Phase-shift migration of passive seismic data
, by Steve Cole
Can passive seismic data be used to image subsurface structure? From
a processing standpoint, it seems possible. There is only one difference
between passive data and conventional reflection seismic data that will
require modification of existing wave-equation based imaging methods.
That difference is that in a passive survey, structures may be illuminated
by a variety of ambient noise sources over time, rather than a single
source whose position and excitation time are known. There is no "time
zero" at which our reflectors explode. This constraint is not difficult
to accommodate. In phase shift migration, for example, the downward
continuation step is unaffected; it is only the imaging step that requires
changes. I bypass the imaging step of phase shift migration and obtain a
picture of subsurface scatterer strength as a function of time. Intergrating
the power in this image over time gives an image of the subsurface. In
tests, this technique gives a consistent result when applied to passive data
recorded during different time intervals. While these results are preliminary,
their sucess suggests that imaging with passive data is a viable technique.
STANFORD