Imaging shallow structure with active-source surface wave signals recorded by distributed acoustic sensing

Distributed acoustic sensing (DAS) is one recently developed seismic acquisition technique that is based on fiber-optic sensing. DAS provides dense spatial spacing that is useful to image shallow structure with surface waves. The 8700-m Distributed Acoustic Sensing (DAS) cable was deployed at Brady's Hot Springs, Nevada in March 2016 and it recorded swept-frequency signals by the vibroseis truck T-Rex excited at about 66 vibe points. The Rayleigh wave excited by the vertical mode of T-Rex was analyzed with the Multichannel Analysis of Surface Waves (MASW) method. Phase velocities between 5 and 20 Hz were successfully extracted for one segment of cable and were employed to build a shear-wave velocity model for the top 50 meters. A surface wave inversion scheme based on the neighborhood algorithm is utilized to invert for shear velocity structure. The spatial variation suggests different sedimentary deposit in shallow depth and it also reveals low velocity in the fault zone.