Restless Earth
Global Distribution of Volcanoes and Earthquakes
If the exam asks you to describe the
pattern of earthquakes and volcanoes.
Map to show the location of volcanoes
around the world
This is a skills question not a knowledge
question – you should not use the word
‘because’. Simply say what you see:
 Volcanoes and earthquakes are not evenly
spread across the earth
 They both occur on land and in the sea
 They can occur together and
independently of each other
 They tend to occur in lines
 An examples of volcanoes and
earthquakes occurring in lines in along the
west coast of North & South America
Map to show the distribution of
earthquakes around the world
The structure of the Earth
The Earth is made up for four layers:
Diagram to show the structure of the earth
1. The crust – solid rock which is
between 0km and 80km thick
2. The mantle – made of molten rock
that flows like a liquid
3. The outer core – a liquid made up of
silicate, nickel and iron
4. The inner core – a solid made up of
nickel and iron. Up to 5500ºC
Map to show the worlds main plate
boundaries
The Mantle – convectional currents
The mantle causes plates to move. The mantle gets hotter the closer to the core it gets, due
to pressure. As it acts like a liquid, the hottest mantle rises towards to crust. As it rises, it
begins to cool, condenses and sinks back down towards the core, where the process repeats
itself. This causes convection currents. These convection currents either circle towards or
away from each other (as shown in the diagram). Currents that circle towards each other
cause the crust floating on top to move towards each other, whilst currents that move away
cause the crust on top to move away from each other. This is what causes plates to move.
The Crust
There are two types of crust; oceanic
and continental. Oceanic crust is made
up of basalt and is denser than
continental crust which is made of
granite and cannot be destroyed.
Types of plate boundaries
North American
plate
Creates shield
volcanoes
Eurasian plate
Magma from
mantle creates
volcanic island
arcs e.g. MidAtlantic Ridge
South American
plate (continental
crust)
The Nazca Plate
moves towards South
American plate and
is forced underneath
it (subducts). It is
oceanic crust, so is
heavier.
Violent volcanic
eruptions. Produces
composite volcanoes.
Hot liquid rock
(magma) rises
Hot liquidOceanic crust
rock
being forced
(magma) downwards
rises.
causes severe
earthquakes.
Pacific Plate moving
faster than the
North American
Plate
Rocks formerly on
ocean bed are
pushed together,
buckled and forced
up to form Himalayan
Mountains. They are
the same
weight/crust, so
neither plate is
subducted.
Indo-Australian
Plate (continental
crust)
Friction and
heat from
mantle melts
rock
North American
Plate moving
slower than, and
slightly
towards, Pacific
Plate
Pressure builds up and when it is suddenly release it
produces seismic waves and violent earthquakes
Collision margin
Eurasian Plate
(continental
crust)
Young Fold Mountains
Young Fold Mountains are mountains formed from
the folding of the earth's crust. Fold mountains are
formed when two plates move together (collision or
destructive plate margin). This can be where two
continental plates or a continental and an oceanic
plate move towards each other. The movement of the
two plates forces sedimentary rocks upwards into a
series of folds. Fold mountains are usually found
along the edges continents. This is where the
thickest deposits of sedimentary rock generally
accumulate. When plates and the continents riding on
them collide, the accumulated layers of rock crumple
and fold like a tablecloth that is pushed across a
table.
During long periods of quiet sedimentary rocks
formed from the build up of sediments deposited by
rivers into the sea (depression/geosynclines). Over
time these compressed together to form
sedimentary rocks. When the two plates collide
these rocks are forced upwards and fold upwards
(anticline) and downwards (syncline). In some places
the folds are pushed over on one side (overfolds).
Young Fold Mountains are 10 to 25 million years of age
e.g. Rockies, Alps and Himalayas.
Fold Mountains - The Alps
The Alps are home to eleven million
people and thus the most densely
populated mountain area in the world.
The economy of this region is based on
the exploitation of the coniferous
forest and pasturing dairy cattle, and
tourism plays an important role.
Tourism
HEP Schemes
Since the end of the WWII, the Alps
have become the winter and summer
play ground of European urban dwellers.
Hydroelectric power schemes are common in the
Alps. The combination of tectonic and glacial
processes make the area ideally suited for HEP
schemes. HEP schemes often involve many
different watersheds. It is an area of excess
water and deep U-shaped valleys. Since the
development of HEP at the end of the 19th and
the beginning of the 20th centuries these
valleys have been dammed and used to develop
HEP.
In winter the Alps are a very popular
destination amongst winter tourists. Ski
resorts such as Val d'Isere and Les
Deux Alps have been purpose-built.
These areas are very crowded in the
winter but tend to be quieter in the
summer. However, traditional ski
resorts tend to be busy throughout the
year.
In summer between June and
September the Alps are heavily
populated with walkers, cable-car riders
and paragliders.
The huge number of tourist visitors to
the Alps has led to them becoming the
most threatened mountain chain in the
world. This is in terms of its fragile
ecological and physical system.
The development of HEP in The Alps led to the
establishment in the lower valleys of electricitydependent industries, manufacturing such
products as aluminium, chemicals, and speciality
steels.
Farming and Forestry
Coniferous trees are the main trees forested in
the Alps. They are ideally suited to the Alpine
environment. Their conical shape makes the tree
stable in windy conditions. The downward
sloping, springy branches allows the snow to
slide of the tree without damaging its branches.
The wide meadows of The Alps make the area
ideal for sheep farming. In the more extreme
upland areas goat herding is the main type of
farming. The cold climate and difficult relief
make it almost impossible for arable farming to
occur.
Types of volcanoes
Shield
Composite
Constructive plate boundary
Wide base and gentle slopes
Made of layers of lava only
Regular and frequent eruptions
Runny lava with low silica content
Not very violent
Mauna Loa, Hawaii
Lava travels longer distances before cooling
Destructive plate boundary
Tall cone with steep slopes and a narrow base
Made of alternative layers of ash and lava
Irregular eruptions with long dormant periods
Thick lava with high silica content (viscous)
Violent explosions
Mount St. Helens
Lava may cool inside the vent – the next
eruption is very explosive to remove the plug
Mauna Loa Shield Volcano
Mt St Helens Composite Volcano
LEDC Case Study: Montserrat eruption, July 1995 – June 1997
Montserrat is a small island in the
Caribbean, and is still a British colony.
Many of the residents are quite poor,
practising subsistence farming. Before
the eruption, the population was 12,000.
50% of people lived in the capital,
Plymouth.
In July 1995, the Soufriere Hills
volcano erupted for the first time in
350 years.
Causes:
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The North and South American Plates
are being subducted under the
Caribbean Plate (Destructive)
The melted plate, mixed with sea
water, is less dense than the rest of
the mantle. So the melted magma
rises upwards
The dissolved gases are released when
the magma gets higher up. That’s
because the pressure is lower in the
crust.
The released gases pushed out the
dust and ash from previous eruptions.
That’s what made the first eruptions
in July 1995. And the volcano has
been active ever since.
Short term effects:
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Ashfall from the eruption has caused
severe disruption to life on the island.
In August 1995 people were evacuated to
the north of the island, and were forced to
live in halls and churches, sharing toilets,
with nothing to do. Others had to live in
makeshift shelters with inadequate
sanitation.
In April 1996 the capital city of Plymouth
was evacuated.
In June 1997 the south of the island was
covered by rivers of hot ash, gases, mud
and rock, known as PYROCLASTIC FLOWS.
These caused huge fires, killing 19 people.
The long term effects
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The country’s tourist industry ground to a halt.
The ports and airport had to close, restricting trade and affecting Montserrat’s economy.
Two-thirds of Montserrat’s homes and three-quarters of its infrastructure (roads,
telephone lines, etc.) were lost due to ashfall or fire.
Two-thirds of Montserrat’s homes and three-quarters of its infrastructure (roads,
telephone lines, etc.) were lost due to ashfall or fire.
Short term responses/solutions
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Scientists monitored the volcano and set up warning systems
UK government sent £17 million of emergency aid
Red Cross set up temporary schools
People evacuated to the north of the island and then to other countries. Some went on
boats paid for by the UK and USA. The British navy took some people. By November
1997 the population had fallen to 3500.
USA sent troops for the evacuation
Charities also sent emergency food for farm animals.
Long term responses/solutions
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By 2005, the south of the island was still out of bounds and scientists were still
monitoring the area.
People have now been allowed to move back further north. By 2005 the population was
over 8000.
Red Cross built a home for the elderly
The UK government, at a cost of £122.8 million, funded a three-year redevelopment
programme for houses, schools, medical services, infrastructure and agriculture.
People were also offered mortgages to start new businesses.
The population structure changed, because more of the younger people made new lives
elsewhere, and more of the elderly had either not left in the first place, or returned.
Some vegetation began to re-grow in the south of the island. The soil will eventually
become fertile as the ash and lava break down.
Tourists may come back and the volcano itself may become a tourist attraction.
MEDC Case Study: Mount St. Helens eruption, 18th May 1980
Causes:
 20 March 1980 there was an earthquake
under the mountain, caused by the magma
beginning to move.
 More earthquakes followed in the days
afterwards
 27 March, gas and steam belched out of
the top of the mountain.
 3 April, a bulge started to appear on the
side of the mountain, and continued to
grow. By 12 April it was 100 metres high.
 On May the volcano erupted out of its side
and top. A pyroclastic flow occurred,
moving at 300 km per hour.
Mount St. Helens is a volcano in the
Cascade Mountain Range in the USA.
They are FOLD MOUNTAINS on a
destructive plate boundary.
Long term effects
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The area is now a tourist attraction.
This means the local economy is
wealthier than it was before the
eruption.
There is now an increased risk of
flooding due to ash and mud blocking
river valleys.
Short term effects
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The pyroclastic flow flattened and burnt trees over 360 square km. 7000 animals were
killed in the forests. 12 million salmon in a fish farm were killed. 61 people died, mainly
scientists and photographers.
Hot magma melted the snow on the mountain, causing mudslides which flowed down river
valleys at 35 metres per second.
A cloud of smoke, dust and ash went upwards and made a cloud 24 km up into the sky.
Planes had to be diverted. Roads became unusable and destroyed crops and farm
machinery. This cost of the damage caused by the ash was $175 million.
After the eruption, the mountain appeared very different. The side had blown out and
the top had collapsed. It was 365 metres lower than it used to be!
Responses:
Short term - Prior to the main eruption, scientists issued warnings to the local people that
they might have to evacuate the area. On 30 April scientists gave another warning and the
local authorities put a 30 km danger zone around the volcano that people were not allowed to
enter.
Long term - The US government gave $951 million in aid to rebuild industry in the area and
compensate people.
Supervolcanoes
Supervolcanoes occur on a much bigger scale than normal volcanoes. They emit at
least 1000km³ of material compared to a normal volcanoes such as Mount St. Helens
which only emitted 1km³. They can occur away from plate boundaries, whereas
normal volcanoes only occur on destructive or constructive plate boundaries.
Supervolcanoes do not look like normal volcanoes with its cone shape; they have large
depressions called calderas with a rim of higher land around the edges.
Yellowstone
Yellowstone is in Montana, in the USA. Yellowstone is a hot spot, where plumes of
magma rise towards the earths crust. The last eruption of Yellowstone was 630,000
years ago. Its caldera is 80km long, 40km wide and 8km deep. There is evidence that
the magma beneath Yellowstone is shifting, the caldera is bulging up near Lake
Yellowstone. The ground has risen in places by 70cm.
If an eruption occurred it would…
 Destroy 10,000km² of land
 Kill 87,000 people
 15cm of ash would cover buildings with 100km
 1 in 3 people affected would die
 Ash would affect transport link, farming and
electricity/water supplies
 Mud flows would occur
 The UK would have ash falling over the country after
five days
 Crops would fail as sunlight is blocked out by the ash.
 2,000 tonnes of sulphuric acid would be ejected into our
atmosphere and this would deflect sunlight back into
space and would trigger a catastrophic volcanic winter
which could results in temperatures decreasing between
12ºC and 16ºC. This could cause monsoon rains to fail
and ultimately lead to mass starvation.
This is Old Faithful
Geyser. A geyser is when
water erupts into the air
under pressure.
Earthquakes
What is an earthquake?
Earthquakes usually occur at plate boundaries. Powerful forces from inside the earth
(convections currents) cause each plate to move in a different direction to its
neighbour. The rock stores up the energy as strain energy. Eventually, the pressure
gets too much. One mass of rock gives way and slips. The stored energy is released in
waves called seismic waves. These waves get weaker as they radiate away from the
epicentre.
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The focus of the earthquake is the point where the waves started.
The epicentre is the point directly above it on the Earth’s surface.
As the rock settles into its new position, there will be lots of smaller
earthquakes called aftershocks.
Measuring earthquakes
Earthquakes are measured using
machines called seismometers. These
record the shaking as waves on a
graph. This can tell scientists how
much energy the earthquake gave out.
This is known as the earthquake’s
magnitude. It can be shown on the
Richter Scale.
The Richter Scale
An increase of 1 on this scale means the shaking is 10 times
grater, and about 30 times more energy is given out.
Richter
scale no.
No. of
earthquakes per
year
< 3.4
800 000
3.5 - 4.2
30 000
4.3 - 4.8
4 800
Most people notice them, windows rattle.
4.9 - 5.4
1400
Everyone notices them, dishes may break, open doors swing.
5.5 - 6.1
500
Slight damage to buildings, plaster cracks, bricks fall.
6.2 6.9
100
Much damage to buildings: chimneys fall, houses move on foundations.
7.0 - 7.3
15
Serious damage: bridges twist, walls fracture, buildings may collapse.
7.4 - 7.9
4
Great damage, most buildings collapse.
> 8.0
One every 5 to
10 years
Typical effects of this magnitude
Detected only by seismometers
Just about noticeable indoors
Total damage, surface waves seen, objects thrown in the air.
The Mercalli Scale
The Mercalli Scale (below) is less widely used, but is another method of describing the
strength of an earthquake. The problem with it can be that it describes the EFFECTS of
the earthquake and not the magnitude itself. The effects of two earthquakes of identical
magnitude would differ greatly if one earthquake occurred in an MEDC and one in an LEDC
due to differing building standards and hazard preparation and response between the two
countries.
Mid-plate earthquakes
Whilst most major earthquakes occur along plate boundaries, there are some which
do not. We call these mid-plate earthquakes. There are four main reasons for these
earthquakes:
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Underground subsidence following deep mining.
Lubrication of an ancient fault by moving water or oil.
Dam and reservoir construction, partly due to the increased pressure exerted
on a fault from above and also the likelihood of water seeping into the
groundwater zone and lubricating a fault.
Scientists now believe that extreme pressures exerted at plate margins
actually cause a web of cracks to form right across the plate, rather like a
windscreen that crazes when hit by a stone. This means that marginal tensions
can be released mid-plate as well as at the plate margin itself.
MEDC Case Study: Kobe earthquake, 17th January 1995
LEDC Case Study: Kashmir Earthquake, 8th
October 2005
Where and when? 8.40am on 8 October, 2005.
A massive earthquake hits Kashmir in Pakistan.
It’s focus is 26km down. It measures 7.6 on the
Richter scale. The shaking lasts for 60 seconds.
Aftershocks (some up to 6 on the Richter scale)
continue for 2 days.
Why? Kashmir is on the border of India and
Pakistan, in a mountainous area (part of the
Himalayas). This area is where two plates are
colliding, at a COLLISION PLATE BOUNDARY. The Indian plate is colliding with the
Eurasian plate.
Short term effects:
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Buildings collapsed, signs fell of walls,
windows shattered, furniture fell over,
roads cracked and bridges toppled.
These caused injury and death.
In Kashmir, over 70,000 people were
killed, 100,000 were injured and 3.3
million homes were destroyed.
Landslides also occurred.
The effects were so severe because
buildings in the towns were not built
very strongly.
As Saturday is a normal school day in
the region, most students were at
school when the earthquake struck.
Many were buried under collapsed
school buildings.
Water pipes broke, and people did not
have a clean water supply. This caused
diseases like cholera and typhoid to
spread, which again caused more deaths.
People also developed respiratory
infections like pneumonia. There were
also deaths from cold in the harsh
winter, as they only had thin tents to
sleep in.
Long term effects:
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In the urban areas, many people lost their
jobs as their offices or shops were
damaged.
Electricity lines were brought down, so
reconstruction was made harder.
Schools were damaged, and students lost
their books, negatively affecting their
education.
3.3 million people lost their homes and
were forced to live in temporary shelters
until rebuilding could start in the spring.
The overall cost of the damage is
expected to be over $5 billion.
Immediate responses:
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Local people started trying to rescue those who were trapped
The Indian Red Cross distributed 21 500 blankets, 300 kitchen sets and medical supplies.
The army and emergency services arrived to help did people out.
Helicopters from the military were used to take the injured to first aid centres on
flatter ground.
The border between India and Pakistan was opened in a few places to allow food
emergency supplies to cross.
Tents were given out by charities like Muslim Aid and the Pakistani and Indian armies.
Pakistan Airways carried emergency food and supplies from other countries for free.
Military hospitals were opened for civilian casualties.
Rescue and medical teams arrived from other countries (eg Russia and the UK) to try to
find survivors and treat the injured.
Long term responses:
 The Red Cross re-established water supplies in Muzaffarabad.
 The tents weren’t enough for the cold winter, so the army and the Red Crescent built prefabricated homes using corrugated tin for people to live in until they had rebuilt their
houses.
 Schools will need to be re-built and re-supplied.
 Teachers may be trained in counselling to help traumatized children.
 Sanitation will be needed for the temporary houses.
 Building laws will be tightened up to make sure that next time there will be less damage
and fewer deaths.
Tsunamis
Tsunami
Normal wave
Tsunamis are triggered by earthquakes. A Tsunami is a special type of wave where
the entire depth of the sea or ocean is set into motion by an event, normally an
earthquake, which displaces the water above it and creates huge waves. In deep
water, the waves move at high speed, but when they reach shallower water near the
coast, they begin to slow down but build in height. A normal wave is created by wind
only moving the surface water not the whole volume of the sea/ocean.
Asian Tsunami/Indian Ocean Earthquake, 26th December 2004
On the 26th December 2004 the Indo-Australian plate subducting under the Eurasian
plate moved (destructive plate margin) causing an earthquake measuring 9.3 on the
Richter scale (some measured it at 9.1).
It was one of the worst disasters in history killing nearly 300,000 people, 650,000
were seriously injured and up to 2 millions were made homeless. Public buildings were
wiped out and many people posted photos of loved ones in hope of trying to find them.
Identification of the dead was a major problem. Rescue and emergency services were
swamped by the disaster. Injured people were untreated for days and bodies
littered the streets before being buried in mass graves
Indonesia:
Sri Lanka:
Thailand:
236,169 people died. Western
Sumatra was the closest
inhabited area to the
earthquake’s epicentre and was
devastated. UP to 70% of some
coastal populations were killed or
missing. At Banda Aceh the wave
reached nearly 17 metres high.
The southern and eastern
coastlines were ravaged,
with homes, crops and
fishing boats destroyed.
400,000 people lost their
jobs and 31,147 people
died. The wave reached
6m high in places.
The west coast was
severely hit, including
the islands like Phi Phi
and Phuket, the dead
there included 1700
foreigners from 36
countries.
Immediate responses
 Fresh water, water purification tablets, food, sheeting and tents arrived from
international communities.
 $7 billion was donated worldwide to the affected countries.
 People in the UK donated £372 million and the government promised £75 million in
aid.
 The UN’s World Food Programme provided food aid for more than 1.3 million
people
Long term responses/solutions
 The Disasters Emergency Committee (DEC) spent £230 million on rebuilding
projects in Sri Lanka and Indonesia.
 The Indian Ocean Tsunami Warning System was set up in June 2006 so that
people know how to respond and so that local authorities have plans in place should
another tsunami occur. Warnings go out via radio, TV, email, bells & megaphones.
 The Green Coast Project in Aceh, Indonesia are restoring and replanting mangrove
swamps which help protect against tsunamis. They absorb the wave’s power
naturally. This has also helped to provide a livelihood for people as they are a
good breeding ground for fish as well.
Why do people choose to live in tectonic areas?
Earthquakes:
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Economic: People work in the area and can’t afford (or don’t want to) lose their jobs by
moving. Los Angeles, for example, is a rich city with (for most people) a good lifestyle
and well-paid jobs.
Technological: People feel secure that prediction will give them enough warning and,
even if it doesn’t, that technology will mean their homes are safe and the emergency
services will be able to cope.
Perception: People don’t see relatively uncommon earthquakes as big risks. Regular
things like car accidents and crime are often seen as being more likely to happen to
you, so are more ‘dangerous’.
Social: People have their families, friends, schools and favourite places nearby, and
don’t want to lose them.
Volcanoes:
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Fertile soil when the lava weathers
Tourist attractions, e.g. trips to the rim of the crater, hotel accommodation, souvenir
shops.
Minerals, e.g. sulphur, borax and pumice.
Lava flows build new land, e.g. Iceland, Hawaii.
Hot springs for bathing, heating.
Heat used to generate electricity.
Managing tectonic hazards
It's not possible to prevent earthquakes and volcanic eruptions from happening, but
careful management can minimise the damage that they cause. Prediction is the most
important aspect of this, as this gives people time to evacuate the area and make
preparations for the event. It is often LEDC countries that are hardest hit by the
impact of earthquakes and volcanoes.
Predicting and preparing for volcanoes
Unfortunately there is nothing that can be done to stop volcanic eruptions or
earthquakes. Prevention is not an option. This leaves two possible ways of managing
hazards such as earthquakes and volcanoes:
1. prediction
2. preparation
Predicting eruptions
As a volcano becomes active, it gives off a number of warning signs. These warning
signs are picked up by vulcanologists (those who study volcanoes) and the volcano is
monitored. The key techniques for monitoring a volcano are outlined in the table
below.
Eruption detection and monitoring
Warning signs
Monitoring techniques
Hundreds of small earthquakes are caused as
magma rises up through cracks in the Earth's
crust.
Seismometers are used to detect
earthquakes.
Temperatures around volcano rise as activity
increases.
Thermal imaging techniques and satellite
cameras can be used to detect the heat
around a volcano.
When a volcano is close to erupting it starts to
release gases. The higher the sulphur content of
these gases the closer volcano is to erupting.
Gas samples may be taken and chemical
sensors used to measure sulphur levels.
As technology improves, the techniques available for predicting and monitoring
volcanic activity are becoming more and more accurate. Volcanoes such as Mt. St.
Helens in the USA or Mt. Etna in Italy are closely monitored at all times. This is
because they are active or have been active in recent years. This means that people
can benefit from early-warning signs of an eruption. However, as well as prediction,
people need to be prepared for an eruption.
Preparing for an eruption
A detailed plan is needed for dealing with a possible eruption. Everyone who could be
affected by the eruption needs to know the plan and what they should do if it needs
to be put into action.
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Planning for a volcano includes creating an exclusion zone around the volcano
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Being ready and able to evacuate residents
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Having an emergency supply of basic provisions such as food
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Funds need to be available to deal with the emergency and a good
communication system needs to be in place
Predicting earthquakes
Earthquakes are not as easy to predict as volcanic eruptions. However, there are still
some ways of monitoring the chances of an earthquake:
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Laser beams can be used to detect plate movement.
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A seismometer: A machine that detects vibrations in the earth's crust is used
to pick up the vibrations in the Earth's crust. An increase in vibrations may
indicate a possible earthquake.
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Radon gas escapes from cracks in the Earth's crust. Levels of radon gas can be
monitored; an increase may suggest an earthquake.
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Many of the prediction techniques used to monitor earthquakes are not
considered 100% reliable. Planning and preparing for an earthquake is
therefore very important. As with volcanoes, there are many ways of preparing
for an earthquake. These are outlined in the table below.
Preparing for earthquakes
Preparation Explanation
People living in earthquake zones need to know what they should do in
the event of a quake. Training people may involve holding earthquake
drills and educating people via TV or radio.
People may put together emergency kits and store them in their homes.
An emergency kit may include first-aid items, blankets and tinned food.
Earthquake proof buildings have been constructed in many major cities
e.g. The transamerica Pyramid in San Francisco. Buildings such as this
are designed to absorb the energy of an earthquake and to withstand
the movement of the Earth.
Roads and bridges can also be designed to withstand the power of
earthquakes.
Earthquakes and volcanoes in LEDCs
Less Economically Developed Countries (LEDCs) often suffer more from the effects
of volcanoes and earthquakes than More Economically Developed Countries (MEDCs).
This is because LEDCs have weaker communication systems, lower standards of
building, together with limited funds to deal with either evacuation before the
disaster, or to deal with the aftermath of the emergency. See the diagram below.