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Earthquakes

As part of your GCSE geography studies of how the Earth actually works, you will be required to study earthquakes. Not only do you need to know what causes them, you need to know how they affect human lives in both rich and poor countries. You may be challenged to examine information from geographical information systems in order to draw conclusions from the data.

The Earth is made up from a number of different layers, the core, the mantle and the crust. The crust is cracked into large plates which move slowly. It is believed that convection currents in the upper mantle causes this to happen. The movements are measured in centimetres per year but, because the plates are massive, the forces involved with their movements are enormous.

Where these plates come together, various things can happen.

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One thing is for certain, one of the plates must be pushed back down into the mantle. This process only stops when the plates become completely welded together, forming a mountain range like the Alps or Himalayas. This is called a destructive boundary as one of the plates is destroyed. As one plate descends beneath the other, the movement is not smooth. The plates lock together, so strain builds up in the locked portion. When the strain is greater than the strength of the rocks, they break and movement resumes. The strain is released as a series of shockwaves travelling through the crust. This is what we know as an earthquake.

The shockwaves from a large earthquake can be very destructive when they reach the surface of the Earth. Compared to a LEDC, a MEDC that has been hit by an earthquake will usually suffer less damage and less loss of life in the main towns and cities since they have the money to build earthquake resistant buildings.

The earthquakes that are produced at destructive plate boundaries occur deep in the crust. Where plates slide past each other, it is known as a conservative boundary. Again, the plates do not move smoothly. They lock together for decades or even centuries but the plates keep moving. When the rocks break under the accumulated strain, a shallow earthquake occurs. These too can be extremely destructive. At constructive plate boundaries, as the plates move apart, the rocks between them break which can also be a cause of shallow earthquakes.

Even though the UK is not on a plate boundary, we still get earthquakes, but very small ones. Despite that, they have been known to damage older or weaker houses. These are thought to occur when there is a slight movement of an old fault line - fault lines are where the rocks have been broken by Earth movements in the past.

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  1. Which of the following is a secondary effect of an earthquake?
    Earthquakes cause the ground to shake and cracks can appear. Secondary effects are events that are triggered by an earthquake such as landslides, falling objects, fires and disease (water supplies are broken, so there is little or no clean water for hygiene and drinking)
  2. The movement of the Earth's plates past one-another is ...
    There is a lot of friction between the rocks of the plates so they don't move smoothly past each other. This movement is unpredictable which is why earthquake forecasting is so difficult
  3. Japan suffers from large earthquakes because ...
    The Pacific plate is being destroyed under Japan
  4. Where do earthquakes mainly occur?
    They are mainly caused by plates moving against each other
  5. When compared with a LEDC, during a large earthquake, the buildings in a city of a MEDC ...
    MEDCs can afford to build earthquake resistant buildings
  6. Which of the following is not a reason why there is greater loss of life in a LEDC than a MEDC from an earthquake measuring 8 on the Richter scale?
    There are many reasons why populations in LEDCs or less developed regions of MEDCs are hit harder - it usually comes down to a lack of money
  7. The point on the surface of the Earth, directly above where the earthquake originates is known as the ...
    The point where the earthquake happened is known as the focus
  8. On the following list, where is the deepest earthquake likely to occur?
    You should be aware of the main examples of the different types of plate boundary. You should also know that deep earthquakes occur at destructive plate boundaries. The west coast of Peru is where you find a destructive plate boundary
  9. The cause of an earthquake is ...
    There is a huge amount of friction between the plates which stops them moving smoothly
  10. Which one of the following explains why we have small earthquakes in Britain?
    Even though the faults were made millions of years in the past, the rocks on either side can still move a little, creating small earthquakes that are sometimes called earth tremors

Author: Kev Woodward

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