At times during the last week and a half, news about Japan’s nuclear reactor crisis has nearly overshadowed the original events that started it all: the March 11 earthquake and tsunami. But these have nevertheless drawn attention to a system that has quietly been deployed and expanded over the last six years. DART (Deep-ocean Assessment and Reporting of Tsunami), developed over decades and funded with greater urgency after the Asian tsunami in 2004, provides real-time detection of a tsunami in the making.
DART consists of pressure sensors on the sea floor and on moored buoys. Seismic data are transmitted from the bottom sensors to the buoys and in turn to satellites, which relay the information to ground stations. With this information, the coastal areas likely to experience a tsunami—as well as the probable height of the waves—can be calculated and more accurate warnings issued. (This is a more efficient method, certainly, than the way I learned California was at risk that Friday morning: a phone call shortly after 4 a.m. from a well-intentioned relative in the Midwest, shouting “Wake up! It’s headed right for you!”)
At the time of the 2004 Sumatra-Andaman earthquake in the Indian Ocean, which caused the devastating Asian tsunami, there were only a handful of tsunami-detection buoys in place. Today there are 39, mostly in the Pacific Ocean, the result of collaboration among 26 countries around the earthquake-prone Pacific Rim. Because of the system, on March 11 NOAA was able to warn officials on the West Coast of the US, just 12 minutes after the earthquake occurred off the coast of Japan, that a tsunami was on the way.
This article from the San Francisco Chronicle has more information on the development of the tsunami warning system