NOAA TSUNAMI BUOY FEELS' ALASKA EARTHQUAKE
January 11, 2001 A magnitude 6.9 earthquake occurred at 11:03 a.m. EST Wednesday morning about 70 miles southwest of Kodiak, Alaska. NOAA's tsunami warning centers located the position of the earthquake, assessed its magnitude, and issued an information bulletin minutes later.
A few minutes after the warning was issued, a NOAA tsunami detection buoy picked up the earthquake waves that displaced the seafloor instrument that triggered the buoy to start transmitting 1 minute data. At that time these data were plotted on the centers' Web site.
"The detection buoy, located off the Alaskan coast, performed as designed in detecting an abrupt change in sea level and sending data via the NOAA GOES satellite to the NOAA tsunami warning centers and to its Pacific Marine Environmental Laboratory in Seattle where these data were plotted on a Web site. Anyone on the Web could view these data 10 minutes after the earthquake ruptured," said Eddie N. Bernard, director of NOAA's laboratory in Seattle, Wash. "More important, the data showed that no
tsunami was generated either by the earthquake or an underwater landslide induced by the earthquake."
Charles McCreery, geophysicist in charge of the National Weather Service's Pacific Tsunami Warning Center, one of two such centersthe other is in Alaskasaid, "While the earthquake was too small to automatically trigger a tsunami warning, the Pacific Tsunami Warning Center closely monitored the Kodiak buoy data to quickly confirm that potentially destructive tsunami waves were not propagating towards Hawaii or the rest of the Pacific."
The buoy is part of the Deep-ocean Assessment and Reporting of Tsunamis or DART project, which offers early detection of tsunamis and for assessing and forecasting the
threat to coastal communities. DART also reduces false alarms that undermine the credibility of the warning system and are extremely expensive; 75% of all warnings issued since 1948 have been false, and the evacuation of Honolulu in 1986 cost more than $30 million.
The Pacific Marine Environmental Laboratory has developed a system that acoustically transmits data from a Bottom Pressure Recorder (BPR) to a surface buoy, which then sends the data to shore-based receivers through a satellite communications link. The BPR research experience over the last 10 years indicates that these real-time systems are capable of detecting deep ocean tsunamis with amplitudes as small as 1 cm. A
prototype system was fabricated, tested, and successfully deployed for two months off the Washington-Oregon coast in 1995.
There are now four buoys located from the Aleutian Islands to the Washington-Oregon coast.
A tsunami is a series of ocean waves generated by any rapid large-scale disturbance of the sea water. Most tsunamis are generated by earthquakes, but they may also be caused by volcanic eruptions, landslides, undersea landslides, or meteor impacts.
Tsunami is a Japanese word, represented by two characters: tsu meaning "harbor" and nami meaning "wave." Tsunamis rank high on the list of natural disasters. Since 1850 alone, tsunamis have been responsible for the loss of more than 120,000 lives and billions of dollars of damage to coastal structures and habitats.
Tsunami waves radiate outward in all directions from the disturbance, and can propagate across entire ocean basins. For example, an earthquake in Chile caused a tsunami across the Pacific in Japan. Tsunami waves are distinguished from ordinary surf waves by their great length, often exceeding 100 miles in the deep ocean, and by the long amount of time between successive peaksfive minutes to an hour. The speed at which tsunamis travel depends on the ocean depth. A tsunami can exceed 500 mph in the deep ocean but slows to 20 or 30 mph in the shallow water near land. In less than 24 hours, a tsunami can cross the entire Pacific Ocean.
In the deep ocean, a tsunami is barely noticeable and will only cause a small and slow rising and falling of the sea surface as it passes. Only as it approaches land does a tsunami become a hazard. As the tsunami approaches land and shallow water, the waves slow down and become compressed, causing them to grow in height. In the best of cases, the tsunami comes onshore like a quickly rising tide and causes a gentle flooding of low-lying coastal areas.
Relevant Web Sites
NOAA's Tsunami Research Program
NOAA's Pacific Tsunami Warning Center
NOAA's National Tsunami Hazard Mitigation Program
NOAA's Tsunami Database
NOAA's Tsunami Data from NOAA's National Geophysical Data Center
Tsunami Damage Photos
NOAA's National Weather Service Forecast Office, Honolulu, Hawaii
NOAA Weather Radio
Jana Goldman, NOAA Research, (301) 713-2483 ext. 181