The Reliability of Tsunami Detection Buoys
The ocean-based tsunami detection system, known as the deep-ocean assessment and reporting of tsunamis (DART), which today sent warnings to residents on the west coast of the United States and Hawaii (as well as more than 50 other countries) is an unreliable system, according to 2010 report. Of the 39 stations deployed in 2008 only an estimated 60 percent were operational by 2009 (click here to see current active and inactive stations). The report, issued by the National Research Council of the National Academy of Sciences, concluded that the buoy stations, despite their technological achievements, may not be a feasible long term solutions for providing improved early warning and real-time reporting of tsunamis.
“The technology is good, but it’s designed for distance events like today,” says Nathan Wood, a research geographer at the U.S. Geological Survey and a member of the committee that issued the report. The massive 8.9-magnitude earthquake hit off the coast of Japan, giving residents of the United States enough time to prepare or evacuate. Tsunamis are capable of hitting earthquake stricken areas 15-20 minutes after the earthquake itself. But it takes several minutes for researchers at tsunami warning centers to gather seismic data, run models, and issue warnings. Having already lost about seven minutes, for example, those close to the epicenter have little time to evacuate or mobilize before the tsunami strikes, says Wood. Information from the buoys is utilized, roughly, anywhere from 10-60 minutes after an earthquake to confirm a tsunami event and determine the size of the waves. “There is just not time for warnings when a local event occurs.”
The DART system was developed by the National Oceanic and Atmospheric Administration in 2001. It consists of a bottom pressure recorder anchored to the seafloor and a moored surface buoy. Data from the pressure recorder is transmitted to the buoy via an acoustic link, and the buoy sends the data to a satellite that communicates with a control station. Most of the buoys are located in the Pacific Ocean where a tsunami landfall is thought to be more likely. Other locations include the Atlantic Ocean and Carribean.
Wood says the main problem with the buoy stations is that they are hard and expensive to maintain, and because they are located in a rather harsh environment, they have a fairly high failure rate. One trip to fix a failed buoy could cost $25,000. Each station was designed to be operational for at least four years, but after just one year, 2006, nearly 20 percent of the buoys were inoperable. The NRS/NAS report stated that at some points in time 30 percent or more of the buoys have been inoperable.
Another issue is that there is no “failure analysis effort”, says Wood. When the systems go offline it’s difficult to figure out why. And if one station becomes inoperable there is just no coverage in that area.
The report recommends that NOAA conduct a cost-benefit study and develop alternative methods. Wood says that while the technology is valuable and can be effective, the financial constraints of maintaining the stations might make them an unsustainable long term solution. What could make them better, he suggests, is if the system could expand beyond just scientist getting information via instant or text messages to people that need it to save lives or take action. He adds that the buoy systems could be financially sustainable if they were used for more than just tsunami warnings.
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