Page 199 - Science Class 08

Epicentre of an earthquake at a par cular place. Intensity

Epicentre of an earthquake is the point on the is determined from observa ons of an earth-
earth’s surface that is directly above the focus. quake’s effect on people, structure and the
Distance from epicentre to any point of interest earth’s surface.
is called epicentral distance. There are two major scales in which earth-

Magnitude quakes are measured. These two scales are—
the Mercalli Scale and the Richter Scale.
Earthquake magnitude is the measure of the
strength of an earthquake or the strain energy Richter Scale
released by it. It is calculated from the On a Richter Scale, only units from 1 to 10 are
instrument record made by the event on a used. But, unlike many other scales in Science,
calibrated seismic-graph. Richter Scale is not linear. This means, each one
unit on this increase in the earthquake strength.
Therefore, an increase of 2 in magnitude means

1000 mes more destruc ve energy.
SEISMIC ZONES IN INDIA
You have studied that earthquakes are caused
by the movement of plates, the boundaries

of the plates are the weak zones where earth-
quakes are more likely to occur. The
weak zones are also known as seismic or fault
Seismograph zones.
Seismograph is simply a vibra ng rod or a ZONE 1
pendulum which begins to vibrate as soon as ZONE 2
ZONE 3
ZONE 4
tremors occurs. A pen is a ached to the ZONE 5
vibra ng system. The pen records the seismic CHINA
waves on a paper which moves under it. The PAKISTAN TIBET

scien sts analyse these waves to construct a NEPAL
BHUTAN
complete map of the earthquake. They can also
es mate its power to cause destruc on. Tropic of Caner
MYANMAR
Frame BANGLADESH
Wire
Weight ARABIAN BAY
OF
SEA BENGAL
Rota ng Drum
Vibra ons
ZONE 1 Intensity 5 or below
(moderate)
ZONE 2 Intensity 6 (strong)
ZONE 3 Intensity 7 (very strong)
ZONE 4 Intensity 8 (destructive)
Base (INDIA) LAKSHADWEEP ZONE 5 Intensity 9 and above
(very disastrous)
Seismograph
SRI
LANKA
Intensity
I N D I A O C E A N
Earthquake intensity is a measure of the effects Earthquake Prone Areas

Science-8 199