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?Why do earthquakes happen?

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.

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Richter Scale

The Greek earthquake (June 1995) measured 6.2 on the Richter Scale.

How many times greater was the Japanese earthquake?

Focus Epicentre

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

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?

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

Imagine you live in Los Angeles, list what you should include in your emergency plan?

make an emergency plan

organise 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

This is San Francisco in the U.S.A. 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 ‘earthquakes proof’?

If the epicentre of an earthquake is at ‘a’, which settlement will become the more damaged? Give reasons for your answer.

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?

Activity

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

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.