Back to Calendar
Gabriel Fabien-Ouellet, doctoral student at Insitut National de la Recherche Scientifique, presents “Viscoelastic Full Waveform Inversion: Theory, Implementation and Application”.
“Recently, the full waveform inversion community has shown a renewed interest in viscous attenuation. Indeed, viscous attenuation can have a strong impact on seismic wave propagation and is a property of interest in itself. Moreover, with advances on multiparameter inversion, including the Q factor in the inversion is now conceivable. Even though Tarantola developed the theory of viscoelastic FWI from the very beginning, the formulation he used is not readily applicable to the very popular velocity-stress wave equation with standard linear solids. This presentation addresses how viscoelastic FWI can be performed based on this formulation. In the first part, the adjoint state method is applied to the velocity-stress wave equation and the explicit expressions of the misfit gradient for the density and the S- and P- wave velocities and attenuation levels are derived. The second part focuses on the numerical implementation of viscoelastic FWI. Using graphic cards with the programming framework OpenCL, the misfit gradient can be computed very efficiently, showing a speed-up of up to two orders of magnitude over a single threaded CPU implementation. Furthermore, the use of OpenCL in conjunction with MPI allows performing calculations on large clusters of CPUs, GPUs or accelerators. In the last part, the application of viscoelastic FWI to the crosswell monitoring of CO2 geological storage is presented. In particular, we show that the attenuation levels can indeed be recovered by FWI provided that attenuation is strong enough. Results also indicate that the attenuation level is an interesting property to monitor the CO2 plume. The presentation will conclude on future perspectives for viscoelastic FWI.”