Quake Warning System Alerted Tokyo

[WestVirginiaRebel]

Wall Street Journal:

TOKYO—Some people in Tokyo were warned that a major earthquake was about to hit before they felt a tremor.

As an 8.9-magnitude earthquake struck Japan's northeastern coast Friday, the world's first early warning system—developed by the country's meteorological agency—detected the quake's shockwave near the seismic center and sent off the warning message, which appeared on national television and radio as well as mobile phone screens.

In Tokyo, because of its distance from northern Japan, the warning message reached people before the quake actually jolted the capital.

When an earthquake occurs, seismometers near its source detect the first shockwave, which is usually mild and harmless. This wave is followed by another wave that travels more slowly and is much stronger and potentially destructive.

The agency's computer system analyzes the first, faster-traveling wave and quickly estimates how powerful the second wave will be; if it is likely to be very powerful, the system immediately issues a warning message.

The message comes on TV and radio, and many Japanese cellphones can receive and display the message. Some power and gas facilities as well as railway and industrial systems automatically halt their operations the moment they receive the warning message, the spokesman said.

In places relatively far from the seismic center, people can receive the warning up to half a minute or so before the quake reaches those areas.

Japan is the only country that has such an early warning system, according to the meteorological agency. The agency developed the system with help from scientists and launched it in December 2007.
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How Japan knew when the "big one" was going to hit.