Transcript What are earthquakes?

Learning Objectives
To understand:
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•
what earthquakes are
what causes them
where they are located
ways of recording and measuring
earthquakes
• the effects of earthquakes
What are earthquakes?
Earthquakes are ‘a sudden and violent
movement, or fracture, within the
earth followed by the series of
shocks resulting from this fracture’.
(The Concise Oxford Dictionary of Geography, 1992)
What causes Earthquakes?
Earthquakes happen mainly along the
boundaries of the Earth’s plates.
At plate boundaries two separate parts of the
Earth’s crust either move towards, or past
each other.
As plates rub against each other friction can
lock them together.
What causes Earthquakes?
Over time pressure builds up until
eventually it becomes so great the rock
slips suddenly along a weak area called a
fault line.
The focus is the place underground where
the rock actually slips.
The place at the surface directly above
the focus is called the epicentre.
What causes Earthquakes?
As the built up energy is released it travels
outwards as shockwaves which are known
as
These seismic waves cause the Earth
crust to shake and tremor which can
cause a lot of damage on the earth
surface.
As the seismic waves move through the
crust they lose energy so less damage is
caused further away from the epicentre.
Task
Who wants to have a go at labelling where:
a) focus
b) fault line
c) epicentre
d) seismic waves
are on the diagram on the white board?
Now complete the diagram for the handout
you have been given….
Seismic waves
Epicentre
Earthquake Focus
Fault line
Can you name the plate boundaries?
DESTRUCTIVE
CONSERVATIVE
Earthquakes can occur at
the 4 main plate
boundaries but the most
powerful earthquakes are
normally at DESTRUCTIVE
and CONSERVATIVE
boundaries.
Location of Earthquakes
Earthquakes are mainly found in long
narrow belts across the earths surface
following the plate boundaries.
Due to the friction at plate
boundaries these are also
areas where volcanoes are
often located.
The map on the next slide illustrates the
location of earthquake activity…..
Task
On the map on your handout draw and name
the major earthquakes in the world.
Use page 27 of Interactions textbook to
help you.
Recording and measuring Earthquakes
Seismic waves (shockwaves) from
earthquakes are recorded by
scientists on seismometers.
Seismic waves from the other
side of the world can be picked up
(detected) by seismometers.
A simplified
drawing of a
seismometer.
Earthquake strength can be measured
using 2 different scales – the Mercalli
scale and the Richter scale.
The Mercalli Scale
The Mercalli scale measures the amount of
damage done by the earthquake in a certain
area.
The Mercalli scale ranges from 1 to 12
(1=least damage, 12 =most damage).
Look at your handout can you put the
pictures on the following slide in order?
(some have been done for you)
Can you put these pictures in order?
Let’s see if you got it right...
1
5
2
6
10
3
7
11
4
8
12
9
Richter Scale
Richter Scale
Possible effects
Richter scale is used to
measure the scale (magnitude)
of earthquakes from 0 to 10,
of the amount of energy
released.
Only detected by instruments
Faint tremor, little damage
Distinct shaking
Major earthquake
It is a logarithmic scale which
means that a size ‘7’ on the
scale is 10 times larger than a
size ‘6’. A size ‘7’ is 100 times
larger than a size ‘5’ (10 x 10 =
100).
Widespread destruction
The largest earthquake
ever recorded was in
Chile (1960). It measured
8.9 on the Richter Scale.
Lets see by clicking the
information button how much
the screen would shake during
an earthquake depending on its
size, using the Richter Scale.
The effects of earthquakes
Primary effects are the immediate effects
caused directly by the earthquake. These
include:
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Damage or collapse buildings
Damage to other infrastructure (e.g. roads,
bridges, railway lines)
Falling objects (signs or glass from
buildings)
Injury or death to Human Life
The effects of earthquakes
Secondary effects are indirect effects
and problems faced after an earthquake.
These include:
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Fires (caused by burst gas pipes)
Lack of food and water
Spread of disease (cholera and typhoid)
Tsunami (huge waves of up to 30 metres
high and travelling up to 500km hour)
Task
Discuss with a partner the following
photographs taken after an earthquake and
decide what effects they are trying to
show.
Then decide whether this effect is
primary or secondary.
1. Fire
2. Collapse buildings
3. Collapse bridge
4. Damaged railway line
5. Tsunami
7. Communication lines stopped
6. Falling objects
8. Spread of disease
Copy and complete the table
Effect shown
1. Fire
2. Collapse buildings
3. Collapse bridge
4. Damaged railway
line
5. Tsunami
6. Falling objects
7. Communication lines
stopped
8. Disease
Primary
Secondary