Recent Applications of Turning-Ray Tomography And Tomostatics
By
Xianhuai Zhu1
(1) PGS Geophysical, 10550 Richmond Ave., Houston, TX
Turning-ray tomography and tomostatics have been applied to areas with
rugged topography and strongly variant near-surface geology. I review the
methodology of turning-ray tomography and tomostatics, and show how the
near-surface velocities estimated from turning-ray tomography are used for
static correction, wave-equation datuming and prestack depth migration.
Questions frequently asked will be highlighted to show 1) when and where
tomostatics will work better than conventional refraction
statics; 2)
limitations of tomostatics; and 3) key steps to run tomostatics. Quality
controls will be illustrated to ensure the robustness of turning-ray tomography
and tomostatics.
Turning-ray tomography and tomostatics enhance interpretation
and are
applicable to areas where
refraction
statics often fail, such as thrust belts,
high-velocity basalt or carbonate outcrops, unconsolidated low-velocity sand
dunes, marine trenches and shallow gas cloud regions. Although it does not
always provide better-stacked images than those from
refraction
statics,
tomostatics are at least as good as
refraction
statics. Interpreters often find
the near-surface velocity profile very useful when they determine a drill site.
Synthetic and field data
examples have shown that the resolution of
estimating a near-surface velocity model is directly dependent upon the picked
first arrivals. Picking the first arrivals via a virtual reality system
significantly improves the consistency of input
data
for the subsequent velocity
estimation.