1. High‐Frequency Tsunamis Excited Near Torishima Island, Japan, Observed by Distributed Acoustic Sensing.
- Author
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Tonegawa, T. and Araki, E.
- Subjects
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TSUNAMIS , *OCEAN waves , *GRAVITY waves , *FIBER optic cables , *GEOPHYSICAL instruments , *PHASE velocity - Abstract
Recent distributed acoustic sensing (DAS) experiments in ocean areas throughout the world have accumulated records for various wavefields. However, there are few tsunami records because tsunami observation depends on the DAS experimental period and its location. From continuous DAS records, we found tsunami signals at a frequency band of 5–30 mHz, which correspond to high‐frequency components of tsunamis and their propagation velocities differ from low‐frequency tsunamis. We estimated time series of the tsunami excitations at the source using the DAS records, which are consistent with those using records of ocean‐bottom absolute pressure gauges. Our study suggests that DAS records can be used for detecting tsunami propagations in the regions where other geophysical instruments are not available, and contribute to elucidating their excitation mechanisms. Plain Language Summary: Using distributed acoustic sensing (DAS) techniques, various types of wavefields, such as earthquake and ocean waves, have been captured by submarine fiber optic cables. However, the recording of tsunamis has been limited, as their observation depends on the timing and location of the DAS experiments. On 8 October 2023, in southern Japan, changes in sea level attributable to tsunamis were detected by tide gauges. Continuous DAS records in southern Japan have enabled the capture of signals associated with these tsunamis. The observed signals exhibit frequency‐dependent propagation velocities, which correspond to infragravity waves. These are essentially deep water waves or ocean surface gravity waves, representing the high‐frequency components of tsunamis. Using the DAS records alone, we were able to estimate the time‐series of the tsunami generation at the source location. The features obtained from the time‐series were consistent with those from records of absolute pressure gauges on the seafloor deployed in southwestern Japan. Our findings demonstrate the utility of DAS records in detecting tsunami propagations and also elucidating excitation mechanisms of tsunamis. Key Points: The countinuous records of our distributed acoustic sensing measuresment capture tsunami‐related signalsThe phase velocity dispersion of the obtained signals matches that of infragravity waves (high‐frequency tsunamis)The time‐series of the tsunami generation obtained by the cable data are consistent with those from nearby absolute pressure gauges [ABSTRACT FROM AUTHOR]
- Published
- 2024
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