Global Scale Full-Waveform Inversion Using Wavefield Adapted Meshes

Abstract:

With the exponential increase in waveform data availability, full-waveform inversion (FWI) can reveal the Earth's subsurface with unprecedented accuracy. Exploiting such large quantities of waveform data, however, carries a significant computational burden which which impedes progress, despite growing super-computing resources. Algorithmic and technological innovations are thus essential to accelerate the progress of seismic waveform inversions.

In this contribution, we present an approach which combines the usage of wavefield adapted meshes [1] with a stochastic optimization scheme [2]. This twofold strategy allows us to a) reduce the computational cost of both forward and adjoint simulations by an order of magnitude, and b) reduce the number of required simulations. Wavefields in laterally smooth media can be meshed in a way that their smoothness is exploited, allowing for meshes with far less elements. By optimally designing a unique mesh for each source in the inversion, the simulation cost can be greatly reduced. The discrete adjoint approach allows for accurate computation of gradients using the wavefield adapted meshes. By using a dynamic mini-batch trust-region L-BFGS optimization scheme the earthquake catalog is dynamically subsampled throughout the inversion, ensuring a good spatial coverage in each iteration. An additional benefit of the dynamic mini-batch approach is that the computational cost of the inversion is no longer directly linked to the number of earthquakes used in the inversion, allowing for the usage of much more data, without significant extra cost.

We demonstrate the before-mentioned approach along with the status of our fully automatic global-scale real data FWI.


[1] S. Thrastarson, M. van Driel, L. Krischer, C. Boehm, M. Afanasiev, DP. van Herwaarden, A. Fichtner, Accelerating numerical wave propagation by wavefield adapted meshes. Part II: full-waveform inversion, Geophysical Journal International, https://doi.org/10.1093/gji/ggaa065
[2] DP. van Herwaarden, C. Boehm, M. Afanasiev, S. Thrastarson, L. Krischer, J. Trampert, A. Fichtner, Accelerated full-waveform inversion using dynamic mini-batches, Geophysical Journal International, https://doi.org/10.1093/gji/ggaa079