A Half-Year Long Observation at Sakurajima Volcano, Japan Using a Multi-Channeled Seismometer System with Phase-Shifted Optical Interferometry

Abstract

The performance of a multi-channel seismometer system with phase-shifted optical interferometry was improved by newly introduced sensors and a processing unit. The current version of the system consists of three optical wired seismometers and the unit. We deployed the system at Sakurajima Volcano and successfully operated it from June to December 2019. As the Sakurajima Volcano frequently erupts, a number of eruption events were observed during the observation period, as were a number of lightning strikes. In this study, we evaluated the observation performance of the volcanic earthquake and the noise caused by the lightning, using the spectrum and amplitude of the waveform. The results show that this sensor can observe earthquakes caused by eruptions as well as ordinary seismometers do. When the lightning struck, pulsed noise with power in a wide frequency band was observed in the existing seismometer, but not in the new sensor. Therefore, the observation was not affected by lightning. In addition, this system was found to be effective in the array analysis of volcanic earthquakes.