Journalism and the Tsunami
For the Pacific Northwest, a region with a geological profile not unlike that of the Sumatra region, the threat of an earthquake and tsunami on a scale similar to that seen in Southeast Asia in December is real.
The nightmare scenario-a 9.0 earthquake off the coast, a tsunami rushing at hundreds of miles an hour toward ports and villages, a surge of brown water, in places as high as 80 feet, pushing inland-is likely inevitable, given enough time. But that is reason to prepare, not panic, says Robert Freitag, executive director of the Cascadia Regional Earthquake Workgroup (CREW).
Freitag joined Brian Atwater, of the U.S. Geological Survey, and Timothy Walsh, director of geological hazards for the Washington Department of Natural Resources, for a discussion about what such an event might mean to the Pacific Northwest and how journalists might better understand, report, and help in times of geological disasters.
Atwater sees press coverage of the tsunami as an important opportunity to help people understand science that might keep them safe in the future, and suggests reporters use events like the tsunami as "teachable moments" to inform the public.
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Even though they are often referred to by non-scientists as "tidal waves," tsunamis are rarely shaped like waves. The usual image of a wave is a curling break common to surf waves. Tsunamis, however, hit shore in a more compact, higher volume push much like that of a hurricane storm surge. "Surf waves are wind-generated waves that push along the surface," Walsh explained. But the push for a tsunami comes from a deformation of the sea floor in an earthquake, so the energy source comes from the bottom instead of the top. The difference fundamentally changes the structure of the wave.
A tsunami, which may be traveling in excess of 500 miles and hour, may only have the a height of several feet while at sea. When the deep-water wave reaches land, it decelerates and builds a push that grows in accordance to the energy of the displacement that fueled it. This push does not curl over like a surf wave. (Despite this, a surf wave is often used as the tsunami image, including on official west-coast tsunami warning signs.)
In surf waves, the distance between the high-water and low-water point in the wave is usually easily visible as wave after wave rolls into the beach. In tsunamis, the distance between the peak and trough, which may be tens of miles, generally makes it impossible to see the wave as we see surf waves.
This explains why a tsunami's potentially deadly surge is sometimes foretold by a rapid retreat of the water from the shore, as it was in much of Andaman Sea area.
"The retreat is when the trough of the wave arrives before the crest," said Atwater . The larger the retreat is, the larger the impending surge.
According to Walsh the surge experienced in parts of the Aceh region of Indonesia was likely greater than initially reported. Data suggests that, in some locations, the surge may have reached more than 80 feet.
The panel also described how certain land features could have focused the water volume in certain situations, or allowed for the waves to penetrate further onto costal plains. In some cases the wave penetrated several miles inland. The Aceh region saw water laden with debris spreading destruction and saltwater contamination five miles or more upstream.
Researchers are studying data from the Indian Ocean region in an effort to better understand the possible effects of local land features if a similar event occurs on the Cascadia Subduction Zone, where the Pacific, Juan De Fuca and North American Plates meet. Scientists have evidence that the subduction zone has spawned similar powerful earthquakes in the past. (A complete version CREW's recently released report based on a hypothetical earthquake similar in size to the Sumatra quake occurring in on the Cascadia subduction zone can be found at www.crew.org in PDF format.)
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Journalists can also help by informing the public about efforts to prepare for potential earthquakes and tsunamis. Walsh noted that the two tsunami-warning centers for the Pacific region sent out major earthquake alerts shortly after the December 26 Sumatran quake was detected. No foundation for a warning system was available in any of the stricken countries of Southeast Asia, a fact which greatly contributed to the loss life.
Freitag describes a warning system as having four components: science, intelligence, decision and procedure. In Freitag's model, science is the measurement of the event that has the potential to create a tsunami. Intelligence is the conversion of the data into information for the public sector to use. The decision is the critical point where local government decides whether or not to issue a warning. The procedure is the plan of action set off by the warning.
Although the panelists were clear that the Pacific Northwest's warning systems are superior to what is found in the Indian Ocean , they noted several possible weak spots. According to a pair of reports recently issued by CREW, the inventories of materials necessary for our day-to-day life are reliant on the rapid delivery of materials. Necessities like food water and medicine are kept in small inventories and replenished on a short-term regular basis. This means that if transportation is disrupted by a major earthquake, the inventory of goods at hand would run out quickly, and the ability to replenish them would be halted by damaged infrastructure.
Another gap might be found directly along Freitag's four-point chain; each government body, be it a town, city, county or state, has a separate decision making process. In the case of a coastal evacuation for a potential tsunami, the decision to evacuate for one town might be made by a single individual who understands the scientific intelligence. In the next town it could be made by someone who has little understanding. In the next it could require the consensus of a town or county council, a time consuming situation when time is essential.
To remedy possible delays in decision and communication, the entire panel stressed the importance of individual planning and awareness of tsunami indicators. "Feeling a strong earthquake should be a first warning to evacuate," said Brian Atwater. He encouraged people not to wait for official confirmation of an evacuation. The panelists acknowledged that false alarms would likely occur. But they urged people to understand the importance of continued vigilance in the face of the uncertain prediction process.