Page 109 - SST Class 07
P. 109
Charles Richter. An earthquake measuring 2.0 or
Activity less intensity is hardly noticeable; however, with
Make a list of volcanoes and divide them into : the increase in points, an earthquake assumes
destructive proportions. An increase in a point
(a) active volcanoes (b) dormant volcanoes
shows a magnitude ten times more intense; for
(c) extinct volcanoes example, an earthquake measuring 5.0 can cause
some damage, but the one measuring 6.0 is ten
Quiz Time times more intense and can cause a lot of damage.
An earthquake measuring 7.0 or more is very
Fill in the blanks :
destructive.
1. The earth movements can be ___________ or
___________ .
2. The magma may accompany with particles of
___________ , ___________ and ___________ .
3. The forces which work within the earth are
called ___________ .
4. Volcanoes erupt rarely are called ___________ .
EARTHQUAKES Destruction caused by an earthquake
Earthquakes are sudden movements which are Info Bits
Info Bits
caused by the movement of tectonic plates and
eruption of volcanoes. The earthquakes resulting One of the best way to avoid destruction in an
from volcanoes are limited along the Ring of Fire. earthquake is to build buildings which can bear
with the impact of an earthquake. Beams and
The earth’s crust is made up of 15 major and
several minor plates, called tectonic plates. The pillars should be used in the whole building so that
magma inside the earth causes movement of these the damage can be minimised.
plates. These plates move very slowly, only a few An earthquake under the sea surface can result in
millimetres in a year, in relation to one another. high waves of seawater which can cause a lot of
This movement is called tectonic movement . damage to the places near the seashores. Such sea
When these plates move, vibrations are caused. waves are called tsunami. In 2005, an earthquake
These vibrations are called earthquakes. in South-East Asia caused a mammoth tsunami,
Earthquakes occur where the earth’s crust is weak. resulting in widespread damage in many
countries, including India.
The place where the vibrations originate within
the earth’s interior is called the focus . From this It is not yet possible to predict the occurrence of
point, the vibrations or seismic waves travel in all an earthquake. It is believed that strange animal
directions. The place right above the focus is behaviour can be used for this purpose, but this is
called the epicentre . This is the place which is uncertain because it can occur due to some other
impacted the most and suffers maximum damage. aspects also. Such animal behaviour comprises of
The strength of vibrations decreases away from the abnormal behaviour on the part of fish, animals
epicentre. and birds.
An earthquake is measured F ind Outind Out
with a seismograph . The
magnitude of an earthquake
What kind of houses should we build in
is measured on the Richter earthquake-prone areas to avoid major loss of lives
Scale . It was invented by and properties?
A Richter scale
Changing Earth and Landforms
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