Application of a complete workflow for 2D elastic full-waveform inversion to recorded shallow-seismic Rayleigh waves

The S-wave velocity of the shallow subsurface can be inferred
from shallow-seismic Rayleigh waves. Traditionally, the disper-
sion curves of the Rayleigh waves are inverted to obtain the (local)
S-wave velocity as a function of depth. Two-dimensional elastic
full-waveform inversion (FWI) has the potential to also infer
lateral variations. We have developed a novel workflow for the
application of 2D elastic FWI to recorded surface waves. During
the preprocessing, we apply a line-source simulation (spreading
correction) and perform an a priori estimation of the attenuation
of waves. The iterative multiscale 2D elastic FWI workflow con-
sists of the preconditioning of the gradients in the vicinity of the
sources and a source-wavelet correction. The misfit is defined
by the least-squares norm of normalized wavefields. We apply our
workflow to a field data set that has been acquired on a predomi-
nantly depth-dependent velocity structure, and we compare the
reconstructed S-wave velocity model with the result obtained
by a 1D inversion based on wavefield spectra (Fourier-Bessel ex-
pansion coefficients). The 2D S-wave velocity model obtained by
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FWI shows an overall depth dependency that agrees well with the
1D inversion result. Both models can explain the main character-
istics of the recorded seismograms. The small lateral variations in
S-wave velocity introduced by FWI additionally explain the lateral
changes of the recorded Rayleigh waves. The comparison thus
verifies the applicability of our 2D FWI workflow and confirms
the potential of FWI to reconstruct shallow small-scale lateral
changes of S-wave velocity.