Earthquakes - Example Answers
1. Describe the location of the worlds major earthquake zones and explain why earthquakes occur in these zones. (10 marks)
Earthquakes occur in long narrow belts(1) where tectonic plates meet (1). The largest belt runs around the Pacific Ocean and is called 'The Pacific Ring of Fire'(1). These are two reasons why earthquakes are common here:
1. Part of the west coast of the Pacific Ring of Fire forms a conservative plate margin where the North American and Pacific Plates slide past each other(1). This movement is not smooth. Plates get stuck, pressure builds and is released as an earthquake(1).
2. Along the east coast of Asia, the Pacific Plate subducts beneath the Eurasian Plate(1). Friction between the two plates causes a build-up of pressure (1). The plates are continually being driven along by convection currents in the molten magma of the mantle, so eventually the frictional resistance is overcome and the sudden slipping of the plates is felt as an earthquake (1).
Earthquakes also occur along the Mid-Atlantic Ridge at the boundary between the North American Plate and the Eurasian Plate - This is a constructive plate margin(1). Convection currents are forcing the two plates apart. As magma rises it causes earthquakes(1).
Earthquakes occur on plate margins(1) in long narrow belts (1). Earthquakes occur along conservative margins where plates slide past each other e.g. San Andreas Fault (1). They also occur along destructive plate margins where oceanic plates subduct (1) continental plates e.g. around the Pacific Ring of Fire(1). Finally, earthquakes occur along constructive margins where magma rises and causes volcanic eruptions (e.g. Mid Atlantic Ridge)(1).
Earthquakes happen on the edge of plates (1). When plates slide past each other they get stuck. When they slip they cause earthquakes(1). Also, plates go under each other. This causes earthquakes.(1)
2. With reference to a named earthquake, describe the immediate hazards and the longer-term consequences for people and the environment. (8 marks)
At 3.02 am on 17th August 1999, an earthquake lasting 45 seconds and measuring 7.2 on the Richter Scale struck north-west Turkey. The immediate hazards were the collapse of buildings (1) and damage to power lines and pipes causing fires (1). People were trapped in houses as they slept and many were killed by falling masonry (1). In all, 17,000 people died and over 27,000 were injured. Tidal waves flooded farmland on the coast causing damage to crops (1). Fire at an oil refinery caused air pollution (1). The longer-term consequences were that 200,000 people were made homeless (1) and had to live in tents for many weeks with no running water or proper sanitation (1). People suffered from diarrhoea due to lack of clean water (1) and untreated sewage contaminated rivers killing fish (1).