2010 Chile and 2011 Tohoku Tsunami Profiles Measured by GPS Buoys and Coastal Wave and Tide Gauges in a Nationwide Ocean Wave Information Network for Ports and Harbors

Abstract

This paper introduces the tide data acquisition and processing procedures in the Nationwide Ocean Wave Information Network for Ports and Harbors (NOWPHAS), especially those for global positioning system (GPS) buoys that measure water surface elevations using real-time kinematic GPS technology at water depths of 100–400 m and 10–20 km from the coastline. It then describes specific features of the 2010 Chile tsunami and the 2011 Tohoku tsunami, including foreshock and main shock profiles, which were measured along the Japanese coast by the NOWPHAS equipment. In the main shock of the 2011 Tohoku tsunami, the GPS buoy at a water depth of 204 m off Kamaishi Bay showed that the first wave crest consisted of primary slow and subsequent quick rises, and exceeded 6 m approximately 30 min after the earthquake occurrence. Some geometrically adjacent sets of GPS buoys, coastal wave gauges, and coastal tide gauges revealed the tsunami propagation and amplification near the coast.