קולוקוויום בחוג לגאופיזיקה: Shallow Seismic Methods Using Distributed Acoustic Sensing

Zoom: https://tau-ac-il.zoom.us/j/87073901428?pwd=Zay3aB8aBEigEH9SC4iEU9pByK9FCN.1

​

Abstract:

Distributed Acoustic Sensing (DAS) has emerged as a promising technology that employs optical fibers for high-resolution seismic sensing, offering advantages over conventional sensors in affordability, ease of deployment, permanent installation, and integration with existing infrastructures. This work investigates the capabilities of DAS in near-surface seismic applications across three key research areas. 

First, critical aspects and limitations affecting the quality and performance of shallow DAS data acquisition are examined in various applications. The uniaxial strainmeter properties inherent to DAS are leveraged to address challenges in directional sensing and wave-mode separation. While DAS data generally correlate with traditional sensor data, limitations like the gauge-length effect, measurement directivity, and saturation at near offsets can degrade data quality, limit ultra-shallow resolution, and constrain source directivity. To mitigate these limitations, solutions such as optimized optical parameters, adapted field acquisition strategies, and refined data processing workflows are proposed. 

Next, a comprehensive shallow velocity analysis is conducted using DAS to obtain 2D and 1D P- and S-wave velocity models under various acquisition setups, including horizontal, vertical, and deviated DAS deployments in surface conduits and shallow boreholes. Findings highlight the significant impact of fiber coupling on the signal-to-noise ratio (S/N), emphasizing the need for adequate planning. In both horizontal conduits and vertical boreholes, infilling provides a viable coupling solution. For deviated boreholes, installation inside casing yields suboptimal coupling, but improved deployment protocols may yield high-frequency data useful for velocity-model building and imaging. Comparisons with three-component (3C) geophones confirm DAS as a viable tool for shallow velocity analysis. 

Finally, the effective use of DAS for subsurface source location and void imaging is demonstrated. Utilizing P- and S-wave velocity models derived from DAS data, a subsurface source is successfully located through traveltime error minimization, and a shallow void is accurately imaged using diffraction imaging.
 

מארגן האירוע: ד"ר אריאל ללוש