Three-dimensional prestack plane-wave Kirchhoff depth migration in laterally varying media

Migration is a process by which we obtain images of the earth's subsurface from seismic data. Several migration methods exist. Conventional Kirchhoff depth migration is the often used popular because of its accuracy and efficiency. In this dissertation I describe the development of a new Kirchhoff depth migration technique that uses data in the plane-wave {dollar}(tau{dollar}-p) domain and is therefore computationally more efficient for some seismic acquisition geometries. I present both two dimensional (2-D) and three dimensional (3-D) synthetic and real data examples to demonstrate the accuracy and efficiency of the method. For the 2-D case I used a finite difference solution of the Eikonal equation to compute the required plane-wave travel times while for the 3-D case I used ray tracing. Plane-wave data can be organized into constant ray parameter sections and can be migrated independently. This feature is used to design a parallel algorithm where partial images are generated in several computer nodes and are stacked to produce a final image. The same feature can be used for velocity analysis since different constant ray parameter sections will produce inconsistent images when the wrong velocity model is used. This inconsistency can be observed as the non aligned events in the common image gather (CIG) panels. I used a nonlinear optimization technique called Very Fast Simulated Annealing (VFSA) to find the velocity model that produces the best CIG panels. For 3-D experiments the ray parameter (p) is separated into components in the X and Y directions respectively. The intercept time ({dollar}tau{dollar}) is defined in terms of this vector ray parameter. For the 3-D case I used ray tracing combined with interpolation to compute the gridded plane-wave travel times. The equations for the 3-D ray tracing method are developed and presented here. The 3-D plane-wave Kirchhoff migration algorithm is designed to handle large volumes of data and overlaps computations with data input and output to achieve a higher efficiency. Both the conventional Kirchhoff and plane-wave Kirchhoff 3-D migration methods were applied to Ocean Bottom Seismometer (OBS) data collected along the Pacific coast of Costa Rica, in 1995, by the University of Texas Institute for Geophysics. A comparison of the conventional and plane-wave migrated images and their computation times indicate that improved images were obtained with the new method in a significantly reduced computation time.