World's best warning system went off early
Tokyo: Millions of Japanese learnt about Friday's massive earthquake about one minute before they could feel its violent shockwaves, thanks to an early-warning system renowned to be the world's best.
The sophisticated system is connected to network of about 1,000 seismometers around the country which detect and analyse primary waves of quakes and issue warnings if the tremors are predicted to be powerful.
Primary waves travel faster than secondary waves, which are much more destructive - meaning that alarms about quakes can arrive moments before the earth starts to shake, just enough time to take cover.
"The system functioned well because warnings were seen on television across the country," Hirohito Naito, a seismic specialist at the Japan Meteorological Agency, told AFP.
The warnings were also issued through radio, television and via satellite data transmission systems -- as well as on mobile phone and email services for special subscribers.
In Tokyo, an early warning was flashed by public broadcaster NHK and private networks with loud chimes, interrupting normal broadcasting.
The first big shock was felt about a minute later in the capital area, swaying high-rise buildings and sending millions fleeing outside.
The state-run agency fully implemented the system in late 2007 and had issued warnings 17 times up until Thursday.
Japan accounts for around 20 percent of the world's most powerful earthquakes as it sits on the Pacific "Ring of Fire".
Taiwan and Mexico are also known to have earthquake early-warning systems.
"Other countries, like Mexico, have put such systems to practical use," Naito said. "But the system operated by the Japan Meteorological Agency is the only one which covers the whole area of a country."
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