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Earthquake - A Natural Disaster short brief, causes and preventive measure

Earthquake - A Natural Disaster short brief, causes and preventive measure
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Earthquake is shaking of the earth's surface due to the sudden release of energy within the Earth's lithosphere which creates seismic waves. Earthquakes can home in size from folks that are so weak that they will not be felt to those violent enough to propel objects (and people) into the air, and wreak destruction across entire cities. The seismicity, or seismic activity, of a neighborhood, is that the frequency, type, and size of earthquakes experienced over a period of your time. The word tremor is additionally used for non-earthquake seismic rumbling.

Source: Wikipedia 

Earthquake, any sudden shaking of the bottom caused by the passage of seismic waves through Earth’s rocks. Seismic waves are produced when some quite energy stored in Earth’s crust is suddenly released, usually when masses of rock straining against each other suddenly fracture and “slip.” Earthquakes occur most frequently along geologic faults, narrow zones where rock masses move in reference to each other. The major fault lines of the planet are located at the fringes of the large tectonic plates that structure Earth’s crust. (See the table of major earthquakes.)
At the surface, earthquakes manifest themselves by shaking and displacing or disrupting the bottom. When the epicenter of an outsized earthquake is found offshore, the seabed could also be displaced sufficiently to cause a tsunami. Earthquakes also can trigger landslides and infrequently, volcanic activity.

In its most general sense, the word earthquake is employed to explain any seismic event—whether natural or caused by humans—that generates seismic waves. Earthquakes are caused mostly by rupture of geological faults but also by other events like volcanic activity, landslides, mine blasts, and nuclear tests. An earthquake's point of initial rupture is named its focus or hypocenter. The epicenter is that the point at ground level directly above the hypocenter.

Naturally occurring earthquakes

Three types of faults:

A. Strike-slip
B. Normal
C. Reverse
Tectonic earthquakes occur anywhere within the planet where there's sufficient stored elastic strain energy to drive fracture propagation along a fault plane. The sides of a fault move past one another smoothly and aseismically as long as there are not any irregularities or asperities along the fault surface that increase the frictional resistance. Most fault surfaces do have such asperities, which results in a sort of stick-slip behavior. Once the fault has locked, continued relative motion between the plates leads to increased stress and thus, stored strain energy within the quantity round the fault surface. This continues until the strain has risen sufficiently to interrupt through the asperity, suddenly allowing sliding over the locked portion of the fault, releasing the stored energy. This energy is released as a mixture of radiated elastic strain seismic waves, frictional heating of the fault surface, and cracking of the rock, thus causing an earthquake. This process of gradual build-up of strain and stress punctuated by occasional sudden earthquake failure is mentioned because of the elastic-rebound theory. It is estimated that only 10 percent or less of an earthquake's total energy is radiated as seismic energy. Most of the earthquake's energy is employed to power the earthquake fracture growth or is converted into heat generated by friction. Therefore, earthquakes lower the Earth's available elastic P.E. and lift its temperature, though these changes are negligible compared to the conductive and convective flow of warmth out from the Earth's deep interior.

Measures against earthquakes

Personal measures

  1. Seek shelter under stable tables or under door frames.
  2. If outside, stand back from buildings, bridges and electricity pylons and move to open areas.
  3. Avoid areas in danger from secondary processes, like landslides, rockfall and soil liquefaction.
  4. After an earthquake, check gas, water and electricity pipes and features for damage.
  5. Listen to the radio and follow the instructions issued by the authorities.

Technical/biological measures

  1. No measures are often taken to stop earthquakes themselves, however, limited measures exist which may counteract their secondary effects like landslides, rockfall and soil liquefaction.
  2. Earthquake-proof planning and design of buildings
  3. The micro zoning of the local geological substratum provides indicators of areas during which tremors will have a very strong or attenuated effect.

Causes of earthquakes

Earth’s major earthquakes occur mainly in belts coinciding with the margins of tectonic plates. This has long been apparent from early catalogs of felt earthquakes and is even more readily discernible in modern seismicity maps, which show instrumentally determined epicenters. The most important earthquake belt is that the Circum-Pacific Belt, which affects many populated coastal regions around the Pacific Ocean—for example, those of New Zealand, New Guinea, Japan, the Aleutian Islands, Alaska, and therefore the western coasts of North and South America. It is estimated that 80 percent of the energy presently released in earthquakes comes from those whose epicenters are during this belt. The seismic activity is by no means uniform throughout the belt, and there are a variety of branches at various points. Because at many places the Circum-Pacific Belt is related to volcanic activity, it's been popularly dubbed the “Pacific Ring of fireside .”

A second belt, referred to as the Alpide Belt, passes through the Mediterranean region eastward through Asia and joins the Circum-Pacific Belt within the Malay Archipelago. The energy released in earthquakes from this belt is about 15 percent of the planet's total. There are also striking connected belts of seismic activity, mainly along oceanic ridges—including those within the Arctic Ocean, the Atlantic, and therefore the western Indian Ocean—and along the rift valleys of East Africa. This global seismicity distribution is best understood in terms of its plate tectonic setting.
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