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The spatial operator was designed to be gridcentered of eighth
order (9 points).
It can be decomposed in three parts for each component:
 
(10) 
where
 

 
 
 (11) 
and are antisymmetric but has no particular
symmetry (except in homogeneous media); and their form is represented
in Figure . The operators are gridcentered, normalized,
bidimensional difference stars.
spaceop
Figure 4 Spatial difference operators described by equation (11).
The temporal updating uses the operator described
in Cunha (1991) in this report. To obtain the wavefield and its
time derivative at time time only requires information
from time t, that is,
where the forward timepropagation operator has the form
 
(12) 
which represents a fourth order approximation in time.
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Stanford Exploration Project
12/18/1997