Surface Wave Testing with Distributed Acoustic Sensing Measurements to Estimate the Shear-Wave Velocity and the Small-Strain Damping Ratio

An accurate in-situ estimate of the shear-wave velocity and the small-strain damping ratio profiles is paramount for quantifying the response of soil deposits to dynamic loading. An effective approach relies on the multichannel analysis of surface waves (MASW), which measures the phase velocity and attenuation of Rayleigh waves to derive the stiffness and damping parameters of the soil deposit. This contribution presents results from a MASW survey carried out at Hornsby Bend (Texas), wherein waveforms were recorded simultaneously with a geophone array and a fiber-optic distributed acoustic sensing (DAS) array. DAS is an innovative technology in seismic measurements and monitoring, whose use in geophysics is still limited yet promising. DAS waveforms were processed to extract the Rayleigh wave propagation parameters. Experimental data were then mapped into suitable shear-wave velocity and damping ratio profiles, by means of a Monte Carlo-based inversion algorithm. This study represents the first joint characterization of stiffness and dissipative parameters of a soil deposit based on a fiber-optic array, to our knowledge. The comparison with results from the geophone array demonstrates the reliability of the DAS technology for subsurface characterization. Besides, DAS data exhibit low variability, entailing a high level of accuracy. Therefore, the DAS technology can be successfully used for the joint derivation of the shear-wave velocity and the small-strain damping ratio. It is believed that the diffusion of this technology in geophysical characterization will improve the quality of the in-situ estimates of soil parameters, thus enhancing the reliability of the predicted seismic ground response.