27 August 2008 Lecture 8 Outline – Earthquakes/Tsunamis

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MAR110 LECTURE #8 Earthquakes and Tsunamis

Figure 8.2 Underwater Faulting & Sea Surface Distortion The underwater faulting illustrated above causes vertical displacement of the whole column of water above it –converting the kinetic energy of the faulting process - initially into the potential energy of a solitary wave. The energy in the solitary wave radiates outward from the generation site forming a circular wave front (?)

Figure 8.1 Tsunami Generation Mechanisms The two main causes of tsunamis are underwater earthquakes/faulting (left) and landslides (right). Both have the capacity to displace the large volume of water necessary to generate a tsunami. (NG)

27 August 2008 Lecture 8 Outline – Earthquakes/Tsunamis

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Figure 8.3 The 26 December 2004 Sumatra Tsunami The circular wave front of the Sumatra tsunami propagates throughout the Indian Ocean – striking various coastal regions hours after its generation. The differing wave heights at the different locations often reflect different wave shoaling conditions. (NG Apr05)

Figure 8.4 Tsunami Evolution Tsunami waves are barely perceptible, as they propagate in the open ocean because the sea surface slopes are so small. However as the water shoals the wave fronts steepen considerably.

27 August 2008 Lecture 8 Outline – Earthquakes/Tsunamis

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Figure 8.5 Sumatra Tsunami Evolution: First 30 Minutes The progression of the 2004 Sumatran tsunami showing the initial displacement (exaggerated) due to the undersea faulting; the wave front propagates at the speed of a jet airliner toward the nearest coast –Banda Aech, Sumatra. (NG )

Figure 8.6 Tsunami Shoaling The height of a tsunami grows dramatically as it comes a shore. Usually the water at the shore first recedes to feed the growth of the offshore tsunami wave.

27 August 2008 Lecture 8 Outline – Earthquakes/Tsunamis

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Figure 8.7 Tsunami Leading Trough Landfall - Chile 1868 (above). Ships are left “high and dry” during the minutes preceding the landfall of the Chilean tsunami of 1868. Minutes later the ships were being tossed around by a chaotic ocean. (below) Note the comparison of a 60ft (20m) wave and a 6-story high ship.

27 August 2008 Lecture 8 Outline – Earthquakes/Tsunamis

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Figure 8.9 Tsunami Coastal Flooding This sequence of photos shows a relatively small tsunami hitting a Hawaiian beach. (NH)

Figure 8.8 Tsunami Cresting The wave crests with heights ranging from a few 10s to 100s of feet (or 5 to 50 meters). The wave then breaks - followed by the inundation of the turbulent water comes ashore. Depending upon the slope of the coastal region, the tsunami wave can flood the coast up to miles inland. (ItO)

27 August 2008 Lecture 8 Outline – Earthquakes/Tsunamis

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Figure 8.11 Satellite Pictures Record Sumatra Tsunami Impact Banda Aceh, Indonesia both before (left) and after (right) the 12/26/2004 tsunami. Note the destruction of fields and vegetation as well as the flooding. (NG)

Figure 8.10 Sumatra Tsunami Landfall The 12/26/2004 tsunami as it makes landfall on a stretch of coastline. (NG)

27 August 2008 Lecture 8 Outline – Earthquakes/Tsunamis

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Figure 8.13 Tsunami Warning System The information from an array of buoys and gauges around the Pacific is interpreted at the Tsunami Warning Center in Hawaii to generate warnings about when a particular tsunami will impact the different locations in the Pacific. These warnings enable people to evacuate to safer locations. Prior to the December 2004 tsunami, the Indian Ocean did not have a similar warning system. One is being built now (NH)

Figure 8.12 Chilian Earthquake/Tsunami 1960 In 1960 the largest recorded earthquake (9.5 magnitude) off the coast of Chile triggered a large tsunami that spread across the Pacific Ocean – as mapped above. Many people in Hawaii, when warned of the incoming wave, went down to the beach to watch. The large amount of damage and death that ensued showed the need for education about the dangers of tsunamis and how to properly respond to them. (NH)