The role of attenuation in 2D full-waveform inversion of shallow-seismic body and Rayleigh waves

Abstract

Full-waveform inversion (FWI) of Rayleigh waves is attractive for shallow geotechnical investigations due to the high sensitivity of Rayleigh waves to the S-wave velocity structure of the subsurface. In shallow-seismic field data, the effects of anelastic damping are significant. Dissipation results in a low-pass effect as well as frequency-dependent decay with offset. We found this by comparing recorded waveforms with elastic and viscoelastic wave simulation. The effects of anelastic damping must be considered in FWI of shallow-seismic Rayleigh waves. FWI using elastic simulation of wave propagation failed in synthetic inversion tests in which we tried to reconstruct the S-wave velocity in a viscoelastic model. To overcome this, Q-values can be estimated from the recordings to quantify viscoelasticity. Waveform simulation in the FWI then uses these a priori values when inferring seismic velocities and density. A source-wavelet correction, which is inevitable in FWI of field data, can compensate a significant fraction of the residuals between elastically and viscoelastically simulated data by narrowing the signals' bandwidth. This way, elastic simulation becomes applicable in FWI of data from anelastic media. This approach, however, was not able to produce a frequency-dependent amplitude decay with offset. Reconstruction, therefore, was more accurate when using appropriate viscoelastic modeling in FWI of shallowseismic Rayleigh waves. We found this by synthetic inversion tests using elastic forward simulation as well as viscoelastic simulation with different a priori values for Q.

Skeletonized wave equation of surface wave dispersion inversion

“…by (Groos et al, 2014). They concluded that the estimation of a priori quality factors is critical for inverting seismic waves in the near-surface zone .…”

“…Inverting surface waves for the S-wave velocity model fall into two categories: 1) the classical method of inverting dispersion curves (Evison et al, 1959;Park et al, 1998;Xia et al, 2004) for a 1D layered medium, and 2) waveform inversion (Groos et al, 2014;Solano et al, 2014;Dou and Ajo-Franklin, 2014) for 2D and 3D media. The classical method accurately inverts for a 1D S-wave velocity model, but becomes less accurate with increasing lateral heterogeneity in the subsurface velocity model.…”

Individual and Joint 2-D Elastic Full Waveform Inversion of Rayleigh and Love Waves

“…We distribute them along the model surface with an equidistant spacing of 1 m. We place each receiver one grid point below the free surface to ensure an accurate amplitude scaling (Groos, 2013). In case of the P-SV simulations the receivers record the vertical, z , velocity component and in case of the SH simulations they record the horizontal crossline, , velocity component.…”

“…The location of the test site is on a glider air eld in Rheinstetten near Karlsruhe (Germany). We obtain the subsurface model for this location from previous Rayleigh wave FWI studies (Groos, 2013;Groos et al, 2014;Binnig, 2015). Their inversion results suggest a predominantly depth dependent 1-D background model, which is superimposed by a shallow small-scale low-velocity trench.…”

“…In most of the publications Rayleigh waves were used (e.g. Tran et al, 2013;Groos, 2013;Schaefer, 2014), whereas Love waves were only rarely used (Dokter et al, 2014;Pan et al, 2016). Nevertheless,…”