C. Macbeth et E. Liu, THE PROBLEM OF WATER-COLUMN MULTIPLES FOR PROCESSING CONVERTED S-WAVES IN MARINE VSP DATA, Geophysical journal international, 119(3), 1994, pp. 999-1004
Seismic data from marine VSPs contain converted S waves which can be u
sed to provide information on the internal structure of the subsurface
rocks. To make the best analysis of these waves it is necessary to ch
oose a suitable offset to maximize the converted energy. Numerical mod
elling with a hard sea-bottom shows that even for the moderate offsets
which provide the best conversions at the sea-bed in a shallow-water
environment, it is not possible to jointly compensate the P and S wave
s for their effective seismic signatures using a single common scalar
function. This is due to a difference in the periodicity of the water-
column multiples associated with the two wavetypes. The difference bec
omes more pronounced for a large Poisson's ratio in the sea-bed sedime
nts. Standard processing on the three-component recordings cannot be a
dequately performed except for subvertical incidence. Consequently, P
and S waves must be separated before signature deconvolution, or else
a more sophisticated multicomponent operator must be deployed. In the
process of acquisition design, the detailed modelling required to unde
rstand the multicomponent response must be weighed up against the offs
et desired for optimal conversion.