Outline of the 2011 off the Pacific coast of Tohoku Earthquake (Mw 9.0)—Tsunami warnings/advisories and observations—

The Japan Meteorological Agency (JMA) is the sole authority to issue domestic tsunami warnings/advisories to the public in Japan. JMA issues the tsunami warnings/advisories based on hypocentral parameters such as location, depth and magnitude, and the tsunami-simulation database system which stores more than one hundred thousand cases of previously-conducted tsunami-propagation simulation results. This system enables tsunami warnings/advisories to be issued within about three minutes after events. For the devastating tsunami generated by the 2011 off the Pacific coast of Tohoku Earthquake on March 11, 2011, this system successfully functioned and the first warning was issued at 14:49 (Japan Standard Time), which was about three minutes after the occurrence of the earthquake. JMA also monitors sea-level data observed with 172 tide gauges and 12 GPS buoys (there were 11 at the time of the earthquake, and this increased to 12 in May 2011), and they are used for changing grades and areas of tsunami warnings/advisories. This time JMA raised tsunami-warning grades and widened warning areas seven times, and downgraded or cancelled the warnings/advisories four times. Mainly based on tsunami observations, all tsunami warnings/advisories were cancelled at 17:58 on March 13. This was about 2 days and 3 hours after the tsunami warning was issued.