Section: New Results

High Performance methods for solving wave equations

Forward and adjoint simulations of seismic wave propagation on fully unstructured hexahedral meshes

Participants : Daniel Peter, Dimitri Komatitsch, Yang Luo, Roland Martin, Nicolas Le Goff, Emanuelle Casarotti, Pieyre Le Loher, Federica Magnoni, Qinya Liu, Céline Blitz, Tarje Nissen-Meyer, Piero Basini, Jeroen Tromp.

In [30] , we present forward and adjoint spectral-element simulations of coupled acoustic and (an)elastic seismic wave propagation on fully unstructured hexahedral meshes. Simulations benefit from recent advances in hexahedral meshing, load balancing and software optimization. Meshing may be accomplished using a mesh generation tool kit such as CUBIT, and load balancing is facilitated by graph partitioning based on the SCOTCH library. Coupling between fluid and solid regions is incorporated in a straightforward fashion using domain decomposition. Topography, bathymetry and Moho undulations may be readily included in the mesh, and physical dispersion and attenuation associated with anelasticity are accounted for using a series of standard linear solids. Finite-frequency Fréchet derivatives are calculated using adjoint methods in both fluid and solid domains. The software is benchmarked for a layercake model. We present various examples of fully unstructured meshes, snapshots of wavefields and finite-frequency kernels generated by Version 2.0 ‘Sesame’ of our widely used open source spectral-element package SPECFEM3D.

Fluid-solid coupling on a cluster of GPU graphics cards for seismic wave propagation

Participant : Dimitri Komatitsch.

In [28] , we develop a hybrid multiGPUs and CPUs version of an algorithm to model seismic wave propagation based on the spectral-element method in the case of models of the Earth containing both fluid and solid layers. Thanks to the overlapping of communications between processing nodes on the computer with calculation by means of non-blocking message passing, we obtain excellent weak scalability of this finite-element code on a cluster of 192 GPUs and speedup factors of more than one order of magnitude compared to the same code run on a cluster of traditional CPUs. This enables us to show a new geophysical phenomenon concerning wave propagation of diffracted shear waves in a layer called D” located at the base of the Earth's mantle, namely that in this layer the transverse and radial components of these waves can undergo a relative shift even in an isotropic Earth model, whereas this observation in real seismological data was interpreted until now as an indication of the presence of anisotropy in this layer.