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    This module is included inLens: Siyavula: Social Sciences (Gr. 7-9)
    By: SiyavulaAs a part of collection: "Geography Grade 7"

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Earthquakes

Module by: Siyavula Uploaders. E-mail the author

SOCIAL SCIENCES: Geography

Grade 7

NATURAL HAZARDS

Module 4

Earthquakes

1. The occurrence and cause of earthquakes

A scientist who had experienced a powerful earthquake told of how it seemed to him as if the whole world had become a carpet that was given a good shake and was laid down again. People, buildings, mountains – everyone and everything seemed to have become mere dust on the carpet.

[From: Die Huisgenoot - Jongspan, 21 May 1987]

You need to remember that the earth’s crust consists of large, flat plates of rock. They are kilometres thick and drift on the dense, warm mass of magma of the mantle. The movement is very slow, so it cannot be perceived. The layers of rock that are closer to the mantle are hotter and melt more readily. Nearer the surface of the earth, the layers of rock are cooler and therefore harder.

Where the plates of the earth meet, they collide or slide against one another. Because of the shifting of the layered rock, they may bend or fold and even break like a plank that is broken in two. The earth’s crust is able to withstand the stress and pressure that is built up because of the movement from within. When it reaches a point at which it cannot accommodate the pressure by bending or folding, it cracks and breaks. Then there is a shift in the layers of rock and people perceive it as an earthquake.A fault line occurs which is even visible at the earth’s surface.

An earthquake is felt for a few minutes only, but after-shocks may occur for a while afterwards.

The well-known San Andreas fault runs through San Francisco in the American state of California. Millions of people live in this area, and are aware of this threat.

Figure 5 shows how the large rock plates move past one another very slowly (5 – 7 cm per year). When the sides hook onto one another, the stress increases. The rocks suddenly move and start to break off. The result – an earthquake occurs.

Figure 1
Figure 1 (graphics1.png)

Figure 6

The strength of an earthquake is measured by a seismograph

Activity 1:

To build a model of an earthquake

[LO 2.1, 2.3]

Making a model of an earthquake: Work in groups.

  1. Obtain two equally thick wooden boards. Place them alongside one another. Use cardboard to make building blocks that can be used to represent bricks, houses or buildings. Place these blocks in position over the fault line (where the two wooden boards touch one another). Now draw the boards away from one another or slide them past each other in opposite directions.

Figure 2
Figure 2 (Picture 3.png)

2. Explain what exactly happened to the blocks?

3. What are the names of the different parts of the earth’s crust (represented by the wooden boards)?

4. What would you suggest for making buildings more Earthquake proof? Discuss this in your group and report your suggestions to the class.

Where do most earthquakes occur?

Earthquakes mainly occur at the margins of ground-plates, which is where these plates are slowly moving towards or away from each other. The movement causes earthquakes to occur in the countries that lie above the margins of the plates, while countries that lie towards the centres of the plates are not seriously threatened by earthquakes.

South Africa is situated in the centre of a ground-plate; therefore we may not necessarily experience very serious earthquakes. But the stirrings in the mantle of the earth’s crust are noticeable in South Africa, as we have experienced in 1969 when an earthquake in the Boland caused much damage in Ceres.

In the next learning unit the map will show that earthquakes and volcanoes occur at the same places.

(See figure 8)

Activity 2:

To indicate on a map of the world in which areas earthquakes occur

[LO 2.1, 2.2]

2. The effect (consequences) of earthquakes on the lives of people and socio-economic activities

Read the magazine article that follows.

You are simply strolling down the street in the city or town where you live. Suddenly the ground around you starts to buckle and form waves like those that form in a dam into which a stone is hurled.

An awful droning, almost like a lamentation, rises from the earth. Around you buildings collapse like houses built of cards and the street in front of you is bursting open as if made of strips of soft, torn cardboard.

Railway girders bend and tear, bridges collapse, dam walls break. People and cars tumble into the enormous gaping cracks in the earth. The cracks close up again and everything disappears forever. Everywhere bricks, concrete blocks, beams and pillars fall down on people who scramble left and right for a place of shelter that cannot be found.

Fires break out because electric cables and gas pipes are broken. Water rushes from burst pipes. Windowpanes lie shivered into razor-sharp splinters among the rubble, adding to the horror. A most dreadful natural disaster. Horror as humankind has known it since the earliest times. Earthquake!

Huisgenoot, Jongspan, 21 May 1987.

Such an earthquake is rated as a very serious disaster, but all earthquakes fortunately are not equally severe. There may be a tremor of the earth’s crust every thirty minutes, but only about 500 of them are actually felt in any year. Fortunately those that do great damage and claim thousands of lives are few and far between.

Trace the world map from figure 8 and indicate only the areas where earthquakes occur. Then colour it in red.

Activity 3:

To discuss the consequences of earthquakes

[LO 2.1, 2.2]

1. Read the magazine article attentively. Form groups for discussing the effects of earthquakes on:

a) People

b) Nature

2. Collect photographs, pictures and newspapers or magazine cuttings dealing with earthquakes. Bring it along to the class for a discussion session and use it to supplement the information in your notes.

3. Read the following paragraph dealing with Tsunamis and try to find pictures and additional information dealing with this natural phenomenon.

Tsunami – another result of earthquakes!

When rock on the ocean floor shifts unexpectedly, the overlying seawater is also affected and a gulf that can move at 800 km per hour develops. When the gulf reaches the shallower bays of coastal areas it is dammed up higher. It can reach heights of between 30 and 60 metres and can cause serious destruction by flooding and destroying harbours and towns along the coast.

3. Why some people are at a higher risk to be affected by tropical cyclones than others

If you look at the map of the world (figure 8 on p. 33) on which the ground-plates are indicated, you will notice that we find some of the world’s most densely populated areas in these danger zones. Should an earthquake occur, many lives could be lost.

In developed countries or regions like Europe, the USA and Japan an earthquake’s damage can be limited and losses minimised. Buildings, bridges and roads are built to resist the effect of earthquakes. The infrastructure in such countries are highly sophisticated and their health care and medical services are immediately available in case of emergencies.

It is different, though, in developing countries. Many people die and constructions are easily destroyed. Buildings are usually erected in the cheapest possible way and cannot withstand the force of an earthquake. Thousands are left homeless, hungry and injured. The poor infrastructure prevents that aid reaches them soon enough. Corpses start decaying and drinking water is polluted, spreading disease which increases the number of deaths.

Activity 4:

To discuss the reason why people live in areas where earthquakes occur

[LO 2.2]

1. Why do people decide to live in areas where earthquakes occur? Take some time to think about this and then give your own opinion.

2. Where would you hide if an earthquake struck in your environment?

4. Precautionary measures: managing risk and reducing risk

Can earthquakes be forecast?

Unfortunately, this is not always possible. However, the earth’s crust is intensively studied and sensitive instruments register the slightest movement in the crust.

Scientists use special methods and apparatus, e.g. seismographs, to study and forecast earthquakes. A seismograph can detect any movement in the earth’s crust. When foreshocks occur scientists are able to detect activity in the earth’s crust and issue warnings in time. Some satellites are also equipped to pick up movement in the earth’s crust.

There are also other non-scientific signs in nature that, if observed in time, could help to forecast an earthquake, e.g.

  • a sudden significant change in the level of groundwater (e.g. in wells);
  • the sudden strange behaviour of animals.

If earthquakes could be forecast in time, warnings to evacuate the danger zones could be issued and so loss of life could be limited. Whether all people listen to such warnings is an open question.

Remember – not all earthquakes can be forecast. Some happen suddenly, without any foreshocks or other signs.

Activity 5:

To list emergency measures in case of an earthquake

[LO 2.3]

Imagine that you live in an area where earthquakes occur frequently (where there is a weak place in the earth’s crust). Draw up a list of emergency measures that should be applied before, during and after an earthquake.

Copy the world map from Figure 8 and indicate the areas where earthquakes occur on your own map. Then use red to colour in these areas.

Assessment

Table 1
Learning Outcomes(LOs)
LO 2
GEOGRAPHICAL KNOWLEDGE AND UNDERSTANDINGThe learner will be able to demonstrate geographical and environmental knowledge and understanding.
Assessment standards(ASe)
We know this when the learner:
2.1 describes and explains how natural hazards such as volcanoes, earthquakes and flooding occur, and their impact on human lives and socio-economic activities [people and places];2.2 investigates and explains why some people face a higher risk than others with respect to natural hazards [people and resources];2.3 identifies how risks and hazards can be managed [people and the environment].

Memorandum

Activity 1:

  1. Constructing a model

The teacher must provide two wooden planks of equal thickness and 7 - 9 building blocks made from cardboard. Follow the instructions as set out in Learning Unit 4, page 5, to carry out the experiment.

  1. As the planks are drawn away from each other in opposite directions, the building blocks also start shifting. If the planks continue to move, the building blocks tumble down.
  2. The two wooden planks represent two different layers constituting the earth’s crust. See Figure 8.
  3. See cutting on earthquakes and the design of buildings and insert here to serve as memo. Learners may also give their opinions. **(See accompanying note for an answer.)

Activity 2:

Ask learners to trace the world map, using Figure 8. The teacher can also supply the learners with a world map (outline only). Learners indicate in red where earthquake areas are to be found on our planet.

Activity 3:

Many people die or are seriously injured;

Damages amounting to millions of rands occur;

Buildings collapse or severe damage is caused;

Tarred roads buckle and are ripped apart;

Bridges collapse;

Dam walls collapse or get damaged;

Fires break out because of electric cables and gas pipes that get amaged;

Power failures cause total blackouts;

Water streams from burst pipes and cause flooding and a shortage of fresh water;

Sewage pipes break and cause pollution, which cause health hazards;

Telephone connections are severed;

Mountain passes are blocked due to rock falls;

The country’s economy is severely affected. International aid is important for reconstruction.

  1. b) Nature:

River courses change as a result of shifts in the earth’s crust. Consequently the natural environment also changes;

Topsoil along the mountain slopes become undone and start sliding down the slopes. Human beings and buildings might be buried under the landslides;

The natural vegetation is therefore destroyed and it may take many years to recover. In the meantime the lack of vegetation on the bare slopes increases the chances of soil erosion.

Floods and destruction occur in low-lying areas if an earthquake has originated under the sea-bed, causing a tsunami.

  1. Learners bring photographs, pictures and newspaper cuttings on earthquakes to the classroom. They discuss these, adding some of the points to their notes.

3. Tsunami’s The Southern Asian tsunami of 26 December 2004.

Learners collect information on this.

See web page http://iri.Ideo.columbia.edu-lareef/tsunami

Activity 4:

1. Why do people live in these regions?

Earthquakes are not an everyday phenomenon. Some regions might experience an earthquake once in a lifetime. People therefore take a chance and hope that it will not occur again.

Many of the “endangered regions” are also important financial and industrial centres. There are many job opportunities and prosperity there. Financial implications are therefore important considerations.

Traditionally many generations have been living there (especially in developed countries) who do not move away easily.

2. What to do during an earthquake.

Advice is plentiful.

Leave the building immediately.

Move to the top storey immediately if you live in a high rise building so that the building does not collapse on you.

Avoid the lifts of tall buildings. You could be trapped in them.

Seek refuge under a concrete beam if available, otherwise under stealthy furniture such as tables.

Move to open fields immediately where there are no flying objects.

Activity 5:

1. Emergency measures before an earthquake

Listen to the radio or TV daily. If tremors in the crust of the earth are picked up, warnings will be transmitted immediately.

Always have a backpack ready containing fresh clothes, a blanket or warm clothing.

The following should also be included: a) fresh water

b) non-perishable foodstuffs

c) medicine

d) a flashlight

Always keep your personal documents ready.

2. Emergency measures during an earthquake.

Find a place of safety immediately or move to an open field.

3. Emergency measures after an earthquake.

Avoid snooping around in damaged buildings. Loose objects could fall and cause injuries.

Erect tent settlements for homeless people as temporary housing facilities until emergency personnel have completed their clearing up operations.

Erect temporary sewage and water supply points.

Erect temporary catering facilities.

Supply medical aid to people who have been injured.

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