The Earthquake Early Warning System worked

It was a scary morning.
A strong earthquake with a magnitude of 6.5 hit Shizuoka Prefecture, south west of Tokyo, at 5:07 a.m. on August 11 (Japan Time). So far one was killed and more than 100 were injured mainly in Shizuoka Prefecture. I’m living in Yokohama, Kanagawa Prefecture, which is next to Shizuoka.
Just before the time 5:07am, to be exact, 15 seconds before I felt the earth quake, I had been awakened by my phone. My phone was beeping and showed early earth quake warning, “Now you are going to be hit by earthquake soon.” That was the time at which I felt a strong fear for an unknown upcoming event. Could you imagine the situation in which you were sentenced to have a big earthquake hit 10 or 20 second beforehand? I experienced such a terrible but valuable occasion.

Then, let me explain how I came to know the event.
The prediction is owed to the Earthquake Early Warning system which provides advance announcement of the estimated seismic intensities and expected arrival time of principal motion. These estimations are based on prompt analysis of the focus and magnitude of the earthquake using wave form data observed by seismographs near the epicenter.
Japan Meteorological Agency (JMA) developed the core system in 20005 and deployed it in 2007 for a general use with communication systems. The core system is connected to not only broadcasters but also cellular phone companies. (see the above picture: source http://www.jma.go.jp/jma/en/Activities/eew1.html).

My colleagues developed well-integrated warning system called “Area Mail.” The emergency information “Area Mail” is a message based on the earthquake early warning distributed by the JMA via a local information distribution system developed by NTT DoCoMo. The distribution architecture is depicted in the next figure.
The location of the epicenter and the magnitude of an earthquake are immediately detected at observation points near the earthquake epicenter, and estimated from the difference in arrival times of the Primary (P) wave (about 7 km/s) which is produced by the initial tremor of the earthquake, and the Secondary (S) wave (about 4 km/s) which is produced by the principal motion. A prediction of the magnitude and arrival time of the earthquake can then be sent out as a warning. Emergency information “Area Mail” converts the earthquake early warning distributed by the JMA in an emergency information “Area Mail” message and broadcasts the message to mobile terminal users who are in the affected region.
For further information on the warning system see

At this time, the epicenter was located almost 200km south west of Yokohama, and the distance gave me 15-second long chance to worry about my next move.
Fortunately, I was not injured and my home was not damaged either. The technology is so advanced and told me a near future. Thanks God, It’s Free.