3:30 PM - 5:00 PM
[SVC35-P06] Development and implementation of a multi-channeled seismometer system with phase-shifted optical interferometry in a volcanic environment
Keywords:Seismic Observation, Optical Interferometry, Volcano Observation, Eruption, lightning
Seismic observations were conducted by installing surface sensors near volcanic craters and in boreholes at the foots of volcanoes. It is necessary to monitor volcanoes for stable operation of observation equipment over time as the equipment may fail because of lightning or high temperatures. In addition, when an electric wire from the ground sensor is connected to the recording equipment, the effect of the lightning surge is obvious in the seismic records. Lightning device failures and lightning-surge noise contamination are unavoidable as long as electric wires are used. Optical fibers have recently been used for seismic observations without these wires. One of the methods is distributed acoustic sensing (DAS), which observes ground motion using optical fibers. In contrast, an optical sensor system using phase-shift optical interferometry was developed as a method to observe ground motion using a sensor connected to an optical fiber as a signal communication route (Yoshida et al., 2016; Ooe et al., 2018). The DAS method measures the strain vibration in the optical cable direction, whereas the optical sensor system measures the three-component vibration of translational acceleration. In the optical sensor system, the change in the pendulum amplitude that captures the ground motion owing to seismic waves is detected by the sensor as the phase difference of the laser light. The phase difference is transmitted as an optical signal through the fiber and converted into acceleration by a signal processor.
In the Integrated Program for Next Generation Volcano Research and Human Resource Development, the B2-2 project—“Development of a multi-channeled seismometer system with phase-shifted optical interferometry for volcanological observations”—set out to develop an optical sensor as a seismic observation system suitable for a volcanic environment. A three-component sensor was developed that is smaller, lighter, and has a lower natural frequency than the previous one (Tsutsui et al. 2019). The sensors were installed at three locations for array observation, and seismic observations at Sakurajima volcano were conducted for six months from June 2019 (Nakamichi et al., 2022). Earthquakes associated with 267 eruptions were recorded by the optical sensor system during the observation period, and the array analysis results showed that the seismic waves traveled from 1.6 km below sea level, just below the active crater (Nakamichi et al., 2022). A comparative observation was also conducted with a micrometer (Hakusan JU210), wherein noise from lightning surges was detected but there was none in the optical sensor system (Nakamichi et al., 2022). Thus, this system was shown to be suitable for seismic observations in volcanic environments.
We have been developing a borehole housing type three-component sensor of the optical sensor system. In February 2022, this sensor was installed at a depth of 1,980 m in a deep observation well on the premises of the Niigata Institute of Technology to evaluate its observation performance under a high pressure and temperature environment, and the observation is still ongoing. Hirayama et al. (Session S-TT41 of this meeting) presents details of the observation. An automatic seismic detection was performed for continuous waveform data from February to September, 2022. The hypocenters of the detected earthquakes were determined by using particle motions of the three-component waveforms of the borehole sensor. Forty-seven earthquakes were located in the region around the borehole.
This work was supported by MEXT "Integrated Program for Next Generation Volcano Research and Human Resource Development". We sincerely thank the Niigata Institute of Technology for permitting to use the observation well and observation hut.
References:
Yoshida et al., “Real-time displacement measurement system using phase-shifted optical pulse interferometry: Application to a seismic observation system,” Jpn. J. Appl. Phys., Vol.55, No.2, Article No.022701, 2016
Ohe et al., “Verification of principle of a new vibrating sensor with optical interferometry and the application possibility,” Trans. Soc. Instrum. Control Eng., Vol.54, No.1, pp. 111-117, 2018 (in Japanese).
Tsutsui et al., “Feasibility study ona multi-channeled seismometer system with phase-shifted optical interferometry for volcanological observations,” J. Disaster Res., Vol.14, No.4, pp. 592-603, 2019.
Nakamichi et al., "A half-year long observation at Sakurajima volcano, Japan using a Multi-Channeled Seismometer System with Phase-Shifted Optical Interferometry" J. Disaster Res., Vol.17, No.5, pp. 670-682, 2022.
In the Integrated Program for Next Generation Volcano Research and Human Resource Development, the B2-2 project—“Development of a multi-channeled seismometer system with phase-shifted optical interferometry for volcanological observations”—set out to develop an optical sensor as a seismic observation system suitable for a volcanic environment. A three-component sensor was developed that is smaller, lighter, and has a lower natural frequency than the previous one (Tsutsui et al. 2019). The sensors were installed at three locations for array observation, and seismic observations at Sakurajima volcano were conducted for six months from June 2019 (Nakamichi et al., 2022). Earthquakes associated with 267 eruptions were recorded by the optical sensor system during the observation period, and the array analysis results showed that the seismic waves traveled from 1.6 km below sea level, just below the active crater (Nakamichi et al., 2022). A comparative observation was also conducted with a micrometer (Hakusan JU210), wherein noise from lightning surges was detected but there was none in the optical sensor system (Nakamichi et al., 2022). Thus, this system was shown to be suitable for seismic observations in volcanic environments.
We have been developing a borehole housing type three-component sensor of the optical sensor system. In February 2022, this sensor was installed at a depth of 1,980 m in a deep observation well on the premises of the Niigata Institute of Technology to evaluate its observation performance under a high pressure and temperature environment, and the observation is still ongoing. Hirayama et al. (Session S-TT41 of this meeting) presents details of the observation. An automatic seismic detection was performed for continuous waveform data from February to September, 2022. The hypocenters of the detected earthquakes were determined by using particle motions of the three-component waveforms of the borehole sensor. Forty-seven earthquakes were located in the region around the borehole.
This work was supported by MEXT "Integrated Program for Next Generation Volcano Research and Human Resource Development". We sincerely thank the Niigata Institute of Technology for permitting to use the observation well and observation hut.
References:
Yoshida et al., “Real-time displacement measurement system using phase-shifted optical pulse interferometry: Application to a seismic observation system,” Jpn. J. Appl. Phys., Vol.55, No.2, Article No.022701, 2016
Ohe et al., “Verification of principle of a new vibrating sensor with optical interferometry and the application possibility,” Trans. Soc. Instrum. Control Eng., Vol.54, No.1, pp. 111-117, 2018 (in Japanese).
Tsutsui et al., “Feasibility study ona multi-channeled seismometer system with phase-shifted optical interferometry for volcanological observations,” J. Disaster Res., Vol.14, No.4, pp. 592-603, 2019.
Nakamichi et al., "A half-year long observation at Sakurajima volcano, Japan using a Multi-Channeled Seismometer System with Phase-Shifted Optical Interferometry" J. Disaster Res., Vol.17, No.5, pp. 670-682, 2022.