Foundation, Concrete and Earthquake Engineering

Tsunami Warning System

Predicting where a Tsunami may strike helps to save lives and properties only if coastal inhabitants recognize the threat and respond appropriately. So scientists are trying to develop accurate and effective Tsunami warning system for many years.

Different organization like FEMA, NOAA and USGS are trying to tackle the threat of both local and remote source Tsunamis. As tsunami cannot be restricted, they are trying to establish an appropriate and effective warning system. Some of these attempts are stated below:

a) Tsunami Inundation Maps

The threat to specific coastal areas can be assessed by means of tsunami inundation maps. It delineates areas susceptible to Tsunami flooding, Earthquake-shaking Intensity, Liquefaction and Landslides. These maps provide critical guidance to local emergency planners, charged with identifying evacuation routes.

Coastal tide gauges have modified specially to measure tsunamis and seismic network have upgraded to have more rapid and more complete reports on the nature of the earthquake. But, as the tidal gauges spot tsunamis close to shore, they cannot measure tsunami energy propagating toward a distant coastline. As a result, an unacceptable 75% false-alarm rate has observed. These incidents are expensive, undermine the credibility of the warning system, and place citizens at risk during the evacuation.
Deep-Ocean Assessment and Reporting of Tsunami (Dart) System

b) Deep-Ocean Assessment and Reporting of Tsunami (Dart) System

Seismometers staked out around the ocean can almost instantly pinpoint a quakes location. In the next moment, complex computer programs can predict how long a triggered tsunami would take to reach coastlines, even though there have no yet a evidence of wave exists. After some minutes, tide gauges scattered along coastline may detect tsunami. But the only way to be sure whether a dangerous wave is headed toward a distant coast is to place tsunami detectors in its path and track it across the open ocean. This tsunami detectors is the DART system.

Tsunami Warning System
The DART system depends on bottom pressure recorders. As the crest of a tsunami wave passes by, the bottom recorder detects the increased pressure from the additional volume of overlying water. Even from 6,000 meters depth, the sensitive instrument can detect a tsunami no higher than a single centimeter. Ship and storm waves are not detected, because their length is short and, as with currents, changes in pressure are not transmitted all the way to the ocean bottom. When the bottom recorders detect a tsunami, acoustic chirps will transmit the measurements to a car size buoy at the ocean surface, which will than relay the information to a ground station via satellite.

Tsunami Warning SystemMore buoys would reduce the possibility that tsunami waves might sneak between them. Combined with the buoy measurements, the simulations of tsunami in computer will provide more accurate predictions to guide officials who may have only a few minutes to decide whether to sound an alarm.

c) Zoological Hypothesis:

Some zoologists hypothesise that animals may have an ability to sense subsonic Rayleigh waves from an earthquake or a tsunami. Some animals seem to have the ability to detect natural phenomena and if correct, careful observation and monitoring could possibly provide advance warning of earthquakes, tsunami etc. However, the evidence is controversial and has not been proven scientifically. There are some unsubstantiated claims that animals before the Lisbon quake were restless and moved away from low lying areas to higher ground. Yet many other animals in the same areas drowned. The phenomenon was also noted by media sources in Sri Lanka in the 2004 Indian Ocean earthquake.

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