Section: New Results

Efficient 3D frequency-domain seismic modeling with a parallel block low-rank (BLR) direct solver

Participants : Patrick Amestoy [INPT-IRIT, University of Toulouse] , Romain Brossier [ISTerre, University of Grenoble-Alpes] , Alfredo Buttari [CNRS-IRIT, University of Toulouse] , Jean-Yves L'Excellent, Théo Mary [UPS-IRIT, University of Toulouse] , Ludovic Métivier [ISTerre-JK-CNRS] , Alain Miniussi [Geoazur-CNRS-UNSA] , Stéphane Operto [Geoazur-CNRS-UNSA] , Alessandra Ribodetti [Geoazur-CNRS-UNSA] , Jean Virieux [ISTerre-UJF, University of Grenoble-Alpes] , Clément Weisbecker [INPT-IRIT, now at LSTC] .

Three-dimensional frequency-domain full waveform inversion (FWI) of fixed-spread data can be efficiently performed in the visco-acoustic approximation when seismic modeling is based on a sparse direct solver. Based on the work in [3] and its extension to a parallel environment, we studied the application of a parallel algebraic Block Low-Rank (BLR) multifrontal solver providing an approximate solution of the time-harmonic wave equation with a reduced operation count, memory demand, and volume of communication relative to the full-rank solver. We analyzed the parallel efficiency and the accuracy of the solver with a realistic FWI case [19] . The application of this parallel BLR solver to a real data case from the North Sea for full waveform inversion of ocean-bottom cable data was also presented in [18] , where a multiscale frequency-domain FWI is applied by successive inversions of 11 discrete frequencies in the 3.5Hz-10Hz frequency band. The velocity model built by FWI reveals short-scale features such as channels, scrapes left by drifting icebergs, fractures and deep reflectors below the reservoir level, alhough the presence of gas in the overburden. The quality of the FWI results is controlled by time-domain modeling and source wavelet estimation. This work was done in the context of an on-going collaboration with the Seiscope consortium (https://seiscope2.obs.ujf-grenoble.fr/?lang=en? ).