Geology Reference
In-Depth Information
(a)
(a)
(a)
-400
-350
-450
0
50 km
(b)
(b)
(b)
Fig. 6.24
(a) Observed Bouguer
anomalies (gu) over the Saguenay area,
Quebec, Canada. (b) The gravity field
continued upward to an elevation of
16 km. (After Duncan & Garland 1977.)
-400
application of
wavenumber filters
. Gravitational and mag-
netic fields may be processed and analysed in a similar
fashion to seismic data, replacing frequency by
wavenumber. Such processing is more complex than the
equivalent seismic filtering as potential field data are
generally arranged in two horizontal dimensions, that is,
contour maps, rather than a single dimension. However,
it is possible to devise two-dimensional filters for the se-
lective removal of high- or low-wavenumber compo-
nents from the observed anomalies.The consequence of
the application of such techniques is similar to upward or
downward continuation in that shallow structures are
mainly responsible for the high-wavenumber compo-
nents of anomalies and deep structures for the low
wavenumbers. However, it is not possible fully to isolate
local or regional anomalies by wavenumber filtering be-
cause the wavenumber spectra of deep and shallow
sources overlap.
Other manipulations of potential fields may be ac-
complished by the use of more complex filter operators
(e.g. Gunn 1975, Cooper 1997). Vertical or horizontal
derivatives of any order may be computed from the
observed field. Such computations are not widely
employed, but second horizontal derivative maps are
occasionally used for interpretation as they accentuate
anomalies associated with shallow bodies.
