Full-wavefield modeling and reverse time migration of laser ultrasound data: A feasibility study

Laser ultrasound (LU) data acquired on cylindrical core samples effectively probe the physical properties of geologic materials. Although most LU analyses focus on estimating and inverting traveltimes of direct arrivals, it is important to recognize that LU data sets can have rich wavefield coda and can now be acquired with a sufficient spatial density to enable the application of exploration seismic full-wavefield techniques such as reverse time migration (RTM) and, potentially, full-waveform inversion (FWI). We have developed a feasibility study that examines the applicability of 2D acoustic forward modeling and 2D RTM analyses on laboratory LU data acquired on cylindrical polymer samples. Forward-modeled waveforms from our numerical tests matched the kinematics of the LU body waves measured through homogeneous samples, as well as the scattered wavefield generated by fractures induced in an otherwise homogeneous medium. The scattered wavefield is then used in an RTM scheme to directly image millimeter-scale fracture structure.