FIELD INVESTIGATION OF LONG-TERM MOORING CHAIN SYSTEM DURABILITY OF THE GPS TSUNAMI-WAVE METER

Abstract

This paper aims for providing basic information of the mooring design of the GPS mounted Tsunami-Wave meter buoy, which successfully observed exact offshore tsunami profile of the 2011 off the Pacific coast of Tohoku Earthquake. Deep-sea sensors can detect tsunami profiles minutes before its arrival on the coast. That is very important to prevent and/or reduce tsunami disasters (Nagai, et.al., 2006). But as tsunamis are very rare events for human life scale, it is difficult for human societies to keep the offshore tsunami monitoring system in good condition for long years, if the system is applicable only for tsunami detection. Real-time offshore tsunami detection system should be well maintained only if the system provides us routine useful sea information like waves and swells. Routine multi-purpose usefulness of the observed data may make the system more cost effective than only be applicable for very rare and immediate tsunami monitoring (Nagai, et.al., 2007). Existing deep-sea seabed installed pressure gauge is applicable only to tsunami event, for deep-sea wave and swell actions do not reach the seabed. That is why offshore GPS buoy system is the only one technique that has succeeded to serve authorized real-time tsunami warning before its arrival to the coast line at the 2011 off the Pacific coast of Tohoku Earthquake tsunami event in Japan. In this paper, authors introduce observation data of proto-type GPS buoy's mooring chain at 3 years and 7 months after the installation in the severe sea condition, in order to provide information for practical design of future safer and more economical design of the mooring system.