10:45 〜 12:15
[SSS12-P14] 長期海底設置用水圧計で捉える伊豆大島東方沖の地殻変動
キーワード：伊豆大島、地殻変動、火山活動、水圧計の校正、水圧校正装置
Izu-Oshima Island is one of the volcanoes with a well-established observation system array, and seismic and volcanic activity has been well studied including the 1968 eruption. In particular, since the GNSS network was constructed, a pressure source (magma chamber) located at a depth of about 4-5 km from the caldera has been repeatedly expanding and contracting in cycles of 2-3 years. In addition, a deep low-frequency earthquake has occurred 5 km southeast offshore of Izu-Oshima, at a depth of 30 km or more. Because an activation of the deep low-frequency earthquakes and an swelling of the volcano edifice are synchronized, a supply/accumulation process of magma extend deeply is suggested (Watanabe 2012). However, it is difficult to estimate the position and depth of the deep pressure source suggested at a depth of about 30 km, because the observation network for detecting the crustal deformation of the Izu-Oshima volcano is located within the island. Then we have started a long-term pressure measurement off the east coast of the Izu-Oshima island since the 2021 to understand long-term crustal deformation caused by the pressure source of not only shallow magma chambers at a depth of several kilometers but also deeper pressure sources. A long-term ocean bottom pressure recorder (LT-OBPR) was developed to understand the crustal deformation associated with the Izu-Oshima volcanic activity.
Since there is no realtime monitoring system (on-line) network observation network such as the earthquake and tsunami observation and monitoring system (DONET) installed in the Nankai trough, it was decided to be an off-line type. For this reason, LT-OBPR is a low-power-consumption model that enables continuous observation for five years. LT-OBPR contains a measurement logger and a battery inside a pressure-resistant container made of titanium alloy with a diameter of 650mm, and a pressure gauge (Paroscientific's 8B7000-2-005), an underwater detachable connector for collecting data, and a weight for adjusting buoyancy are attached to the outside. An internal clock is used as the reference frequency source for the pressure gauge, and the internal clock and atomic clock (CSAC SA.45s) are periodically compared and calibrated to guarantee the accuracy of the measured pressure.
Because long-term pressure measurements contain inherent instrument drift up to 10 hPa/year (equivalent to 10 cm/year) in addition to the seafloor displacements, a correction of the inherent drift component using an absolute calibration system with a resolution better than 1 hPa is necessary when measuring long-term precise pressure on the seafloor. Therefore, annual calibration of the LT-OBPR using the mobile pressure calibrator (MPC) developed by Machida et al. (2020) is planned. In the KS22-J05 cruise, we have downloaded a year's worth of pressure data since the deployment of the LT-OBPR and carried out a first in-situ calibration using the MPC. In order to estimate the drift rate of the pressure gauge, the calibration at least twice is necessary, and the next calibration of the LT-OBPR is scheduled for May, 2023. In this presentation, we introduce the pressure record for one year from the installation and future plans.
Since there is no realtime monitoring system (on-line) network observation network such as the earthquake and tsunami observation and monitoring system (DONET) installed in the Nankai trough, it was decided to be an off-line type. For this reason, LT-OBPR is a low-power-consumption model that enables continuous observation for five years. LT-OBPR contains a measurement logger and a battery inside a pressure-resistant container made of titanium alloy with a diameter of 650mm, and a pressure gauge (Paroscientific's 8B7000-2-005), an underwater detachable connector for collecting data, and a weight for adjusting buoyancy are attached to the outside. An internal clock is used as the reference frequency source for the pressure gauge, and the internal clock and atomic clock (CSAC SA.45s) are periodically compared and calibrated to guarantee the accuracy of the measured pressure.
Because long-term pressure measurements contain inherent instrument drift up to 10 hPa/year (equivalent to 10 cm/year) in addition to the seafloor displacements, a correction of the inherent drift component using an absolute calibration system with a resolution better than 1 hPa is necessary when measuring long-term precise pressure on the seafloor. Therefore, annual calibration of the LT-OBPR using the mobile pressure calibrator (MPC) developed by Machida et al. (2020) is planned. In the KS22-J05 cruise, we have downloaded a year's worth of pressure data since the deployment of the LT-OBPR and carried out a first in-situ calibration using the MPC. In order to estimate the drift rate of the pressure gauge, the calibration at least twice is necessary, and the next calibration of the LT-OBPR is scheduled for May, 2023. In this presentation, we introduce the pressure record for one year from the installation and future plans.