Automatic multicomponent image registration

Abstract

Multicomponent seismic images are composed of different combinations of downgoing and upgoing wavefields. Each wave mode has different propagation velocity and polariza- tion direction and thus carries unique, direction-dependent information about the subsurface. Differences in propagation velocity cause events in converted- or shear-wave images to appear at later times than the compressional-wave image counterpart. Reflectivities are different for each wave mode and therefore, multicomponent images are not related simply by time shifts. These complications historically required that the alignment, also called registration of corresponding image features be done manually, a tedious process. This thesis devel- ops an approach to automatically register multicomponent images using a smooth dynamic warping algorithm that can be accurate with respect to problems unrelated to time shifts. Interval Vp/Vs ratios can be estimated from derivatives of time shifts that align reflections in multicomponent images, and these Vp/Vs ratios may be used to assess the accuracy of the automatic registration process. To improve the accuracy of estimated time shifts and Vp/Vs ratios, we automatically construct a coarse lattice of points located on reflections with high amplitudes, and then estimate time shifts at only those points. By adjusting the coarseness of the lattice, we trade off resolution of changes in Vp/Vs with increased accuracy in Vp/Vs estimates. The result is an efficient, robust, and automatic method for multicomponent image registration.