Effects of Surface Scattering in Waveform Inversion

Abstract

In full waveform inversion of seismic body waves, the free surface is often ignored on grounds of computational efficiency. We investigate the effect of this simplification for highly irregular topography by means of a synthetic example. Our test model and data conform to a long-offset survey of the upper crust in terms of size and frequency. Random fractal variations are superimposed on a background model. We compute synthetic data for this model and different topographies, and we invert it neglecting the free surface. The resulting waveform models are relatively similar and, for the most part, show a high degree of correlation with the true model. The inversion of the irregular-topography data produces a few strong artifacts at shallow depths, but only a minor decrease in overall resolution. However, both waveform models fail to image below a strong shallow velocity contrast. The results suggest that in this part of the model the incapacity to properly reproduce the reverberations from that contrast without free surface derails both inversions.

High-resolution seismic attenuation imaging from wide-aperture onshore data by visco-acoustic frequency-domain full-waveform inversion

“…For the FWI application presented in this study, we do not make any attempt to model accurately the free-surface effects by cancelling the pressure on the surface. Instead, we set a layer above the topography with a constant velocity of 1600 m s −1 in the manner of Bleibinhaus & Rondenay (2009).…”

A stable high-order perturbation of surfaces method for numerical simulation of diffraction problems in triply layered media

“…We now display results of simulations of a triply layered medium whose scattering returns are governed by (2). As exact solutions are unavailable, to display the spectral accuracy of our Legendre-Galerkin scheme we use the widely-accepted diagnostic of "energy defect"; see e.g.…”

“…The accurate numerical simulation of linear waves interacting with periodic layered media is a crucial capability in many areas of scientific and industrial interest. Examples exist in areas such as geophysics [1,2], materials science [3], imaging [4], oceanography [5], and nanoplasmonics [6,7,8]. The latter includes topics as diverse as extraordinary optical transmission [9], surface enhanced spectroscopy [10], and surface plasmon resonance biosensing [11,12,13,14,15,16].…”