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SAI INTERNATIONAL SCHOOL
STD VII SUBJECT - GEOGRAPHY
TOPIC-CH – 3- Our Changing Earth(LESSON NOTES)

Sub-topic- Earthquake, case study

ÿ NOTES- Earthquake- a sudden violent shaking of the ground, typically causing
great destruction, as a result of movements within the earth's crust or volcanic
action.

ÿ An earthquake is what happens when two blocks of the earth suddenly slip past
one another.

ÿ The focus of an earthquake is the point where the rocks start to fracture. It is the
origin of the earthquake. The epicenter is the point on land directly above the
focus.

ÿ Epicenter- the point on the earth's surface vertically above the focus of an
earthquake.

ÿ Seismic waves -are waves of energy that travel through the Earth's layers, and
are a result of earthquakes, volcanic eruptions, magma movement,
ÿ Types of seismic waves-
ÿ P-waves- primary waves ,they are fastest
ÿ S-waves- secondary waves, they are slower
ÿ L-waves-are surface waves

ÿ Earthquakes are measured using seismographs, which monitor the seismic
waves that travel through the Earth.
ÿ The Richter magnitude scale is a scale of numbers used to tell the power (or
magnitude) of earthquakes.
ÿ It is very difficult to predict an earthquake however animals, fish, birds,
reptiles, and insects exhibits strange behavior anywhere from weeks to seconds
before an earthquake.
ÿ 2001 Gujarat earthquake, also known as the Bhuj earthquake, occurred on 26
January, India's 52nd Republic Day, at 08:46 am IST.
ÿ The earthquake's epicentre was 20km from Bhuj.

ÿ Magnitude: 7.9 on the Richter Scale, Compression Stress between region’s
faults, Indian Plate Sub ducting beneath Eurasian Plate
ÿ The earthquake devastated Kutch. Practically all buildings and structures of
Kutch were brought down.
ÿ Ahmedabad, Rajkot, Jamnagar, Surendaranagar and Patan were heavily
damaged.