With the technology just described, it is possible to detect earthquakes in the early stages of fault rupture, rapidly predict the intensity of the future ground motions, and warn people before they experience the intense shaking that that might be damaging. Earthquake early warning systems detect strong shaking near an earthquake’s epicenter and transmit alerts ahead of the seismic waves. Potential warning times depend primarily on the distance between the user and the earthquake epicenter. There is a “blind zone” near an earthquake epicenter where early warning is not feasible, but at more distant sites, warnings can be issued from a few seconds up to about one minute prior to strong ground shaking.
Earthquake early warning systems have already been deployed in at least 5 countries—Japan, Romania, Taiwan, and Turkey—and a prototype system is being developed in the United States. Japan is the only country with a nationwide system that provides public alerts. A national seismic network of nearly 1000 seismographs is used to detect earthquakes and issue warnings, which are transmitted via the Internet, satellite, cell phones, as well as automated control systems that do such things as stop trains and place sensitive equipment in a safe mode. Earthquake early warning systems are being developed in the states of California and Washington, but their full deployment has not yet been funded by the U.S. Congress or state legislatures.
The great tsunamis generated by the Sumatra earthquake of 2004 and the Tohoku earthquake of 2011 illustrate the issues associated with tsunami warning. Because tsunami waves travel 10 times more slowly than seismic waves, there is enough time after a large suboceanic quake occurs, sometimes many hours, to warn people on distant shorelines of an impending disaster. Warnings broadcast by the Pacific Tsunami Warning Center, based in Hawaii, after the Tohoku earthquake allowed islands such as Hawaii and the western coastlines of the Americas to be evacuated prior to the tsunami arrival (see Figure 13.22). Unfortunately, no such system had been installed in the Indian Ocean, so the 2004 tsunami struck with essentially no warning, killing tens of thousands.
The most difficult situations arise in areas located close to active offshore faults, where tsunamis arrive so quickly that there is no time for a warning. One such place is Papua New Guinea, where in 1998, a tsunami killed as many as 3000 people in coastal villages near the epicenter of the quake that caused it. Such communities could be protected by building barrier walls to block inundation by ocean water, but this type of construction is expensive and has been tried only in Japan with mixed results (Figure 13.31). In these places, the best warning system is a very simple one: if you feel a strong earthquake, move quickly away from the coastal lowlands to higher ground!
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Individuals living in seismically active areas need to prepare for earthquakes and know how to respond when one strikes. Here are seven steps to earthquake safety, recommended by the Southern California Earthquake Center, that you can use to protect yourself and your family.
Before an earthquake occurs:
During an earthquake:
After an earthquake:
For further information, see Putting Down Roots in Earthquake Country, Southern California Earthquake Center, available online at http://www.earthquakecountry.info/roots/index.php.
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