Earthquakes
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© Boardworks Ltd 2003
What are earthquakes and where do they occur?
DESTRUCTIVE
CONSERVATIVE
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Earthquakes are
vibrations caused by
earth movements at plate
boundaries and at major
fault lines (cracks in the
earth’s surface).
They can occur at all 4
major plate boundaries
but the most severe
earthquakes are normally
found at CONSERVATIVE
and DESTRUCTIVE
boundaries.
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Why do earthquakes happen?
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How can we measure earthquakes?
The Richter Scale
This measures the magnitude of a
tremor (how powerful it is) using an
instrument called a seismograph.
On the Richter Scale, magnitude is
expressed in whole numbers and
decimal fractions. Although the
Richter Scale has no upper limit, the
largest known shocks have had
magnitudes in the 8.8 to 8.9 range. It
is a logarithmic scale which means
that a size ‘6’ on the Richter Scale is
10 times larger than a size ’5’ and
100 times larger than a size ‘4’.
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1
2
3
4
5
6
7
8
9
10
Richter
Scale
The largest earthquake
ever recorded was in
Chile. It measured 8.9
on the Richter Scale.
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How can we measure earthquakes?
The Japanese earthquake in Kobe
(September 1995) measured 7.2 on the
Richter Scale.
The Greek earthquake (June 1995)
measured 6.2 on the Richter Scale.
1
2
3
4
5
6
7
8
9
10
Richter
Scale
How many times greater was the Japanese earthquake?
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A seismograph
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Mercalli Scale
Mercalli Scale
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This measures
how much
damage is
caused by the
earthquake
based on
observations. It
is measured on a
scale between I
and XII.
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Activity
Design your own cartoon based on the Mercalli Scale
descriptions below.
I
II
III
IV
V
VI
VII
VII
IX
X
XI
XII
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Felt by almost no one.
Felt by very few people.
Tremor noticed by many, but they often do not realise it is an
earthquake.
Felt indoors by many. Feels like a truck has struck the building.
Felt by everyone; many people are awakened. Swaying trees and
poles may be observed.
Felt by all; many people run outdoors. Furniture is moved.
Everyone runs outdoors. Poorly built structures considerably
damaged. Slight damage elsewhere.
Specially designed structures damaged slightly, others collapsed.
All buildings considerably damaged, many shift off foundations.
Noticeable cracks in the ground.
Many structures destroyed. Ground badly cracked.
Almost all structures fall. Bridges wrecked.
Total destruction. Waves seen on ground surfaces, objects are
tumbled and tossed.
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Epicentre and focus
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Epicentre and focus
Focus
Epicentre
An earthquake has occurred along this fault line.
Match the letter with the correct label.
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Epicentre and focus
An earthquake has occurred in this area.
Which area (the town or the forest) will receive the stronger
earthquake?
Which area will receive more damage from the earthquake?
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How can we limit earthquake damage?
predict
plan
protect
water levels can rise in
wells and lakes because
of cracks in the rock
a tiltmeter can check any
movement within the rocks
1. predict
foreshocks before the main
quake can be detected by a
seismometer
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animals can act
strangely before the
earthquake
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How can we limit earthquake damage?
advise people to plan for an
earthquake (eg tell them to
turn off the gas, find a ‘safe’
place in their homes, pack
an emergency kit)
make an emergency plan
2. plan
enforce regulations to
make some buildings
earthquake proof
organize regular
‘earthquake practices’
for offices and schools
What should people pack in their emergency kit?
Design a poster reminding people what to do in an earthquake.
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This is San Francisco in the USA.
Why does this skyscraper have a wide base?
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Building regulations in earthquake zones
overlapping bricks
strong lintels
deep foundations
What other measures would make buildings less likely to
collapse in an earthquake?
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Which shape of building would be most ‘earthquake proof’?
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Sky’s the limit!
This is the Sky Tower in Auckland, New Zealand.
Sky Tower is the tallest tower in the Southern
Hemisphere and the twelfth tallest in the World.
Sky Tower is 328 metres tall (more than 1,076
feet); that's about 37 buses standing end on
end!
Sky Tower weighs 21 million kilos (20,000
tonnes) which is equivalent to 6,000 elephants.
Problem – Auckland is in an earthquake zone.
How could you make buildings such as the Sky Tower
more ‘earthquake proof’?
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What they did…
Sky Tower is constructed from a high strength, high
performance concrete.
The main structure of Sky Tower is a reinforced concrete
shaft measuring 12 metres in diameter. It is supported by
eight reinforced concrete 'legs' at the base, connected to
the shaft by a concrete collar and designed to spread force
load.
Sky Tower's foundations go down more than 15 metres.
The tower was tested to see if it would withstand
earthquakes. Analysis shows that an earthquake
measuring 7.0 on the Richter scale, located 40 kilometres
from Sky Tower on the Kerepehi Fault, would leave Sky
Tower essentially undamaged. In the extreme event of a
magnitude 8.0 earthquake occurring within 20 kilometres of
the tower, analysis shows that Sky Tower would remain
standing.
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Turkish earthquake (August 1999)
The magnitude of the earthquake was higher
than first thought, measuring 7.4 on the Richter
Scale. Seismologists expect a large number of
aftershocks, possibly for up to a year. These
could bring down the damaged buildings.
The search continues for survivors, but
temperatures, 30ºC in the day and 10ºC at
night, are far from ideal. International rescue
Fact File
teams carry on searching for up to 72 hours
(3 days after the
after a disaster, but it has been known for
earthquake)
people to survive much longer than this. The
longest survival is 17 days by a Korean who
Dead : 10,059
chewed cardboard and drank his own urine
Missing : up to 35,000
Injured : over 45,000
before being rescued.
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Turkish earthquake (August 1999)
You are in charge of the earthquake task force in Turkey.
It is three days after the earthquake.
Put these problems in the order of urgency. Explain your
choice.
Organize emergency camps and supplies for the survivors
Bury the dead
Stabilize the damaged buildings
Organize emergency hospital to look after injured
Search for more survivors
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If the epicentre of an earthquake is at ‘A’, which settlement
will be damaged the most? Give reasons for your answer.
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Factors affecting the damage caused by earthquakes
size of the earthquake
emergency services
building design and construction
time of day
education
physical landscape
1) Which factor/s do you think are the most important?
2) Which factors are related to the wealth of the country?
3) How can the education of the population affect the
amount of damage caused by an earthquake?
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Read the following two slides.
Compare the earthquake in Los Angeles (94) with the
earthquake in Turkey (99) using the following table (you will
need an atlas to help with your research).
Why were there more deaths in the Turkish earthquake?
number of deaths
Los Angeles
Turkey
size of the earthquake
time of day
emergency services
building design and construction
education
GNP (wealth)
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Los Angeles earthquake (1/94)
Earthquake struck on holiday honouring Dr Martin
Luther King….57 dead
Fires burned out of control last night after a devastating earthquake
measuring 6.6 on the Richter Scale hit LA. Over fifty people have
been killed including fourteen people trapped in a collapsed bock
of flats, near the epicentre, in the district of Northridge. Reports
suggest that over one thousand people are injured and
the city is at a standstill. Freeways have buckled, trains have been
derailed and the airport is closed. The earthquake struck before
dawn and was felt over a wide area. The quake was felt as far
away as Las Vegas, 125 miles away to the east!
Emergency shelters have been set up by the Salvation Army and
the Red Cross. In addition, twelve search and rescue teams and
four medical teams have been sent to the quake zone. The teams
are using dogs, sensitive listening devices and tunnelling
equipment to look for survivors.
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Turkey earthquake (8/99)
Izmit buildings substandard
The earthquake that hit Turkey last month has resulted in an estimated death
toll of between 30,000 and 40,000. The earthquake that measured 7.4 on the
Richter Scale, struck at 3am. It had an epicentre approximately 11 km to the
south east of Izmit and it was felt as far as 320km away.
Turkey received international help to rescue the thousands trapped in collapsed
buildings. At least 20,000 buildings collapsed or suffered heavy damage. The
buildings which collapsed were mainly between 6 and 8 stories high and had
been built in the last few years. Although new buildings in earthquake areas are
supposed to follow the ‘Uniform Buildings Code’ (California), many of these
buildings were poorly constructed in concrete and had unreinforced masonry
walls.
Concerns were also raised over the fact that the Tupras oil refinery in Korfez
was allowed to be built so close to the North Anatolian Fault. The oil refinery
burned out of control for several days after the earthquake. The fault has
produced seven earthquakes with a magnitude of more than ‘7’ on the Richter
Scale since 1939.
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