ANISOTROPIC TRAVELTIME TOMOGRAPHY

摘要: Velocity estimation technique using seismic data is often based on time/distance equations which are independent of direction, but useful results have been obtained over the years from these isotropic estimates. Nevertheless, if velocities significantly direction-dependent, then assumption may lead to serious structural interpretation errors. Additionally, information angle-dependence a better understanding lithology rocks under measurement. VSP and cross-well each lack necessary aperture estimate more than two velocity parameters for wave type, straddle symmetry axis, be usefully chosen direct (from time-and-distance measurements along axis) NMO differential time-offset measurements). These sets define ellipses, provide intermediate models variation with angle can later assembled translated into estimates elastic moduli scrutiny. The inversion proposed in this paper simple extension well-known schemes it conceptually identical all types. Examples shown illustrate application synthetic field P-wave data. examples demonstrate three important points:more » (a) when anisotropy estimated by iterative techniques such as conjugate gradients, early termination iterations produce artificial anisotropy; (b) different components subject type artifacts because differences ray coverage; (c) even though most do not elliptical dispersion relations, represent step full characterization properties.« less