Utilization of temperature and pressure simulator for ocean-bottom and bore-hole observatories for quantitative crustal deformation

Abstract:

JAMSTEC has developed temperature and pressure simulator for ocean-bottom and bore-hole observatories in 2010, which is mainly composed of temperature chamber and hydraulic pressure standard. We call this equipment “environment simulator”. Temperature chamber is capable to control its target temperature from -10 to 180 ℃, hence it is supposed for ocean-bottom to bore-hole environment. Pressure standard in which the dead weight is mounded on the piston-cylinder module produces the reference pressure up to 100 MPa (ca. 10,000 meters deep), which makes it possible to apply the constant pressure to the pressure sensors via the hydraulic pressure tube. Thus, our environment simulator can demonstrate ocean-bottom or bore-hole environment in the laboratory. The main purpose of the pressure simulator is to evaluate long-term pressure sensor’s stability, i.e., sensor’s drift by applying the constant pressure under the constant temperature. Here, we introduce two applications of our environment simulator.

The first application is to evaluate the initial behavior of pressure sensors to be used in the Dense Ocean-floor Network system for Earthquakes and Tsunamis (DONET) in the Nankai Trough, Japan. DONET pressure sensors have been deployed in order for detection of not only tsunami but also crustal deformation. We applied 20 MPa pressure under 2 ℃ temperature to the pressure sensors for one month before deploying into the deep-sea. As a result, the initial sensor drift of 5 hPa per month in maximum was measured. The second application is to provide the reference pressure to the mobile pressure sensor which is designed for the in-situ calibration for the pressure sensors being in operation. We have developed the in-situ pressure calibration tool equipped with the high precision pressure sensor. The concept is that we carry the reference pressure to the on-site to calibrate the pressure sensor. Before carrying it to the deep-sea, the reference pressure is given to the mobile pressure sensor by our environment simulator. Temperature dependencies have been also evaluated by changing the temperature under the constant pressure. Thus, our environment simulator has contributed to some applications in terms of pressure sensors for long-term monitoring of crustal deformation in the ocean.