Seismic Monitoring and S-wave Velocity Structure Analysis of the Hunga Volcano with Distributed Acoustic Sensing on an Active Telecommunication Cable

Monitoring submarine volcanoes is critical for mitigating volcanic disasters, as highlighted by the large 2022 eruption of the Hunga volcano. However, seafloor seismic observations using Ocean Bottom Seismometers (OBS) face challenges in cost and real-time data transmission. This study tests out volcano monitoring using Distributed Acoustic Sensing (DAS) technology on active seafloor telecommunication cables.
We conducted a seismic observation campaign from August to December 2025 using the domestic telecommunication cable in the Kingdom of Tonga. By utilizing a cable monitoring solution that employs Wavelength Division Multiplexing (WDM) technology, the sensing signal (1572.06 nm) coexisted with active commercial traffic (1550 nm) within a single optical fiber. To ensure the accuracy of the seismic array processing, we determined the precise cable geometry using signals from an airgun survey conducted by a collaborative research team led by the University of Tasmania. Furthermore, we performed S-wave velocity structure analysis using seismic interferometry.
Analysis of the recorded data showed that the background noise level in the 1-20 Hz band was comparable to our previous observations on dark fibers, confirming the feasibility of DAS with WDM for high-sensitivity monitoring. Our DAS system enabled high-sensitivity observations as close as 16 km from Hunga volcano, while the nearest terrestrial seismometer is located approximately 70 km away from the volcano. Using a dataset consisting of daily 30-minute recordings over three months, an automated detection algorithm successfully identified approximately 550 seismic events. The observation system maintained a high Signal-to-Noise Ratio up to 70 km from the landing station, providing valuable data in regions previously uncovered by terrestrial networks. These results demonstrate that the existing global submarine cable infrastructure, even in use for communication, can be transformed into a high-density, real-time monitoring network for submarine volcanoes.

 

Acknowledgments
This study used the data obtained by the collaboration with FiberSense Ltd., Tonga Cable Ltd., University of Tasmania, Japan International Cooperation Agency and Tonga Geological Services. This research was supported by Science and Technology Research Partnership for Sustainable Development (SATREPS: No. JPMJSA2309), Japan Science and Technology Agency (JST)/Japan International Cooperation Agency (JICA).