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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?What is a tsunami?

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What are earthquakes?

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.

CONSERVATIVE

DESTRUCTIVE


Destructive Plate Boundary


Conservative Plate Boundary



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Why do earthquakes happen?



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How can we measure earthquakes?

The largest earthquake ever recorded was in Chile. It measured 8.9 on 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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Richter Scale

The Richter Scale


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 many times greater was the Japanese earthquake?

How can we measure earthquakes?

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Richter Scale


A seismograph


Mercalli Scale

This measures how much damage is caused by the earthquake based on observations. It is measured on a scale between I and XII.

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.VII Specially designed structures damaged slightly, others collapsed.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, objects are tumbled and tossed.

Activity

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



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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

1. 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?


2. plan

What should people pack in their emergency kit?

make an emergency plan

organize regular ‘earthquake practices’ for offices and schools

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)

enforce regulations to make some buildings earthquake proof

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

How can we limit earthquake damage?


This is San Francisco in the USA. Why does this skyscraper have a wide base?


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’?

Buildings in earthquake zones


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’?

Sky’s the limit!


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.

What they did…


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 teams carry on searching for up to 72 hours after a disaster, but it has been known for people to survive much longer than this. The longest survival is 17 days by a Korean who chewed cardboard and drank his own urine before being rescued.

Fact File (3 days after the

earthquake)

Dead : 10,059Missing : up to 35,000Injured : over 45,000


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 hospital to look after injured

Search for more survivors

Bury the dead Stabilize the damaged buildings

Organize emergency camps and supplies for the survivors

Turkish earthquake (August 1999)


Factors affecting the damage caused by earthquakes

size of the earthquake

time of day

emergency services

building design and construction

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?


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?

size of the earthquake

time of day

emergency services

building design and construction

GNP (wealth)

number of deaths

education

Los Angeles Turkey


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.

Los Angeles earthquake (1/94)


Turkey earthquake (8/99)

Izmit buildings substandardThe 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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SE Asian tsunami – December 2004

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.


Where was the tsunami?


What caused the tsunami?

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