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Session: Filling the Data Gap: Ocean-bottom Sensing with Fiber-optic Cables - I

Type: Oral

Date: 10/9/2024

Time: 12:45 PM

Room: Stanley Park Ballroom

DAS Observation for High-frequency Tsunamis Excited Near Torishima Island, Japan

Various types of wavefield have been captured by submarine fiber optic cables, including earthquake and ocean waves. However, tsunami signals have been less captured because whether their observations depend on experimental periods and locations for distributed acoustic sensing (DAS). In southern Japan on October 8, 2023 (UT), sea level changes due to tsunamis were observed by tide gauges, and the tsunami generation is likely to be related to activities of submarine volcanoes. We observed the tsunami signals in the continuous records of DAS off Muroto in southern Japan. In this study, to investigate the characteristics of the tsunami signals, we calculate the frequency-dependent phase velocities, and compare the waveforms with those observed at nearby absolute pressure gauges (APGs).

In the DAS records, coherent signals propagating landwards are observed in the northern part of the submarine cable. The dominant frequency is 6–30 mHz. The frequency-dependent propagation velocities of the observed signals correspond to those of infragravity waves (i.e., deep water waves, ocean surface gravity waves), and the infragravity waves are categorized into high-frequency tsunamis.

We also estimated time-series of the tsunami generation at the source location. Relatively high frequency components within high-frequency tsunamis are excited in early stage of the volcanic activities, and their frequency components are shifted to middle and low ones in later stages. This indicates that the volcanic activities tend to be large at the later stage. The obtained features of the time-series were consistent with those using records of the APGs. Our results indicate that DAS records are useful for detecting tsunami propagations and also elucidating excitation mechanisms of tsunamis.

Data citation

DONET: doi:10.17598/NIED.0008

Acknowledgement

This work was supported by JSPS KAKENHI Grant No. JP21H05202, JP21H05204 in Scientific Research on Transformative Research Areas “Science of Slow-to-Fast earthquakes”.

Presenting Author: Takashi

Additional Authors