[S-SS12] Frontiers of Marine Observation for Earthquake, Tsunami and Crustal Deformation

[SSS12-P04] Development of long-term drift elimination system of OBP for deep-sea observation by "A-0-A" approach and comparison with DONET in-situ calibration results based on Mobile Pressure Calibrator

*Yusaku Ohta¹, Ryota Hino¹, Makiko Sato¹, Syuichi Suzuki¹, Hideto Otsuka¹, Hiroaki Kajikawa², Yuya Machida³, Shuhei Nishida³, Eiichiro Araki³ (1.Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, 2.National Metrology Institute of Japan, AIST, 3.Research and Development Center for Earthquake and Tsunami Forecasting, JAMSTEC)

Ocean bottom pressure gauge (OBP) can continuously observe the vertical crustal deformation on the seafloor. The long-term sensor drift of pressure sensors equipped with OBPs has been a profound and long-standing problem for detecting slow crustal deformation. One of the approaches to reduce the long-term drift from OBP record is the so-called “A-0-A” method. The method uses atmospheric pressure in the housing as the reference pressure. Based on these backgrounds, we developed a prototype of OBP with the “A-0-A” function, which can be deployed to a deep (~ 6,500 m) sea environment. We adopted a standard 17-inch glass sphere as the pressure housing. In the system, a pressure sensor must be installed in the housing, and the water pressure must be applied through a penetrator hole of the glass sphere. A three-way ball-valve is placed in front of the sensor so that the applied pressure can switch between outside (water pressure) and inside (air pressure in the housing). A precise barometer is also installed to measure the internal pressure because the pressure data is used as references to know the drifting nature of the pressure sensor at its “zero-point”. To assess the ability of the developed system, we conducted 341 days sea-trial in the Nankai Trough. We installed the system on the seafloor of 1,800m depth with a free-fall and pop-up recovery system, where just nearby the 2C-10 DONET station. We successfully obtained both water pressure and internal pressure records measured by a single deep-sea water pressure sensor (Paroscientific, 410K-291). The obtained internal pressure showed a gradually increasing pressure trend, which agreed well with the long-term trend of the external water pressure record. The obtained internal pressure record was used to correct the external water pressure record. Fitting annual, semiannual, and linear trend functions to the corrected time series confirmed a pressure increase of several hPa/year. The presentation will provide a more quantitative evaluation of the drift removal capability of the A-0-A system by comparing it with the in-situ calibration of pressure gauges using Mobile Pressure Calibrator that JAMSTEC has been performing at DONET.