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Answers to Video Exercises
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Chapter 1
Chapter 2
Chapter 3
Chapter 4
Chapter 5
Chapter 6
Chapter 7
Chapter 8
Chapter 9
Chapter 10
Chapter 11
Chapter 12
Chapter 13
Chapter 14
Chapter 15
Chapter 16
Chapter 17
Chapter 18
Chapter 19
Chapter 8: Earthquakes and Earth’s Interior
Indian Ocean Earthquake and Tsunami
Critical Thinking Question 1:
If we consider the Indian Ocean earthquake as 9.1 on the Richter Magnitude Scale, how does
this event compare with the 1906 San Francisco earthquake (approximately Richter 8.1) and the
1989 San Francisco Loma Prieta earthquake (approximately Richter 7.1)?
Suggested Response: Direct comparisons between Richter magnitudes must consider that the
Richter Magnitude Scale is a logarithmic scale. Therefore, each increase in number value is
associated with a wave amplitude increase of 10. If students compare the 1906 San Francisco
earthquake with the 2004 Indian Ocean earthquake, they should realize that the 2004 Indian
Ocean earthquake had an amplitude ten times larger than the 1906 earthquake. Likewise, a
comparison of the Indian Ocean earthquake with the 1989 Loma Prieta earthquake reveals that
the Indian Ocean earthquake’s amplitude was 100 times greater (102 or 10 x 10 = 100) than the
1989 Loma Prieta earthquake. Given these earthquake amplitude differences, it is not
surprising that the Indian Ocean earthquake, and resultant tsunami, were so devastating to the
region.
Critical Thinking Question 2:
Why did the Indian Ocean earthquake produce a tsunami? Will all earthquakes result in a
tsunami?
Suggested Response: Earthquakes result from tectonic movements, or from magma
movement within a volcanic magma chamber. Not all earthquakes will have great potential for
tsunami production. The earthquake event must displace water for a tsunami to occur, and this
will happen if faulting occurs within, or immediately adjacent to, an ocean basin. Furthermore,
not all faults result in vertical movement. Whereas dip slip faults (normal faults, reverse faults)
result in vertical movement across the fault zone, strike-slip faults result in lateral movement.
Therefore, the most likely earthquakes to produce a tsunami would be those that result in
vertical movement (dip slip faults), located within or adjacent to an ocean basin. (The Indian
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Ocean earthquake resulted in upward movement of the Burma tectonic plate by 15 meters, or
50 feet.)
Tsunami Warning System in the Indian Ocean
Critical Thinking Question 1:
Will DART buoys be effective at warning villages in all situations? What would happen if a
tsunami was generated fairly closely to a beach?
Suggested Response: Although the DART system is a good tsunami detection and warning
system, it will not be effective in all situations. If an earthquake or slump triggers a tsunami
near a coastline, the inhabitants will have relatively little warning to move to higher ground.
This occurred in 1993 off the coast of Hokkaido, Japan. Less than five minutes passed between
the earthquake event and the tsunami reaching the shore.
Critical Thinking Question 2:
What would cause the higher pressure of a tsunami wave that is detected by a DART buoy?
Suggested Response: The pressure is recorded at the ocean floor. A tsunami wave would have
greater height than typical waves in the area. The higher the column of water, the greater the
pressure recorded by the detecting device. (This is also similar to increased air pressure at
coastal areas as opposed to mountainous elevations. The column of air at sea level is longer
than the column of air above the highest peaks of the Rocky Mountains. Therefore, there is
greater air pressure at the lower elevation.)
Tsunamis December 2004
Critical Thinking Question 1:
How does the Indonesia tsunami of December 2004 compare to other great tragedies for loss
of life? Consider September 11, 2001 (although this was not a natural disaster) as well as the
Sichuan China earthquake of 2008.
Suggested Response: It is difficult to comprehend the magnitude of the loss of life from the
Indonesian tsunami. More than 200,000 people lost their lives in this natural disaster. The
September 11, 2001 tragedy resulted in a loss of almost 3,000 individuals. Therefore, the
Indonesian tsunami claimed 67 times as many lives! The Sichuan earthquake claimed almost
70,000 lives, but this natural disaster pales in comparison to the 2004 tsunami.
Critical Thinking Question 2:
Why can the tsunami waters travel so far on land? What finally slows the waters?
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Suggested Response: The waves have an incredible amount of energy. As the waves approach
land, the wave height increases as the waves compress. Once the tsunami waves encounter
land, they lose energy as they spread over the land surface, because of friction. As a result, the
tsunami waves tend to cause the most damage nearest the shore where the waves initially
break.