Japan launched this week an automated system that intends to provide several seconds warning before shaking occurs after a major earthquake.
The system, which has been tested for more than a year, went into operation Monday morning at 9a.m. local time and is operated by the Japan Meteorological Agency (JMA). It links together about 1,000 seismographs throughout Japan with a fast network and computing to calculate the location and strength of an earthquake within a few seconds of it occurring.
The seismographs measure the weak but fast moving primary waves from an earthquake. These are followed by secondary waves, which move at about half the speed but which are much more destructive. The system attempts to beat the arrival of the secondary waves and provide a warning that strong shaking is about to occur.
How much warning people have will depend on how far they are from the earthquake.
Meisei Electric, a manufacturer of earthquake sensors, estimates that residents in Tokyo would have about 40 seconds warning if a long-expected earthquake occurs in the Tokai region, about 100 kilometers from Tokyo. In Shizuoka, the city nearest to the predicted epicenter, about 10 seconds warning would be given.
The Tokai quake is long overdue and is expected to kill up to 10,000 people and injure tens of thousands, according to government estimates.
From Monday the warnings will automatically flash across Japan's major TV channels and other companies are selling commercial systems that can do things like stop heavy factory machinery, halt trains, take elevators to the nearest floor and cut gas supplies.
Japan is one of the most seismically active nations on earth with about 100,000 earthquakes occurring in and around the country each year.
In 1923 Tokyo was largely destroyed and up to 142,000 people were killed by a quake that was estimated at between magnitude 7.9 and 8.4. More recently a magnitude 7.3 quake caused widespread destruction in the western Japanese city of Kobe and killed 6,434 people. Earlier this year a strong quake in Niigata struck about 19 kilometers from the Kashiwazaki-Kariwa nuclear plant, which is the world's largest nuclear plant by capacity, but no serious damage was caused at the plant.