Elastic time-reverse imaging of backscattered surface-wave data

Imaging shallow near-vertical or short-wavelength structure using seismic data is an important goal in near-surface geophysical applications. Numerous seismic analysis approaches use backscattered analysis of surface waves for these purposes; however, there is a need for new associated frameworks that can take advantage of these events to generate interpretable images in the depth-migrated domain. By drawing a connection with elastic time-reverse imaging (E-TRI) approaches developed for microseismic event analysis, an efficient elastic migration approach is developed that uses two adjoint wavefields defined by partitioned outward-propagating transmission and inward-propagating scattered surface-wave data. Subsurface images are generated by applying the energy-norm imaging condition that correlates temporally and spatially colocated energy throughout the two time-reversed adjoint wavefield domains. Synthetic tests highlight the ability of the E-TRI framework to image shallow (quasi)vertical subsurface discontinuities. Results from a field test using near-surface seismic data acquired in the Majes region of Arequipa, Peru, demonstrate the ability of the E-TRI framework to highlight short-wavelength structure identified in a parallel elastic full-waveform inversion analysis. The results suggest that the E-TRI technique should be applicable in a range of near-surface geotechnical and environmental applications.