Characteristics of the 2011 Tohoku Tsunami Waveform Acquired Around Japan by Nowphas Equipment

The 2011 Tohoku Tsunami was observed around Japan by NOWPHAS equipment. These devices include GPS buoys which measure water surface levels by real-time kinematic GPS technology and which are moored at sites 10 km to 20 km offshore where water depths range from 100 m to 400 m, seabed wave gauges at depths between 20 m and 60 m, and coastal tide gauges. A GPS buoy moored offshore of Kamaishi Port recorded the first tsunami crest, which rose in two steps and exceeded 6 m approximately 30 min after the earthquake. Data from some sets comprising GPS buoys, nearby seabed wave gauges, and coastal tide gauges determined the extent of the tsunami propagation and amplification on the coast. Resonance caused by the tsunami continued a day or more after the initial tsunami arrival in some stations. A Doppler-type wave directional meter located in the Tokyo Bay entrance acquired data on the vertically uniform distribution of the tsunami current traveling in and out the bay. The tsunami was detected at almost all of the tide gauges around Japan, even in the semi-closed Ariake and Yatsushiro Bays located on the East China Sea coast of the Kyushu region.