Japan Geoscience Union Meeting 2023

Presentation information

[J] Online Poster

S (Solid Earth Sciences ) » S-SS Seismology

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

Tue. May 23, 2023 10:45 AM - 12:15 PM Online Poster Zoom Room (14) (Online Poster)

convener:Masanao Shinohara(Earthquake Research Institute, University of Tokyo), Ryota Hino(Graduate School of Science, Tohoku University), Shuichi Kodaira(Research Institute of Marine Geodynamics, Japan Agency for Marine-Earth Science and Technology), Shin Aoi(National Research Institute for Earth Science and Disaster Resilience)

On-site poster schedule(2023/5/22 17:15-18:45)

10:45 AM - 12:15 PM

[SSS12-P14] Seafloor crustal deformation off the east coast of the Izu-Oshima island caused by the volcanic activities using the Long-term ocean bottom pressure recorder (LT-OBPR)

*Yuya Machida1, Shuhei Nishida1, Hiroyuki Matsumoto1, Eiichiro Araki1 (1.Japan Agency for Marine-Earth Science and Technology)

Keywords:Izu-Oshima island, Crustal deformation, volcanic activity, Calibration of the pressure gauge, Mobile Pressure Calibrator

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.