Page 198 - Science Class 08
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There are many natural phenomena which can very low magnitude. Major earthquakes do not
be predicted well before their occurring. These occur frequently. They can cause immense
natural phenomena are thunderstorms, cycl- damage to buildings, bridges, dams and people.
ones, floods, etc. The weather department can There can be great loss of life and property.
warn about a thunderstorm or cyclone
developing an area. So, people can move to
safer places well before me. But, there is one
natural phenomenon which we are not yet able
to predict accurately. It is an earthquake.
It has a great devasta ng capacity which can
kill thousands of people in a few minutes and
can damage the property worth millions of
rupees at a me.
An Earthquake
Earthquakes can also cause floods, landslides
and tsunamis. When an earthquake of high
On October 8, 2005 a devasta ng earth-
quake rocked Pakistan, Afghanistan and intensity at the sea bed occurs it can trigger
India. The epicenter of the earthquake was tsunami. A major tsunami occurred in the
at Muzaffarabad in Pakistan Occupied Indian Ocean on 26 December, 2004. It caused
Kashmir (POK) and its intensity was a great destruc on to coastal areas around
measured 7.4 on the Richter Scale. the ocean.
Mujaffarabad, Islamabad and adjoining areas CAUSES OF EARTHQUAKES
were worst affected. It is es mated that over The crust of the earth is composed of several
70,000 people lost their lives and more than big and small por ons called plates. These
86,000 people got seriously injured. Besides,
plates are on con nuous movement on the
lakhs of people became homeless alone in molten and semi-molten state. This is called the
Pakistan due to this earthquake.
tectonic movement.
The impact of this earthquake was also
Most earthquakes result from the movement of
experienced in some North – Western states
of India. However, the destruc on in India one rock mass to another in response to
was not at large. tectonic forces. When the stress exceeds the
strength of the rock, the rock breaks along a
What is an Earthquake? preexis ng or new fracture plane called fault.
An earthquake is a sudden movement or This results in vibra ons in all direc ons. The
displacement of the ground produced by abrupt vibra ons move in all direc on called seismic
displacement of rock masses, usually within the waves.
upper 15 to 20 km of the earth’s crust. EARTHQUAKE TERMINOLOGY
Earthquakes occur all the me, all over the Focus
earth. But, we generally do not no ce all of It is the point within the earth from where
them. It is because, most of them are of low or seismic waves originate.
198 Science-8
