A magnitude 8.8 earthquake struck off the coast of Chile late yesterday evening (10:34 PT), killing scores of people in Chile and causing Hawaii to brace for its biggest tsunami since the Alaskan earthquake of 1964.
The tsunami alert went out hours before the first waves, traveling at the speed of a passenger jetliner, were expected to hit Hawaii at 11:19 this morning, local time (Video: Tsunami 101).
Tourists and coastal residents are expected to wake up to tsunami alarms and evacuation instructions several hours earlier, tsunami authorities told the Associated Press (tsunami safety tips).
The earthquake occurred along the junction of the Nazca and South American tectonic plates, which are colliding off the coast of Chile at a rate of 3 inches (80 millimeters) per year (map of Chile).
The coastline of Chile is one of the most active tectonic zones in the world, with 13 temblors of magnitude 7.0 or greater since 1973, the U.S. Geological Survey reports on its earthquake-monitoring Website.
In May, 1960, the same region produced the largest earthquake ever to be measured with modern instruments. That temblor had a magnitude of 9.5 and produced a tsunami that killed 61 people in Hawaii, Japan, and the Philippines.
The greatest safety concerns are in Hawaii, but nevertheless, a region from California to Alaska has been put under a tsunami advisory.
Advisories are the second stage of the National Oceanic and Atmospheric Administration's four-step tsunami warning scale. Rather than urging evacuations, as are being done in Hawaii, an advisory warns of the possibility of strong currents and advises residents to stay out of the water, NOAA's Website explains.
Other scientists, tracking Twitter uses of the word "earthquake" or its equivalent in other languages, have found that the earthquake was felt far enough to set people to tweeting about it to their friends as far away as the Atlantic Coast of Argentina.
"You start getting tweets seconds after an earthquake," says Paul Earle, a seismologist with the United States Geological Survey who uses the system to produce quick reports of earthquake damage. "The system continuously gathers all the tweets, and when there's an earthquake, it pulls out the tweets we think are associated," he says.
No such system yet exists, however, for tracking tsunami reports as waves cross the ocean.