Ch. 4 Learning Objectives

Which fault type would not be able to generate a tsunami?

Strike Slip Fault - Offsets blocks of crust in a horizontal direction due to shearing stress

What is a runup map? How is it useful?

Shows level to which the water traveled inland. Create map to show the area likely to be inundated by a given height. Better prepared = more lives saved.

How do DART buoys detect tsunami waves?

Detects faster moving seismic waves Reports sea level information at one minute intervals.

What are the different ways in which a tsunami can be produced?

Earthquake (most common) Underwater landslide Volcanic eruptions Extraterrestrial objects (e.g., asteroid or comet) (very rare)

How do earthquakes generate tsunamis?

Earthquake causes displacement of the seafloor. The upward or downward movement of the seafloor displaces the entire mass of water from the sea bottom to the ocean surface.

Explain the process of tsunami formation and development.

Earthquake uplifts seafloor. Tsunami waves move rapidly and are spaced long distances apart. Closer to land, water depth decreases and velocity of wave decreases. As water slows down, the height of the waves increase. First wave can be high. Will appear as a fast rising increase in sea level. Runup occurs. Expect series of waves for many hours.

Discuss what nations, communities, and individuals can do to minimize the tsunami hazard.

Have detection and warning systems in place. Engineer buildings to minimize destruction Create runup maps Leave land gap between water and buildings. Plant trees to reduce velocity of incoming water. Complete probability analysis. Educate the public. Bring community to tsunami ready status.

Identify the actions you should take and not take if a tsunami warning is issued.

Leave beach & low lying areas. Exposing of sea floor - wave is on the way. Tsunami may be small at one location - don't assume it will be the same everywhere. Series of waves up to an hour apart - stay away until tsunami warning has passed.

Summarize the linkages between tsunamis and other natural hazards.

Linked to submarine and coastal earthquakes & landslides Island volcanic explosions Oceanic impacts of asteroids

What was the biggest factor that caused the Indian Ocean tsunami of 2004 to be a catastrophe rather than a disaster?

People did not know what a tsunami was which meant they did not know the warning signs.

Synthesize the effects of tsunamis and the hazards they pose to coastal regions.

Primary effects are related to the inundation of the water and resulting flooding and erosion. Hazards are bare-eroding ground and areas covered with debris. Secondary Effects occur in the hours, day and weeks following the event. Fires can start in urban areas from ruptured natural gas lines, water can become polluted, disease can spread, etc.

What are the warning signs that a tsunami may be coming?

Receding sea waters.

How are boats at sea affected by tsunamis?

They appear as normal waves.

How do tsunami waves change as they approach the coastline? Think in terms of wave amplitude and wavelength.

Water depth decreases, so velocity of tsunami also decreases. Decreased spacing between wave crests (or wavelengths). As water slows down and piles up, height of the waves increase.