How far do human responses to tectonic hazards reflect the frequency and magnitude of the events? (70)

Other possible questions

• Discuss the challenges posed for communities by different tectonic hazards. (70)

• Examine the impacts caused by tectonic activity and explore the reasons for these vary. (70)

• "The severity of a hazard is determined by the economic situation in which it occurs". How far do you agree?

Event profiles

• Not all tectonic hazards are the same• Event profiles are a common way of comparing

different hazards• In this example the 2004 Asian Tsunami and

ongoing eruption of Kilauea on Hawaii are compared

• Hazard profiles can be drawn for any event.

Tsunami• Tsunami are relatively rare events.

• They are generated by submarine earthquakes, volcanic collapse, and coastal landslides, which suddenly displace huge volumes of water

• The 1993 Okushiri tsunami (Japan), 2004 Asian Tsunami and 2009 Samoa events are useful case studies.

• Tsunami waves are radically different from normal wind generated ocean waves.

• When a tsunami hits a coastline, the effect is more like a devastating coastal flood than a single breaking waves

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Asian Tsunami• One of the most devastating natural disasters

of recent history.

• 11 different countries affected.• Millions of people displaced.• Over 250,000 fatalities.

• But what exactly caused this phenomenon?• What natural forces were at work?• Will it happen again?

6

Earthquakes and Tectonics• The three major tectonic plates in the

region, the Indian, Australian, and Eurasian Plates, as well as the Burma Microplate were involved in generating the immense earthquake, measuring 9.0 on the Richter Scale and generating 750 times more power than the earthquake that struck Bam exactly one year previously.

• It is known as a ‘megathrust’, a sudden juddering movement beneath the sea floor.

• A build up of pressure under the Indian Ocean caused the sea floor to lurch up over 15 metres towards Indonesia; the Indian plate and the Burma microplate had been sliding against each other for centuries, but not at all smoothly. After a long timespan of accumulating pressure, the Indian plate jarred, forcing the Burma microplate upwards.

• Tsunamis travel at low heights over deep ocean; high waves occur when shallow water is reached.

A small animation showing the epicentre of the earthquake, and

the resulting tsunamis.Extracted from

http://en.wikipedia.org/wiki/2004_Indian_Ocean_earthquake

Top Right: The Major Tectonic Plates of the

World

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Forces and Timespans• The force generated by the three

individual tectonic ‘slips’, which occurred almost simultaneously, caused the Indian plate to move forwards, or rupture, over 1,200 kilometres.

• This was a type of subduction earthquake, in that one plate slips under another.

• The total force was enough to jolt the entire planet; the Earth was thrown off its axis by a few centimetres, and a few seconds of time was lost.

• The earthquake followed two centuries of pressure accumulating between the Indian and Burma plates, wherein up to this point, only slid against each other at an average rate of 6 centimetres per year.

• Some islands were moved by 20 metres and Sumatra was shifted almost 35 metres.

Countries most affected by the earthquake and tsunamis.

Extracted from http://en.wikipedia.org/wiki/2004_Indian_Ocea

n_earthquake

Information from www.nature.com/news

8

Probability of Occurrence• The likelihood of this earthquake

occurring was not particularly low, as there had not been any major earth tremors in the area for almost two centuries.

• The last major earthquake was in 1833 along that subduction zone.

• Due to this major earthquake, another one occurring soon is unlikely, as too much pressure has been released, and there has not been enough time for more pressure to accumulate in the region.

• Earth tremors occur all the time, and even slight earth tremors are detected in the United Kingdom. The tsunamis could only be caused by an underwater, or marine earthquake; a land-based earthquake would generate different damaging effects, and more of the pressure would have been absorbed by the land. On the other hand, water is not the best barrier for dissipating wave energy, as one can see from the devastation caused by these tsunamis.

Image depicting the locations of the initial earthquake, and the

aftershock.Extracted from

http://en.wikipedia.org/wiki/2004_Indian_Ocean_earthquake

Additional information from www.nature.com/news

Tsunami websites

• http://news.bbc.co.uk/1/hi/in_depth/world/2004/asia_quake_disaster/default.stm

• www.geographyinthenews.rgs.org/news/article/default.aspx?id=326

• http://www.guardian.co.uk/tsunami/

• http://en.wikipedia.org/wiki/2004_Indian_Ocean_earthquake