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Imaging Near-Coast Subsurface With Distributed Acoustic Sensing and Double Beamforming

Description: 

An Ocean-bottom Distributed Acoustic Sensing unit collected four-month data from a telecommunication fiber cable in the coastal Oregon region. The energy of the microseisms is concentrated below 2 Hz and is generated by ocean wave-solid earth interactions. We extract clear surface waves propagating both landward and seaward using a cross-correlation scheme. The quasi-linear geometry of the cable enables applications of conventional slant stack and 1D double beamforming to measure phase velocity. We generate dispersion curves from Cross Correlation Functions (CCFs) with 500 virtual receiver channels with slant stack. A continuous phase velocity profile is acquired by moving the virtual source along the array. With 1D double beamforming, we first define source beam and receiver beam pairs along the cable. Presuming phase velocities of both beams, we stack travel-time-adjusted CCFs of all the source-receiver pairs within the beams. Good velocity estimates stack CCFs constructively, and we test numerous pairs of inputs in search of the best velocities in the source and receiver beams respectively, which return the highest CCF amplitude. Repeating the same procedure with different beam pairs along the array and averaging over all the available estimations, we retrieve a 2D velocity profile on the region. Finally, we separately invert both velocity profiles for subsurface shear wave velocity models. By comparing the two models, we find good agreement on submarine structures and anomalies. We combine two models with respect to their uncertainties to present a final model of shear wave velocity.

Session: Understanding Earth Systems with Fiber-optic Cables [Poster]

Type: Poster

Date: 4/19/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Yaolin Miao

Student Presenter: Yes

Invited Presentation: 

Authors