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Earthquakes


What are earthquakes and where do they occur?What causes earthquakes?How are earthquakes measured?What is the difference between the epicentre and the focus?How can we limit the damage caused by earthquakes?Pakistan earthquake – October 2005What is a tsunami?

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They can occur at all four major plate boundaries but the most severe earthquakes are normally found at conservative and destructive plate boundaries.

conservative destructive

Earthquakes are vibrations caused by earth movements at plate boundaries and at major fault lines (cracks in the earth’s surface).

What are earthquakes?


Destructive plate boundary


Conservative plate boundary



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Why do earthquakes happen?



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This measures the magnitude of a tremor (how powerful it is) using an instrument called aseismograph. On the Richter Scale, magnitude is expressed in whole numbers and decimal fractions. Although the Richter Scale has no upper limit, the largest earthquake ever recorded was in 1960 in Chile. It measured 9.5 on the Richter Scale.

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’.

The Richter Scale

How can we measure earthquakes?


How many times greater was the Japanese earthquake?

The Japanese earthquake was 10 times more powerful than the Greek earthquake.

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.

How can we measure earthquakes?


A seismograph


Mercalli Scale

The Mercalli scalemeasures how much damage is caused by the earthquake based on observations.

It is measured on a scale between 1 and 12.

Mercalli Scale


I Felt by almost no one.II Felt by very few people.III Tremor noticed by many, but they often do not realise it is an

earthquake.IV Felt indoors by many. Feels like a truck has struck the building.V Felt by everyone; many people are awakened. Swaying trees and

poles may be observed.VI Felt by all; many people run outdoors. Furniture is moved.VII Everyone runs outdoors. Poorly built structures considerably damaged.

Slight damage elsewhere.VIII Specially designed structures damaged slightly, others collapse.IX All buildings considerably damaged, many shift off foundations.

Noticeable cracks in the ground.X Many structures destroyed. Ground badly cracked.XI Almost all structures fall. Bridges wrecked.XII Total destruction. Waves seen on ground surfaces.

Design your own cartoon based on the Mercalli Scale descriptions below.

Activity



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The focus is the point at which the rock moves. Seismic waves start at the focus.The epicentre is directly above the focus on the earth’s surface.

Epicentre and focus


Epicentre and focus


Focus

Epicentre

An earthquake has occurred along this fault line. Match the letter with the correct label.

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?

Epicentre and focus


If the epicentre of an earthquake is at ‘A’, which settlement

will be damaged the most? Give reasons for your answer.

Epicentre and focus



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predict plan protect

Predict

water levels can rise in wells and lakes because of cracks in the rock

foreshocks before the main quake can be detected by a seismometer

animals can act strangely before the earthquake

a tiltmeter can check any movement within the rocks

How can we limit earthquake damage?


Plan and protect



What should people pack in their emergency kit?

Design a poster reminding people what to do in an earthquake.

Plan and protect



What other measures would make buildings less likely to collapse in an earthquake?

Building regulations in earthquake zones


Which shape of building would be most ‘earthquake proof’?

Explain your answer.

Buildings in earthquake zones


This is San Francisco in the USA.

San Francisco is near the San Andreas Fault and therefore the city experiences earthquakes.

This skyscraper has been built to be ‘earthquake-proof’.

Its wide base lowers the centre of gravity of the building and makes it more stable.

Building in earthquake zones


This is Sky Tower in Auckland, New Zealand.

Sky Tower is the tallest tower (328 metres) in the Southern Hemisphere. It weighs 21 million kilos (20,000 tonnes), which is equivalent to 6,000 elephants!

Auckland is in an earthquake zone and so the tower is constructed from a high strength, high performance concrete.

Sky Tower's foundations go down more than 15 metres.

Sky’s the limit!


size of the earthquake

time of day

emergency services

building design and construction

education

physical landscape

1) Which factor/s do you think is/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?

Factors affecting the damage caused by earthquakes


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).

size of the earthquake

time of day

emergency services

building design and construction

GNP (wealth)

number of deaths

education

Los Angeles Turkey

Factors affecting the damage caused by earthquakes


Los Angeles earthquake (1/94)


Turkey earthquake (8/99)



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On the 8th October 2005, a devastating earthquake hit Pakistan.

The devastation was huge. Expertsbelieve the damage will take decades to repair.

The earthquake registered 7.6 on the Richter Scale.

Pakistan earthquake


More than 87,000 peopledied in the earthquake.It is believed that tensof thousands were injured.

3 million people were left homeless. Most of these had to struggle through the cold winter months in basic tents. It was only thanks to help provided by the government and aid agencies that thousands more did not die from cold or disease.

Effects of the earthquake


Pakistan lies to the west of India and is on a collision plate boundary between the Indian plate and the Eurasian plate. Millions of years ago, these twoplates collided to produce the Himalayas.

The Indian plate is still moving into theEurasian plate at a rate of 67 mm per year.This is causing the mountains to risehigher as well as producing earthquakes.

Click play to see the effecta collision plate boundaryhas on the landscape.

Why do earthquakes occur in Pakistan


One of the reasons why therewas so much devastationwas the poor quality of the buildings in the area. Many of the village buildings were made from stones laid togetherusing low-grade cement,mud or sometimes even laid dry.

Pakistan is not a rich country and most people did not have the money to build expensive, high-quality structures. 60% of the buildings in the towns were made from cheap stone masonry blocks, held together by low-grade mortar. Over half of these buildings collapsed in the earthquake, causing most deaths.

Causes of devastation


Richer, industrialized countries have been able to employ advanced building techniques to minimizethe devastation caused by earthquakes. These techniques are very expensive. High demand for housing in Pakistan and poor economic conditions, has meant most houses have been poorly constructed often by the occupants themselves.

However, since the earthquake, the Pakistani government hasintroduced a new building code. It includes designs and details about how to make buildings more resistant to earthquakes.

Earthquake proofing


Due to the remote locationof the earthquake, many people were left stranded without help.

Aid agencies and the Pakistani government needed to get emergency aid to people using helicopters.

Emergency aid is short-term, it aims to supply people with the essentials they need to survive. Aid agencies have to prioritize what type of aid is the most urgently needed.

Earthquake aid


Earthquake aid


Rebuilding will offer Pakistan the chanceto improve the quality of its schools and hospitals by building safer and better equipped structures but long-termrecovery will be a very slow process.The devastating impact of the earthquake will have many long lasting effects on this region.

The Pakistani government promised money to those that losttheir homes. However, rebuilding after an earthquake can bedifficult as often there is little infrastructure, tools arein short supply and there are few suitable sites for building.

The future for Pakistan



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Tsunamis are tidal waves triggered by underwater earthquakes. The rate of travel of a tsunami is between 400-600 miles per hour.

The tsunami in SE Asia occurred on the 26th December 2004. The earthquake measured 9.0 on the Richter Scale and occurred off the northern tip of Sumatra. The tsunami spread across the Indian Ocean and hit coastal areas of Sri Lanka, India, Bangladesh, Myanmar, Indonesia and Malaysia. The death toll is believed to be 290,000.

SE Asian tsunami – December 2004


Where was the tsunami?


What caused the tsunami?

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