** Next:** The Trinidad data
** Up:** Alkhalifah & Rampton: Seismic
** Previous:** introduction

Alkhalifah and Tsvankin (1995) demonstrated that, for transversely
isotropic (TI) media
with a vertical symmetry
axis (VTI media), just two parameters are sufficient for
performing all time-related
processing, such as NMO correction (including nonhyperbolic moveout
correction, if necessary),
DMO correction, and prestack and poststack time migration. One of these two parameters,
, is a dimensionless parameter, whose departure from zero implies anisotropy,
and the other, , is the short-spread normal moveout (NMO) velocity
for horizontal reflectors.
These two
parameters
can be obtained solely from surface seismic *P*-wave data,
using estimates of stacking velocity for reflections from interfaces
having two distinct dips (Alkhalifah and Tsvankin, 1995). VTI media induce
nonhyperbolic
moveout of reflections that depends on and at
large
offsets.
Alkhalifah (1997) showed that these two parameters can be obtained by
analyzing the moveout at far offsets. The direct
output from such an
inversion (or velocity analysis) is the effective values of and ,
which include the combined (average) influence of the overburden. These
effective values are converted
to interval values using layer-stripping equations.
Interval estimates resulting from the inversion are a direct low-resolution
indicator of lithology, in which low values indicate sand-dominated
intervals, and
positive values indicate shale-dominated intervals.

** Next:** The Trinidad data
** Up:** Alkhalifah & Rampton: Seismic
** Previous:** introduction
Stanford Exploration Project

10/9/1997