A parameterization study for elastic VTI Full Waveform Inversion of hydrophone components: synthetic and North Sea field data examples

Abstract

Choosing the right parameterization to describe a transversely isotropic medium with a vertical symmetry axis (VTI) allows us to match the scattering potential of these parameters to the available data in a way that avoids potential tradeoff and focus on the parameters to which the data are sensitive. For 2-D elastic full waveform inversion in VTI media of pressure components and for data with a reasonable range of offsets (as with those found in conventional streamer data acquisition systems), assuming that we have a kinematically accurate NMO velocity (vnmo) and anellipticity parameter η (or horizontal velocity, vh) obtained from tomographic methods, a parameterization in terms of horizontal velocity vh, η and ε is preferred to the more conventional parameterization in terms of vh, δ and ε. In the vh, η, ε parameterization and for reasonable scattering angles (<60o), ε acts as a “garbage collector” and absorbs most of the amplitude discrepancies; between modeled and observed data, more so when density ρ and shear-wave velocity vs are not inverted for (a standard practice with streamer data). On the contrary, in the vv, δ, ε parameterization, ε is mostly sensitive to large scattering angles, leaving vv exposed to strong leakages from ρ mainly. There assertions will be demonstrated on the synthetic Marmousi II as well as a North Sea OBC dataset, where inverting for the horizontal velocity rather than the vertical velocity yields more accurate models and migrated images.