Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Poster

S (Solid Earth Sciences) » S-CG Complex & General

[S-CG67] Ocean area observation to detect crustal activity under the seafloor: Present and future

Thu. May 24, 2018 10:45 AM - 12:15 PM Poster Hall (International Exhibition Hall7, Makuhari Messe)

convener:Kazuro Hirahara(Department of Geophysics, Earth and Planetary Sciences, Graduate School of Sciences, Kyoto University), Ryota Hino(Graduate School of Science, Tohoku University), Takane Hori(独立行政法人海洋研究開発機構・地震津波海域観測研究開発センター)

[SCG67-P10] Mobile pressure calibrator for ocean bottom pressure gauge of the DONET
Part 2: Development of level adjustment Unit

*Shuhei Nishida1, Yuya Machida1, Eiichiro Araki1 (1.Japan Agency for Marine-Earth Science and Technology)

Keywords:ocean bottom pressure gauge, crustal deformation, DONET

In Nankai Trough area, to prepare for the occurrence of large earthquake, DONET (Dense Ocean-floor Network system for Earthquakes and Tsunamis) was developed and installed, which is a submarine cabled real-time observation network for earthquakes and tsunamis monitoring for hypo-central region Tonankai and Nankai earthquake at southwestern Japan.
The ocean bottom pressure measurements in DONET have been expected to detect long-term ocean bottom crustal deformations. However, the pressure values at ocean bottom contains the drifts of the pressure gauges in addition to the pressure changes associated with crustal deformations on the sea bottom. The sensors of DONET have been installed and operated on the seafloor for about eight years in the longest. It is reported that each pressure gauge has different drift characteristics and that it has a displacement of 10 hPa/year at maximum depend on long-term observation. In order to remove the instrumental drift of each pressure gauge which deployed wide area, we have been developing the in-situ calibration technology for ocean bottom pressure gauges of DONET. This calibration system is put near the pressure sensing system of DONET using a ROV. And then, it measure the desired pressure at the pressure gauge level. In order to measure precise pressure, it is necessary to adjust the difference of level between the mobile pressure calibrator and the target pressure sensing system within 1 mm from the position up to 5 m away. The developed mobile pressure calibrator consists of the pressure measurement unit and the level adjust unit. The level adjust unit adjusts the level of the pressure measurement unit to the level of the pressure sensing system of DONET using four motors, inclinometer, camera, and line laser. The adjust range of level is 300 mm, accuracy is about 1 mm.
After adjusting the level, the value of reference pressure sensor is the calibration value of the target pressure sensing system in DONET. We have been carried out onshore tests continuously for the offshore test at early 2018. The proposed calibration method and results on/offshore test will be reported.