Anisotropy for migration different
from the anisotropy for the recorded wave field
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We compare the triclinic anisotropy used for the recorded wave
field with the isotropy (ISO), transversely isotropic media with
a vertical and horizontal symmetry axis (VTI-1,2,3 and
HTI-1,2) used for the migration. These tests should simulate
situations when we have made a bad guess of the velocity model
for migration.
We shall divide results of our tests according to the values
of vertical and horizontal P-wave velocities.
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Vertical P-wave velocity in VTI-1 and HTI-1 models is the same
as analogous velocity in the triclinic (TA) model. Horizontal
P-wave velocity, parallel with the profile lines, in VTI-1 model
is nearly the same and in HTI-1 model the same as horizontal
P-wave velocity in the triclinic (TA) model. We optimized velocities
in models VTI-1 and HTI-1 for vertical and near vertical
rays to obtain the best results of migration.
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Migrated sections are very similar either we migrate in model
with VTI-1 or HTI-1 anisotropy.
Note the poorly displayed migrated interface in the horizontal
range approximately 4-6 km. The displaying of the discussed segment
of the interface (4-6 km) is worse for the model with the inclined
curved interface. The migrated interface is slightly mispositioned.
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Vertical P-wave velocity in the isotropic (ISO) and HTI-2 models
is the same as analogous velocity in the triclinic (TA) model.
Horizontal P-wave velocity, parallel with the profile lines,
in ISO and HTI-2 models is equal to vertical P-wave velocity
in the triclinic (TA) model. We optimized velocities also in models
ISO and HTI-2 for vertical and near vertical rays to obtain
the best results of migration.
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Migrated sections are very similar either we
migrate in model with isotropy (ISO) or HTI-2 anisotropy.
In this case the migrated interface in the horizontal
range approximately 4-6 km is displayed much better.
The segments of the interface in the horizontal ranges approximately
2-4 km and 6-8 km are defocused and mispositioned.
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Vertical P-wave velocity in the VTI-2 model is lower than vertical
P-wave velocity in the triclinic (TA) model. Migrated
interface is shifted vertically upwards (undermigrated) and is
slightly distorted. The vertical shift is smaller and the distortion
is greater for the model with inclined curved interface.
Migrated interface in the horizontal range approximately 4-6 km
is poorly displayed for the inclined curved interface,
analogously to the migration in the VTI-1 model.
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Horizontal P-wave velocity, parallel with the profile
lines, in the model VTI-3 is lower than horizontal P-wave velocity
in the triclinic (TA) model. In this case we can observe the poorly
displayed migrated interface in the horizontal range approximately
4-6 km. Compared with the migration in model VTI-1, the image of
the interface is slightly worse in the horizontal range of 4-6 km.