Signal-to-noise ratio and the isolation of the 11 March 2011 Tohoku tsunami in deep-ocean tsunameter records

The United States National Oceanic and Atmospheric Administration tsunami forecasting capability under collaborative development between the National Weather Service, the Pacific Marine Environmental Laboratory, the National Geophysical Data Center, and the National Data Buoy Center depends on rapid isolation of a deep-ocean tsunami signal during tsunami propagation. Typical tsunami signal-to-noise ratios in the deep-ocean are such that de-tiding based on a combination of standard tidal harmonic predictions and carefully constructed filters are necessary to isolate the tsunami from records dominated by local tides and environmentally induced background noise. The unprecedented amplitudes measured at deep-ocean tsunameter sites offshore Japan during the propagation phase of the 11 March 2011 Tohoku tsunami provide an atypical scenario of high signal-to-noise ratios by which to evaluate the historic nature of this tsunami in terms of signal isolation for the forecasting of tsunami amplitude and inundation along Pacific Basin coastlines. Tsunami isolation for real-time forecasting during the more typical event scenarios of 27 February 2010 Chile and 29 September 2009 Samoa require specific techniques to minimize impact on the tsunami signal.