Gm. Hoversten et al., MARINE MAGNETOTELLURICS FOR PETROLEUM-EXPLORATION, PART II - NUMERICAL-ANALYSIS OF SUBSALT RESOLUTION, Geophysics, 63(3), 1998, pp. 826-840
In areas where seismic imaging of the base of salt structures is diffi
cult, seaborne electromagnetic techniques offer complementary as well
as independent structural information. Numerical models of 2-D and 3-D
salt structures demonstrate the capability of the marine magnetotellu
ric (MT) technique to map the base of the salt structures with an aver
age depth accuracy of better than 10%. The mapping of the base of the
salt with marine MT is virtually unaffected by internal variation with
in the salt. Three-dimensional anticlinal structures with a horizontal
aspect ratio greater than two can be interpreted adequately via two-d
imensional inversions. Marine MT can distinguish between salt structur
es which possess deep vertical roots and those which do not. One measu
re of the relative accuracy of MT acid seismic methods can be made by
considering the vertical and lateral position errors in the locations
of interfaces caused by neglecting velocity anisotropy in migration. F
or the shallow part of the section where two-way travel times are on t
he order of 1 s, the vertical and lateral position errors in the locat
ions of salt-sediment interfaces from 2-D MT inversion is more than tw
ice the expected migration error in reflectors in transversely isotrop
ic sediments, such as those in the Gulf of Mexico. Deeper in the secti
on where two-way times are on the order of 4 s, lateral position error
s in migration become comparable to those of the MT inverse, whereas s
eismic vertical position errors remain more than a factor of two small
er than MT errors. This analysis shows that structural mapping accurac
y would be improved using MT and seismic together.