New seismic modelling facilities in MATLAB

Gary F. Margrave

The seismic modelling capabilities available in the CREWES Matlab toolbox have been substantially upgraded. These capabilities expand an already strong interactive facility to bring a large variety of useful tools to the explorationist or researcher.

The v(z) raytracing facility has a fast ray-shooting algorithm that allows an efficient, iterative solution to the two-point raytracing problem. Specialty routines are available to trace P-P and P-S primary reflections for any acquisition geometry (including source gathers, receiver gathers, VSPs, and OBC). Traveltimes and ray parameters are determined but not amplitudes. A general-purpose interface is available to trace arbitrary multi-modes that have any number of mode conversions and up or down legs.

A v(x,z) raytracing capability has been developed that solves the ray tracing differential equation on a 2D grid. This method uses a 4 th order Runge-Kutta solver to create a very general ray-shooting algorithm. Normal incidence raytrace migration and modelling capabilities have been developed using this raytracer.

The acoustic finite-difference facility has been improved and many bugs were fixed. Based on the 2D variable-velocity scalar-wave equation, this modelling facility uses time-stepping to advance a wavefield. Both 2 nd and 4 th order Laplacians are available and Clayton-Engquist absorbing boundaries have been implemented. Any 2D source or receiver geometry can be simulated including such effects as arrays, VSPs, and topography. An exploding reflector option also has been created to allow simple modelling of stacked sections.

An interactive picking facility has been built into the basic seismic viewer. This facility allows interactive normal-incidence raytrace modelling and migration to be done interactively. Picks can be made on depth or time sections and the corresponding raypaths are drawn in depth.