On the Accuracy of Quartz Pressure Sensor in the Seafloor Affected by Transport Condition

Improving the accuracy of pressure measurements on the seafloor can reveal small vertical crustal deformations, contributing to the knowledge of earthquake-generation processes. The pressure, temperature, and attitude dependencies of a high-accuracy quartz pressure sensor have been evaluated in a laboratory environment simulating an in situ seafloor measurement at 2000-m depth. This depth corresponds to that of a seismogenic zone in the Nankai Trough, Japan. To detect crustal deformations on a centimeter scale, pressure measurements with an accuracy of 1 hPa, corresponding to a depth change of 1 cm, are required. High-resolution pressure measurements-and thus evaluation of pressure sensor dependencies-are critical. Temperature dependencies were evaluated by placing a gauge incorporating the sensor in a temperature-controlled bath from 2 °C to 24 °C under a constant pressure of 20 MPa. Pressure dependence was evaluated by changing the applied pressure from 10 to 30 MPa at a constant temperature of 24 °C. Attitude dependence was evaluated by tilting the gauge from 0° to 14° under constant pressure and temperature conditions. These results were used to investigate the impact of gauge transportation from the laboratory to the seafloor. We calculated changes in each factor sufficient to cause a measurement bias of 1 hPa: 1) a sensor temperature change of 0.3 °C; 2) a pressure variation of ±3 MPa from 20 MPa; and 3) a tilt change of 2.3°. The temperature dependence has the greatest influence on the measurement accuracy, highlighting the particular importance of ambient temperature change throughout the measurement procedure.