4.
Interpretation of short wavelengths
So far we calculated short wavelengths of the gravitational effect from the TLUG geological model. It
appears quite useful to subtract them from the short wavelengths of the measured gravity prior to
their interpretation. After this procedure, several linear positive gravitational anomalies become much
more pronounced. These SE-NW oriented anomalies, which are absent in magnetic data, coincide with
the known fault zones. Malz and Kley (2012) referred to one of these fault zones as the two-phase
deformation, in which the compressional strain exceeded the preceding extensional deformation. This
leads to forming an anticline in shallow layers. Since these layers possess nearly zero magnetic
susceptibility, we observe the gravity anomalies which are not correlated with the magnetic ones.
Another type of anomalies is represented by two strong gravity anomalies noticeable also in magnetic
data. The linear anomaly is located in the central part of the Thuringian Basin, while the second
anomaly is arc-shaped and bounds the area of investigation in the north-west part. We used our
approach to interpret this type of anomalies on the mentioned linear anomaly in the central part of
the basin.
To verify if both gravity and magnetic anomalies are caused by the same object, we transformed
magnetic data to the pseudo-gravity and compared it with the measured gravity. For this purpose, we
applied our own algorithm. We assumed that the observed field is harmonic above some horizontal
plane
z = - h
located below the Earth’s surface. We exploited the representation of gravity as a solution
of the Dirichlet’s boundary-value problem for the half-space above the plane
z = - h
with given data
V
z
(x, y - h)
on the boundary and the Poisson’s equation which provides the following expression for
Fig. 4. Interpretation of the medium wavelengths. Left: depths to the density interface, obtained by inversion
after subtracting negative anomalies. Right: 3D model for the medium wavelengths. It includes density
interface with topography and 3 restricted bodies (intrusions) above it.
the vertical component
H
z
of the anomalous magnetic field intensity (Prutkin et al., 2012):
H
z
x',y',z'
=
∬
K
1
x',y',z',x,y
V
z
x,y,
−
h
dxdy
(2)
Using the known approximation for the total magnetic intensity anomaly
Δ
T
(Blakely, 1995), we
obtained a similar representation
ΔT
x',y',z'
=
∬
K
2
x',y',z',x,y
V
z
x,y,
−
h
dxdy
(3)
The expressions for the kernels
K
1
and
K
2
in Eqs. (2) and (3) can be found in Prutkin et al. (2012). We
treated Eqs. (2) and (3) as the linear integral equations of the 1
st
kind: the anomalous magnetic field
(its vertical component or the total magnetic intensity) is given at the Earth’s surface. Hence, we
solved the corresponding equation for the unknown downward-continued gravity
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