Long-term features of quartz pressure gauges inferred from experimental and in-situ observations

DONET, i.e., the dense ocean-floor network system for earthquakes and tsunamis has started its operation in the Nankai Trough, SW Japan in the early of 2010, and followed by the extension to the westward region as DONET2 in near future. DONET observatory is composed of various sensors such as broadband seismometer, seismic accelerometer, tsunami meter, etc. The present study focuses on quartz pressure gauges being used as tsunami meters measuring water pressure change. In the present study, long-term pressure gauges´ characteristics have been evaluated by using the JAMSTEC´s high accuracy pressure standard before deploying into the deep-sea. The high accuracy pressure standard is mainly customized by a piston gauge, a pressure generator/controller, a reference pressure monitor, and a thermal controlled large capacity chamber, which virtually reproduces the deep-sea environment. 20 MPa hydraulic pressure was applied to the pressure gauges under the constant temperature of 2°C, which is equivalent to the ocean-bottom of 2,000 meters depth for the duration of approximately one month. As a result, sensors´ drift varies among pressure gauges, however, which implies that the gradual drift possibly occurs a few centimeters per month in maximum. We also discuss the sensors´ drift after deploying the deep-sea by analyzing the long-term in-situ observations, which shows that it continues at a rate of a few to ten centimeters per year in the early stage, then it tends to be reduced gradually.