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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 place s.

(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.

Questions & Answers

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At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
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Source:  OpenStax, Geography grade 7. OpenStax CNX. Sep 09, 2009 Download for free at http://cnx.org/content/col11021/1.1
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