P-wave time-domain signatures in transversely isotropic media
Published:January 01, 2012
The most critical step in extending seismic inversion and processing to anisotropic media is to identify the medium parameters responsible for measured reflection signatures. In chapter 1 it was demonstrated that Thomsen notation makes it possible to reduce the number of parameters that govern P-wave kinematics in VTI media from four to three (VP0, ∈, and δ). Therefore, if amplitude preservation is not an issue, for purposes of P-wave depth imaging (e.g., prestack depth migration) one needs to reconstruct the spatial distributions of those three parameters.
The subject of this chapter is time-domain P-wave processing, which includes normal-moveout (NMO) and dip-moveout (DMO) corrections, prestack and post-stack time migration. As shown here, for laterally homogeneous VTI models above a horizontal or a dipping target reflector, P-wave time-domain signatures depend on the interval values of just two combinations of (VP0, ∈, and δ). Furthermore, both “time-processing” parameters can be recovered from P-wave reflection moveout alone, without using borehole information or multicomponent (S or PS) data.
According to the results of chapter 4, long-spread P-wave moveout in a horizontal VTI layer is controlled by the vertical traveltime (tP0) and two medium parameters, one of which is the NMO velocity commonly measured in seismic processing:
The other parameter is the anisotropy coefficient η, which quantifies the anellipticity of the medium [equation (4.14)]:
Whereas Vnmo2(0) is responsible for the initial slope of the t2(x2)-curve, η determines the deviation of the traveltime function from a hyperbola. If the medium is elliptical (∈ = δ, η = 0),
Figures & Tables
Seismic Signatures and Analysis of Reflection Data in Anisotropic Media, Third Edition
This is a new edition of Ilya Tsvankin’s reference volume on seismic anisotropy and application of anisotropic models in reflection seismology. Seismic Signatures and Analysis of Reflection Data in Anisotropic Media, Geophysical References Series No. 19, provides essential background information about anisotropic wave propagation, introduces efficient notation for transversely isotropic (TI) and orthorhombic media, and identifies the key anisotropy parameters for imaging and amplitude analysis. To gain insight into the influence of anisotropy on a wide range of seismic signatures, exact solutions are simplified in the weak-anisotropy approximation.