• 2011 Tohoku tsunami;
  • nearshore currents;
  • resonance oscillation;
  • tsunami measurements

[1] The 2011 Tohoku earthquake of Mw9.0 generated a massive tsunami that devastated communities along the northeastern Japan coasts and damaged coastal infrastructure across the Pacific. A nearshore observatory in Honolulu recorded clear signals of the surface elevation and flow velocity at 12 m water depth, where adjacent harbors and marinas experienced persistent hazardous surges. The measurements allow validation of numerical model results, which in turn reveal complex oscillation and flow patterns due to resonance over the insular shelf and reef system. The computed wave amplitude and flow speed increase from 0.4 m and 0.1 m/s at the 100-m depth contour to 1.6 m at the shore and 3.3 m/s near an entrance to Honolulu Harbor. Although resonance of the tsunami along the Hawaiian Islands produced the strongest surface signal at 42 min period, standing waves with periods 16 min or shorter, which are able to form nodes on the reefs, are the main driving force of the nearshore currents.