Chapter 7: Tsunami
Are tsunami waves related to tides?
-No. Tsunamis are not associated with tides. Tsunamis are seismic sea waves produced by the sudden vertical displacement of ocean water. A tidal wave is caused by the atmosphere; pertaining to gravitational influences of the moon, sun, and planet.
What strategies are used to minimize tsunami hazards?
- Detection and warning: EQ detection GPS buoys are connected to seismic stations and receive data from the ocean floor bottom sensor . When theirs movement, sensor sends signal to buoy and satellite, and can hopefully give enough warning time. - Structural Control: Large buildings can be built to withstand tsunami. Sea walls can protect shorelines, but sea walls are also damaging to ecosystems on the coast though. Mangroves and trees help with coastal flooding, by soaking up some of the water. - Tsunami risk maps: Maps that show that tsunamis are most likely to occur in low lying areas, usually where ships come in since ships can easily dock in low areas. (EX: Marina del Rey and Long Beach Port). - Land use planning: Prevent new construction in areas that are prone to runup. - Probability analysis: Probability of tsunami occurring and the consequences it will endure. - Education and readiness: Educating the public on recognition, strategy, and preparation.
How do earthquakes cause tsunami?
- EQ can cause a tsunami by movement of the seafloor and by triggering a landslide. (can also occur without earthquake). Movement occurs when the seafloor sits on the block of earth's crust that shifts up or down during a quake. 1) EQ rupture in seafloor pushes water upwards starting the tsunami. 2) Tsunami moves rapidly in deep ocean reaching speeds greater than 500 km/hr. 3) As tsunami nears land it slows about about 45 km/hr but is squeezed upwards, increasing its height. 4) Tsunami heads inland destroying all in its path.
What are some causes of tsunami?
- Earthquakes (most common) - Volcanic Eruptions - Landslides - very rarely, a meteorite strike.
Tsunamis in open ocean...
- Fast - long wavelength. - small wave height.
What is the difference between a distance and local tsunami wave?
- Fault displacement lifts water above mean sea level, which creates potential energy that drives the horizontal propagation of the waves. The initial wave is split into: - Distant Tsunami: Travels out across the deep ocean at high speed. Distant tsunamis can travel thousands of kilometers across the ocean to strike remote shorelines with very little loss of energy. - Local Tsunami: Heads in the opposite direction toward the nearby land. A local tsunami can arrive quickly following an EQ, giving coastal residents little warning time. - When the initial tsunami wave split, each(distant and local) has a wave height about one-half of that of the original dome of water.
What problems do tsunami cause (in addition to coastal flooding)?
- Flooding. - Fires: caused by ruptured gas lines or from the ignition flammable chemicals that were released from damaged tanks. - Pollution: Tsunami causes ton of human and natural debris. - Disease: Spreads from contaminated drinking water and after flood their standing water; which brings/attracts mosquitoes. - Saltwater intrusion: Balance between groundwater and saltwater is delicate balance. If groundwater is sinking into continents and ocean water is sinking too and the sea level rises from storms, then saltwater infiltrates into aquifer. Once salt in groundwater, it's really hard to get rid of it.
Is southern California at risk of tsunami?
- Southern California is at a significant hazard to having a tsunami, but it is not the greatest hazard or lowest hazard, meaning it is intermediate. - The tsunami return period is every 500 to 2000 years. It is adjacent to active continental faulting with slow or disturbed plate boundary collision zones, or in regions at moderate distances from subduction zones capable of great EQs.
How do tsunami waves change as they approach shore?
- The waves are shorter on the bottom and taller on the top. - "Feel Bottom" occurs when wave energy drags across the bottom and slows the wave down and compresses wave, and past 1/7 becomes weak and falls over itself. - As it nears land, the water depth decreases, so the velocity of the tsunami also decreases. Near land, forward speed may be about 45 km per hour-too fast to ourtun, but not nearly as fast as waves in the open ocean. This decrease in velocity also decreases the spacing between wave crests, that is, the wavelength. As the water slows down and piles up, the height of the wave increases.
How do you calculate the velocity of a tsunami wave in open ocean water? *
Velocity in open ocean=v(depth x 10m/sec^2)
