Anisotropic velocity models
- The dimensions of the models were taken from the Marmousi model
and dataset (Versteeg & Grau, 1991).
- Each velocity model is composed of two homogeneous layers
separated by one curved interface. Velocity models differ by
the anisotropy of the upper layer. The bottom layer is isotropic in
all models and has P-wave velocity
Vp= 3.6 km/s.
- We also perform 3-D calculations in the model simply derived from the
2-D model by extension in the perpendicular direction.
- We compute recorded wave field
in models with isotropy and various types of anisotropy in
the upper layer:
a) Isotropic (ISO) upper layer with P-wave velocity
Vp= 2.5 km/s.
b) Transversely isotropic media with a horizontal
symmetry axis (HTI) representing a medium with aligned thin dry cracks
(Shearer & Chapman, 1989). The axis of symmetry
is parallel with the 2-D velocity model.
Anisotropy of P waves is 24% .
Reflected two-point rays are situated in the 2-D plane.
c) Triclinic anisotropy (TA) representing dry Vosges sandstone
(Mensch & Rasolofosaon, 1997). Reflected two-point rays propagate
in 3-D volume.
d) Monoclinic anisotropy (MA) . Reflected two-point rays
are situated in 2-D plane.
- We perform the migration
in homogeneous models (without curved interface) with anisotropy
specified in items a) - d) and also in the following
isotropic and anisotropic models:
e) Isotropic (ISO) models with P-wave velocities
Vp= 2.45 km/s
and
Vp= 4.5 km/s.
f) Transversely isotropic media with a horizontal
symmetry axis (HTI)
representing a medium with aligned thin water-filled cracks
(Shearer & Chapman, 1989).
The axis of symmetry is parallel with the 2-D velocity model.
Anisotropy of P waves is 15% .
Reflected two-point rays are situated in the 2-D plane.
g) Transversely isotropic media with a horizontal
symmetry axis (HTI)
representing again a medium with aligned thin water-filled cracks
(Shearer & Chapman, 1989).
The axis of symmetry is parallel with the 2-D velocity model.
Anisotropy of P waves is 3.5% .
Reflected two-point rays are situated in the 2-D plane.