Earthquake for Competitive Exam
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A fault is a sharp break in the crustal rocks.
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All natural earthquakes occur in the lithosphere.
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An earthquake is, simply put, shaking of the earth’s
crust.
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It is caused due to the energy release, which triggers
waves that travel in all directions.
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Rocks along a fault generally move in opposing
directions.
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Seismic wave studies offer a full picture of the layered
interior.
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The emanation of energy occurs along a fault.
Types of Earthquakes
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Collapse earthquake: This earthquake occurs in underground mines. The
main cause is pressure generated within the rocks.
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Explosion earthquakes: The occurrence of this type of earthquake is
artificial. High-density explosion such as nuclear explosions is the primary
cause.
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Tectonic earthquakes: The most common form of earthquakes, is caused by
the movement of loose fragmented pieces of land on earth’s crust knowns as
tectonic plates.
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Volcanic earthquake: The less prevalent compared to the tectonic
variety, these earthquakes happen before or after the eruption of
a volcano. It is caused when magma leaving the volcano is filled by rocks
being pushed to the surface.
Causes of Earthquakes
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It is caused due to
the tectonic movements of the earth.
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The energy release
produces waves that travel in all directions.
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The point where
energy is released is called the focus or hypocentre. It is generally
located at a depth of 60 km.
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This causes a release
of energy, and the energy waves travel in all directions.
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The point where the
energy is released is called the focus of an earthquake or hypocenter.
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The point on the
surface of the earth which is vertically above the focus is called the
epicentre. It is the first place to experience the waves.
Body Waves
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Earthquake waves are
of two types — body waves and surface waves.
P- Waves
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P-waves are also
known as the Primary waves. They are the first waves to arrive at the surface.
The characteristics of P-waves are like sound waves. They travel through all
three mediums- solid, liquid, and gas. These waves tend to vibrate parallel to
the direction of wave propagation. This causes density differences in the
material through which they travel. These waves are responsible for elongating
and squeezing of material.
S- Waves
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S- Waves arrive after
some time after the happening of Earthquake and they are called secondary
waves. A significant characteristic of these S-waves is that they travel only
through a solid medium. The direction of vibration of this S-wave is
perpendicular to the direction of wave propagation, thereby creating crests and
troughs in the material of their transmission.