High-Resolution Imaging of Submarine Structures and Ocean Microseism Sources With Distributed Acoustic Sensing
Description:
Ocean-generated microseism is a predominant source of seismic noise on Earth. It reflects the dynamics of ocean waves and Earth’s shallow structures and has been commonly used for studying both of them. However, quantitative understanding of such noise and its applications for seismic purposes are still limited by the sparsity of submarine seismic instrumentations. Distributed acoustic sensing (DAS) is offering a cost-effective solution to this limitation by converting submarine fiber-optic cables into dense seismic arrays.
In November 2021, a 4-day submarine DAS experiment was conducted in offshore Oregon. In cross-correlations of ambient noise records, Scholte waves are clearly observed in the frequency band of 0.1-1 Hz. The precise Scholte wave phase velocity dispersion is inverted for a high-resolution subsurface shear velocity model. The result reveals several sediment basins whose depths and shapes are consistent with interfaces in previous seismic survey profiles. We also measure landward/oceanward signal amplitude ratios in cross-correlations for different channel pairs and implement a Bayesian inversion for the spatial distribution of microseism sources. While the deep ocean produces strongest sources for long-period microseism (< 0.2 Hz), coastal sources become dominant for short-period microseism (> 0.2 Hz) and the location is shallower when the frequency is higher. The retrieval of high-resolution noise source spatial variations provides new insight into ocean wave and microseism noise models.
We successfully used signal travel times to image subsurface velocity structures and amplitude asymmetry to unravel the distribution of microseism sources along the DAS array. The local noise field can be reconstructed by considering both site effects of sediments and sources related to ocean waves. The findings greatly advance our knowledge of the ambient noise field and how it can be employed to investigate the marine environment.
Session: Understanding Earth Systems with Fiber-optic Cables
Type: Oral
Date: 4/19/2023
Presentation Time: 08:30 AM (local time)
Presenting Author: Jiaqi Fang
Student Presenter: Yes
Invited Presentation:
Authors
Jiaqi Fang Presenting Author Corresponding Author jfang@caltech.edu California Institute of Technology |
Yan Yang yanyang@caltech.edu California Institute of Technology |
Ethan Williams efwillia@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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High-Resolution Imaging of Submarine Structures and Ocean Microseism Sources With Distributed Acoustic Sensing
Category
Understanding Earth Systems with Fiber-optic Cables