Interval velocity analysis using s-g downward-continued data
, by Chuck Sword
The method of CDR tomographic inversion (Sword, 1987) uses reflection
seismic data to find interval velocities. (Recall that CDR stands for
Controlled Directional Reception). A difficulty with this method is
that its objective function is based on one-point ray tracing, where
only the takeoff position and angle of each ray are given; these ray-
paths are unduly influenced by horizontal velocity gradients in the
near surface. I have modified this tomographic method so that the
objective funciton is no longer determined by tracing rays. The ray
tracing step is replaced by downward continuation in shot-geophone space,
resulting in an algorithm that is similar to the focusing depth analysis
method of Faye and Jeannot (1986). Rays are still used to back project
velocity corrections onto the model. I have not yet tried this new method
on real or synthetic data.
STANFORD