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A well-developed public earthquake early warning (EEW) system has been operating in Japan since October 2007. At the time of the 2011 Tohoku-oki earthquake and tsunami (also known as 3.11), several million people near the epicenter received the EEW about 15 to 20 seconds before the most severe shaking occurred, and many more people in surrounding districts had greater lead time before less severe shaking started. Some 90% of these people were able to take advance actions to save their own lives and those of family members or to take other actions according to prior planning. Some actions were taken based on intuitive responses to the alerts. This high rate of effectiveness is assured to be the result of education regarding the EEW system, both in schools and in society at large. In spite of some shortcomings, the proven effectiveness of EEW has led Japan to strengthen the already extensive seismic- and tsunami-monitoring networks offshore, east of the Japan island arc at 150 sites, and to provide a special terminal for advanced uses of EEW in schools with more than 53,000 students. Efforts are also underway to improve analysis and dissemination schemes.

Simultaneous measurements of the sea surface displacement and the longitudinal component of the wind velocity at several levels are reported. They were obtained at the Marine Tower under various conditions, with the air and the waves moving either in the same or in opposite directions. The spectral analysis was made. The cross-correlation coefficient between the sea surface displacement and the wind velocity is large at the layer adjacent to the surface and decreases with increasing mean wind velocity and height. Below a certain level which is several times or several tens of times higher than the height of the critical level where the wind velocity component in the direction of wave propagation equals the wave velocity, the phase lag of the Fourier component of the wind velocity compared with the surface elevation component is about 160 to 190°. Above this layer the wave-induced wind component is very weak and the phase reversal takes place at the height where the mean wind velocity equals 1·2 to 1·5C, C being the phase velocity of wave. When the wind blows in the opposite direction from that of the wave propagation, the wind fluctuation is in phase with respect to the wave motion and the amplitude of wave-induced wind component is relatively large. Some discrepancies are shown between the observations and the predictions from the theory of inviscid fluids.