of the earth, people, animals and the natural and man-made structures in the earthquake area. 

In a world of multiple scales of intensity: 
• In the United States - Modified Mercalli Scale (MM); 
• Europe - The European macroseismic scale (EMS); 
• Japan - the scale of Shindo (Shindo). 
 The scale of the Medvedev-Karnik-Shponhoyera (GMT-64) 
12-point scale Medvedev-Karnik-Shponhoyera was developed in 1964 and is widely used in Europe and the USSR. Since 1996, the European Union adopts a more modern European macroseismic scale (EMS). 
MSC-64 is at the heart SniP-11-7-81 "Construction in seismic regions", and is still used in Russia and CIS countries. 

Earthquake begins to rupture and displacement of rock in some place in the tsentreZemli. This place is a hotbed of earthquake or hypocenter. Its depth is usually not more than 100 miles, but sometimes reaches up to 700 km. Sometimes, the earthquake may be the Earth's surface. In such cases, eslizemletryasenie strong, bridges, roads, houses and other buildings are destroyed, and dissociation. 

A plot of land, within which on the surface, over the fire, the force of earthquakes is highest, is called the epicenter. In some cases, layers of earth on the sides of the fault, approaching each other. The other - the land on one side of the fault falls, forming discharges. In places where they cross the river beds, there are waterfalls.The vaults are underground caves crack and break down. It happens that after the earthquake, large tracts of land and sink filled with water. 

Earthquakes are shifting from the slopes of the upper, unconsolidated soil layers, forming landslides and mudslides. During an earthquake in California in 1906 formed a deep crack on the surface. It stretches for 450 kilometers. It is clear that a sharp movement of large masses of land in the hearth must be accompanied by a tremendous blow to the forces. 

For the year people can feel about 10 000 earthquakes. Of these about 100 are devastating.

 

Автор: admin от 03.03.2012





  

 

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