10:15 〜 10:30
[SSS03-06] Development of seismic interferometry analysis for DAS data on a seafloor cable to determine shallow S-wave velocity structure with spatially high resolution.
キーワード：Distributed acoustic sensing、地震波干渉法、S波地震波速度構造、海底ケーブル、堆積層と上部地殻、Frequency wavenumber フィルター
Accurate S-wave velocity structures (Vs) of sediments and the uppermost crust in the landward slope of a subduction zone are indispensable information for elucidating the dynamics of the overriding plate. In the subduction zone of the Japan trench, spatially high-resolution P-wave velocity (Vp) structures of sediment and upper crust have already been obtained by the recent development of detailed seismic surveys (Miura et al., 2003; Takahashi et al., 2004). In contrast, reliable estimation of high-resolution Vs structures has been still limited.
In recent years, distributed acoustic sensing (DAS) measurements started being applied to seismic observation, which enables us to measure strain velocities with spatially very high resolution over a long distance. Spica et al. 2020 estimated the Vs structure of shallow sediments (down to 3 km) by applying the frequency–wavenumber (FK) analysis, using the seafloor DAS measurement obtained off the Sanriku coast of Japan. It is noted that this estimation of Vs structures was limited to a shallow portion of sediments.
This study estimated an S-wave velocity (Vs) structure of sediment and upper crust off Sanriku, Japan, using 13-hr distributed acoustic sensing (DAS) data. We grouped the DAS data into 10-km-long subarrays with 75% overlaps. After applying the frequency-wavenumber (FK) filtering to enhance surface waves effectively, we applied seismic interferometry. Phase velocities of the fundamental- and first higher-mode Rayleigh waves were clearly estimated, and one-dimensional Vs structures for each subarray were determined. The obtained 2-D map of Vs structure was interpreted to represent detailed structures of sediments and crust. The upper sediment layer gets thick seawards, and the discontinuity between sediment and crust layers at depths of 3–7 km shows non-negligible lateral heterogeneities. In conclusion, we succeeded in imaging the structure of the deep region of sediments and the uppermost crust in a marine area with a higher lateral resolution by applying seismic interferometry with FK filtering to DAS data over a period of 13 hours.
In recent years, distributed acoustic sensing (DAS) measurements started being applied to seismic observation, which enables us to measure strain velocities with spatially very high resolution over a long distance. Spica et al. 2020 estimated the Vs structure of shallow sediments (down to 3 km) by applying the frequency–wavenumber (FK) analysis, using the seafloor DAS measurement obtained off the Sanriku coast of Japan. It is noted that this estimation of Vs structures was limited to a shallow portion of sediments.
This study estimated an S-wave velocity (Vs) structure of sediment and upper crust off Sanriku, Japan, using 13-hr distributed acoustic sensing (DAS) data. We grouped the DAS data into 10-km-long subarrays with 75% overlaps. After applying the frequency-wavenumber (FK) filtering to enhance surface waves effectively, we applied seismic interferometry. Phase velocities of the fundamental- and first higher-mode Rayleigh waves were clearly estimated, and one-dimensional Vs structures for each subarray were determined. The obtained 2-D map of Vs structure was interpreted to represent detailed structures of sediments and crust. The upper sediment layer gets thick seawards, and the discontinuity between sediment and crust layers at depths of 3–7 km shows non-negligible lateral heterogeneities. In conclusion, we succeeded in imaging the structure of the deep region of sediments and the uppermost crust in a marine area with a higher lateral resolution by applying seismic interferometry with FK filtering to DAS data over a period of 13 hours.