2006 年 22 巻 p. 523-528
This paper introduces a newly developed real time tsunami detection system using offshore water surface elevation data obtained from GPS buoys or seabed installed acoustic/pressure wave gauges. In order to eliminate high frequency components caused by wind waves and swells, shape of the numerical low-pass-filter was determined with consideration of its real-time efficiency. To eliminate lower frequency phenomena caused by astronomical tides and other causes such as water temperature change, 6 days continuous passed data were found to be necessary to obtain harmonic constants of the 4 principal tide components and averaged sea level. Miss-fixed and data-loss phenomena, which may appear in the GPS buoy observation, were also considered to elaborate the automatic system.
Proposed system was checked with the actual offshore tsunami observation data caused by the 2004 Tokaido-off and 2005 Miyagi-off earthquake tsunami events, and the applicability was well confirmed with exception during a huge typhoon caused abnormal waves and sea-level events.