The tidal anomaly increased relatively slowly and quickly in the initial and subsequent part, respectively, of the first crest and consequently exceeded 6 m at the GPS buoy off Kamaishi Port. The tsunami was observed even in semi-closed bays on the East China Sea coast of the Kyushu Island.
Since 1970, the Ports and Harbours Bureau, Ministry of Land, Infrastructure, Transport and Tourism, Japan, and its associated organizations, including the Port and Airport Research Institute (hereinafter, PARI), have been conducting wave and tide observations around Japan, central data processing, and data dissemination, through the Nationwide Ocean Wave Information Network for Ports and Harbours, NOWPHAS (Nagai et al., 2008). The data accumulated through NOWPHAS include not only high-wave events, but also the tsunami triggered by the 1983 Nihonkai-Chubu Earthquake (Tanimoto et al., 1983), the 1993 Hokkaido-Nansei-oki Earthquake (Takayama et al., 1994), the 2010 Central Chile Earthquake (Kawai et al., 2011), and the 2011 off the Pacific coast of Tohoku Earthquake. Fig. 1 shows the three categories of equipment in NOWPHAS (Kawai et al., 2011). These are as follows:
GPS buoys (hereinafter, GB) that are moored at a spot of 100–400 m in water depth and 10–20 km off the coast and measure the water level every second using real-time kinematic GPS technology;
seabed wave gauges (WG) that measure the water level using the water pressure and ultrasonic waves every 0.5 s at a water depth of 20–60 m and are normally within a few kilometers of the shore; and
coastal tide gauges (TG) that measure the water level using a float on the water surface in a tide well on a seawall or a quay. This paper, therefore, describes the summary of the tsunami profiles acquired by the NOWPHAS equipment.
