CORE UNIT: P
ATTERNS AND PROCESSES IN THE PHYSICAL ENVIRONMENT 2.4 The effects of earthquakes
Earthquakes are traumatic events for the people who experience them. The social and economic effects are devastating. It may take years to rebuild damaged buildings and some people never recover from the psychological distress. Whole economies suffer as industrial capability is reduced and generations of people disappear.
Immediate effects:
1. Death and destruction, tsunamis, gas explosions, fire, loss of fresh water supplies, homelessness.
2. Liquefaction occurs where settlements are built on deep, loosely-consolidated soils or reclaimed land rather than on solid bedrock. The ground turns to liquid due to intense shaking during an earthquake. Buildings sink into the ground, e.g. Mexico City, Los Angeles.
Tsunamis
A tsunami is a destructive wave of water. Most tsunamis are generated by earthquakes, but they may also be caused by volcanic eruptions, landslides, undersea slumps or meteor impacts. The most devastating tsunami ever recorded occurred on December 26, 2004, in the Indian Ocean after the Southeast Asian earthquake. Sometimes when an earthquake occurs under the sea, movement of the sea floor
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The huge mass of water surged to the surface where it spread outwards in waves.
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The Asian tsunami travelled at about 800 km/h.
causes ripples on the sea surface, much like carrying a bowl of water makes it slosh around. The ripples travel extremely fast (500–800 km/h). In the open ocean they are barely noticeable but when they reach shallow water these waves slow down and the water piles up to heights of over 30 m. If
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As a wave reaches shallow waters it slows down, shortens and rears itself up, concentrating its energy into a smaller but more destructive package.
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Tsunamis more often occur as rapidly rising tides. Tides may retreat before the first wave hits, as happened in parts of Asia.
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Advancing waters can rise 30 m and flood areas more than 2 km inland from shore before forming a dangerous receding current.
the seabed is not
Ruptured sea floor
Tsunami sensor placed in Indian Ocean in 2006
Dry reef
exposed as tide quickly went out
disturbed by an earth- quake, a tsunami will not occur. One of the first warnings
Riptide: Victims were flung into trees by the initial
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A section of Earth’s crust below the Indian Ocean forced under another section off Sumatra, rupturing a 950 km stretch of sea floor and displacing millions of tonnes of water.
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waves, then they clung to branches as water rushed back into the ocean
The sea floor was uplifted by 2-6 m exposing coral reefs in places.
of a tsunami can be a rapid withdrawal of water from the beach. The water goes out suddenly, and between 5 and 30 minutes later it surges back and washes over the land with incredible power.
24 Fig. 10 How the Indian Ocean tsunami was caused Longer-term effects:
1. Migration – thousands are displaced while damaged buildings are cleared and rebuilt.
2. Disease – water and sewerage pipes burst and take time to repair.
3. Economic slowdown – shops close, industry is destroyed and government spending is diverted from other projects.
Indian Plate Burma Plate
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