Decoding the Submarine Ambient Noise Field with Distributed Acoustic Sensing
Description:
Microseism constitutes a major component of seismic ambient noise on Earth. However, a comprehensive understanding of its generation and propagation were limited by sparse seismic instrumentations in the ocean. Distributed acoustic sensing (DAS) is bridging this gap by enabling direct measurements of microseism sources and seafloor sedimentary structures that host the resulting noise field. In this study, we use DAS data from offshore Oregon to analyze the principal factors that modulate these vibrations, sources and site amplification. With ambient noise tomography, we obtain the subsurface velocity structures and can then calculate the relative surface wave amplification along the DAS array. The microseism source distribution can be inverted from the directional asymmetry of noise cross-correlation signal amplitudes, which determines the energy received by each DAS channel. The integration of these two effects satisfactorily predicts the power spectral density (PSD) observations. At low frequencies, the source heterogeneity is mitigated by minimal attenuation and the site amplification is dominant. Conversely, at high frequencies, the contribution from local sources becomes crucial as well, and the PSD is a composite outcome of both site and source effects. The spatial variations of noise can be explained by the interplay between the bathymetry, sedimentary structures and frequency-dependent ocean wave properties. Consequently, we demonstrate that the ambient noise field on the seafloor is shaped by both geological features below and ocean activities above. Our approach also permits a quantitative evaluation of microseism excitation and offshore site amplification at a local scale, which provides vital insight for harnessing ocean energy and assessing undersea natural hazards.
Session: Marine Seismoacoustics - I
Type: Oral
Date: 5/1/2024
Presentation Time: 05:00 PM (local time)
Presenting Author: Jiaqi
Student Presenter: Yes
Invited Presentation: Yes
Authors
Jiaqi Fang Presenting Author Corresponding Author jfang@caltech.edu California Institute of Technology |
Ethan Williams efwillia@uw.edu University of Washington |
Yan Yang yanyang@caltech.edu California Institute of Technology |
Ettore Biondi ebiondi@caltech.edu California Institute of Technology |
Zhongwen Zhan zwzhan@caltech.edu California Institute of Technology |
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Decoding the Submarine Ambient Noise Field with Distributed Acoustic Sensing
Category
Marine Seismoacoustics