Numerical studies of information about elastic parameter sets in non-linear elastic wavefield inversion schemes

Abstract

Non-linear elastic wavefield inversion is a powerful method for estimating elastic parameters for physical constraints that determine subsurface rock and properties. Here, I introduce six elastic-wave velocity models by reconstructing elastic-wave velocity variations from real data and a 2D elastic-wave velocity model. Reflection seismic data information is often decoupled into short and long wavelength components. The local search method has difficulty in estimating the longer wavelength velocity if the starting model is far from the true model, and source frequencies are then changed from lower to higher bands (as in the ‘frequency-cascade scheme’) to estimate model elastic parameters. Elastic parameters are inverted at each inversion step (‘simultaneous mode’) with a starting model of linear P- and S-wave velocity trends with depth. Elastic parameters are also derived by inversion in three other modes – using a P- and S-wave velocity basis (‘VP VS mode’); P-impedance and Poisson’s ratio basis (‘IP Poisson mode’); and P- and S-impedance (‘IP IS mode’). Density values are updated at each elastic inversion step under three assumptions in each mode. By evaluating the accuracy of the inversion for each parameter set for elastic models, it can be concluded that there is no specific difference between the inversion results for the VP VS mode and the IP Poisson mode. The same conclusion is expected for the IP IS mode, too. This gives us a sound basis for full wavelength elastic wavefield inversion.