Abstract
SUMMARYWe present a novel full-waveform inversion (FWI) approach which can reduce the computational cost by up to an order of magnitude compared to conventional approaches, provided that variations in medium properties are sufficiently smooth. Our method is based on the usage of wavefield adapted meshes which accelerate the forward and adjoint wavefield simulations. By adapting the mesh to the expected complexity and smoothness of the wavefield, the number of elements needed to discretize the wave equation can be greatly reduced. This leads to spectral-element meshes which are optimally tailored to source locations and medium complexity. We demonstrate a workflow which opens up the possibility to use these meshes in FWI and show the computational advantages of the approach. We provide examples in 2-D and 3-D to illustrate the concept, describe how the new workflow deviates from the standard FWI workflow, and explain the additional steps in detail.
Highlights
The principal motivation of this contribution is a first proof of concept, showing that wavefield-adapted meshes combined with the discrete adjoint technique may lead to an full-waveform inversion (FWI) implementation that requires significantly lower computational resources, in cases where variations in medium properties are sufficiently smooth
The elements in the adaptive mesh refinements (aAMR) mesh are aligned with the wavefield propagating from the source location, and the wavefields are approximately identical on both meshes
In this work we demonstrate where this approach is applicable to FWIs and where it starts to break down
Summary
SUMMARY We present a novel full-waveform inversion approach which can reduce the computational cost by up to an order of magnitude compared to conventional approaches, provided that variations in medium properties are sufficiently smooth. By adapting the mesh to the expected complexity and smoothness of the wavefield, the number of elements needed to discretise the wave equation can be greatly reduced. Either using the adjoint method (e.g., Tarantola 1988; Tromp et al 2005; Fichtner et al 2006; Plessix 2006) or the scattering-integral method (e.g., Chen et al 2007b,a) Both methods compute a gradient with one additional wavefield simulation. Today it is technically possible to utilize the full information from waveforms recorded at seismic stations distributed around the globe in a broad frequency range To exploit this information, the physical equations describing how a wavefield propagates away from a source and through a potentially complex medium need to be solved accurately.
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