Earthquakes…

What are earthquakes and where do they occur?

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

Why do earthquakes happen?

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

A seismograph

How can we measure earthquakes?

The largest earthquake ever recorded was in Chile. It measured 9.5 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

• http://www.iris.edu/seismon/

• http://www.earthquakes.bgs.ac.uk/recent_events/recent_events.html

Why do we get earthquakes in Britain?

• We actually have 50-60 small earthquakes every year!• These occur along ‘fault lines’ (cracks in the main plates deep

beneath the ground).• As our plate is moving very slowly to the east every now and

then there are small movements along faults. • The most Britain can expect to see, in terms of damage, is

chimney pots falling down and windows cracking.

Why don’t we ever get BIG earthquakes?

Because we are not near a plate boundary but inside the Eurasian plate.

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

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.

Your task:

1. In your own words, explain why earthquakes happen (include a diagram). What type of plate boundary are they mainly found at?

2. What are the focus and epicentre? Draw a diagram to illustrate this.

3. What are seismic waves?4. What instrument do scientists use to measure the

strength and duration of an earthquake? Explain how it works.

5. What is the richter scale?6. What was the largest earthquake ever recorded?

Where was it?

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?

DROP COVER HOLD-ON…

• http://news.bbc.co.uk/1/hi/world/americas/7726924.stm

http://www.youtube.com/watch?v=j8mUZFeMwhE

http://www.youtube.com/watch?v=bAHNhtRT50A earthquake drill at school

• http://news.bbc.co.uk/1/hi/world/americas/7726031.stm simulation

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

deep foundations

strong lintels

overlapping bricks

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’?

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…

Your task…

7. How can we limit earthquake damage? Mention ways of predicting, planning and protecting.

8. What is the best shape for a building in an earthquake zone? Draw a diagram. What other measures can be taken to protect a building?

9. What should people do in an earthquake? Design a poster to be put up in public buildings, informing people what they should do.

10. What’s the Mercalli scale? Divide a page into 12 boxes and illustrate the twelve stages.