بحث بالانجليزية عن الكوارث الطبيعية Natural disasters

An earthquake (also known as a quake, tremor or temblor) is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity or seismic activity
of an area refers to the frequency, type and size of earthquakes
experienced over a period of time. Earthquakes are measured with a seismometer (also called a seismograph). The moment magnitude (or the obsolete Richter
magnitude, numerically similar over the range of validity of the
Richter scale) of an earthquake is conventionally reported, with
magnitude 3 or lower earthquakes being mostly almost imperceptible and
magnitude 7 and over causing serious damage over large areas. The
largest earthquakes in historic times have been of magnitude slightly
over 9, although there is no limit to the possible magnitude. The most
recent large earthquake of magnitude 9.0 or larger was a 9.0 magnitude earthquake in Japan in 2011
(as of March 2011), and it was the largest Japanese earthquake since
records began. Intensity of shaking is measured on the modified Mercalli scale. The shallower an earthquake, the more damage to structures it causes, all else being equal.[1]
At the Earth's surface, earthquakes manifest themselves by shaking and
sometimes displacement of the ground. When a large earthquake epicenter is located offshore, the seabed may be displaced sufficiently to cause a tsunami. Earthquakes can also trigger landslides, and occasionally volcanic activity.
In its most general sense, the word earthquake
is used to describe 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 such as volcanic activity, landslides, mine blasts, and nuclear tests. An earthquake's point of initial rupture is called its focus or hypocenter. The epicenter is the point at ground level directly above the hypocenter

Naturally occurring earthquakes

Tectonic earthquakes occur anywhere in the earth where there is
sufficient stored elastic strain energy to drive fracture propagation
along a fault plane. In the case of transform or convergent type plate boundaries, which form the largest fault surfaces on earth, they move past each other smoothly and aseismically only if there are no irregularities or asperities
along the boundary that increase the frictional resistance. Most
boundaries do have such asperities and this leads to a form of stick-slip behaviour.
Once the boundary has locked, continued relative motion between the
plates leads to increasing stress and therefore, stored strain energy in
the volume around the fault surface. This continues until the stress
has risen sufficiently to break through the asperity, suddenly allowing
sliding over the locked portion of the fault, releasing the stored energy. This energy is released as a combination 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
referred to as 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 used to power the earthquake fracture growth or is converted into heat generated by friction. Therefore, earthquakes lower the Earth's available elastic potential energy
and raise its temperature, though these changes are negligible
compared to the conductive and convective flow of heat out from the
Earth's deep interior.[2

The definition of natural disasters
Natural disasters are a test or significant damage caused by a natural event inclosed risk, such as volcanic eruptions, earthquakes, hurricanes and other natural phenomena that cause significant damage to property and human beings, in thethe event of a natural phenomena in uninhabited areas are not called ( natural disasters) . Different disasters by the proportion of people surrounding a natural phenomenon of folding or are at risk, many of the communities living near the volcano with a history of devastating, as happened in Pompeii, etc. This is due to human nature and the problems of poverty and others

The most important factors that cause natural disasters
First: Earthquakes
Ahtazar earthquake is ground sequentially as a result of fast break rocks and tectonic movement of the rocks, leading to vibration Aloradw as a result of geological effects caused by the movement of plate tectonics. Is called the earthquake. May arise as a result of earthquake or volcanic activities as a result of the presence of landslides in the layers of the Earth (plate tectonics).
Lead earthquakes (the negatives) to the cracking of the ground and break, of a high waves (positive side) depletion of springs or the appearance of springs new if what you got under the surface of the sea as well as its sabotage of buildings and transportation, facilities, buildings, etc. often result in movements of convection in the layer Alostinosver which Movement of continental plates, causing the occurrence of an earthquake tremors.
The emergence of earthquakes:
May arise as a result of earthquake or volcanic activities as a result of the presence of landslides in the layers of the earth. Cause earthquakes to rupture of the earth and the depletion of springs or the appearance of springs of new or the occurrence of high waves if they get below the surface of the sea (the tsunami) as well as its destructive to buildings, transportation and facilities and often result in movements of convection in Alostinosver that drive continental plates, causing the occurrence of earthquakes are earthquakes.
.

II: Drought
Drought is that the weather changes in terms of temperature and precipitation, ie, causes lead to dehydration and may lead to famine, especially in a country that depends on agriculture. One of the greatest threats that affect the land, such as famine in southern Africa (due to drought)

Third: Hurricanes
Are the storms of air rotary screw violent, usually arise over tropical seas, and therefore known as typhoons or tropical or cyclones because the cold air (a high pressure) where there is around the center of inhabitants of warm air (a low-pressure), and then rush this storm in The direction of land deprives the velocities of friction with the Earth's surface, but still moving at speeds of up to more than 300 kilometers per hour. The diameter of the vortex per 500 kilometers, and may continue for several days to two weeks in a row. And accompanied by that all the clouds Layering and cumulus to the high of 15 kilometers and is moving hurricane in straight lines or curved which makes her enormous devastation on the land because of the speed of the big flash, and accompany heavy rain and flooding, in addition to the phenomena of lightning and thunder, as it may cause a hurricane in the high waves of the sea and destroys Villages and cities

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