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the movement direction. Correspondingly, the axis of
maximum compression is at 90 toward it.
2.2.1.3 Method of the Smallest Squares
This method complements the procedures for evalu-
ation of the spatial position of the principal axes of
stress field, and through it the final result of data
processing is formed. The reconstructed principal
axes of tectonic stress should be orthogonal toward
each other, but they might be dispersed around a
center, depending on the data. Exactly, through the
method of the smallest squares the position of this
center is determined for every principal axis observ-
ing the condition for spatial orthogonality between
them (Caputo and Caputo
1989
).
The main problem that arises at work with stria-
tions on slickensides is that the registered movements
along various surfaces, even very close (within one
outcrop), could not reflect synphase movements. If
within the rock volume there is a more than one
tectonic impact provoking movement along joints and
faults, it is obligatory during the field measurements
to find out or at least to suspect the relative temporary
sequence of the impacts. The accuracy of the final
result is depending from the number of the measured
surfaces with striations. It is represented by stereo-
gram (lower hemisphere) with results from RDM and
P/T methods (Fig.
2.6
).
Fig. 2.5
Measured parameters as input datum for the Pro-
gramme FAULT: dip direction, dip, pitch and sense of
movement (N—normal, I—reverse, D—dextral, S—sinistral)
of measuring, and practically the movement is always
parallel to the medium shearing stress. Thus, the
practical usage of Wallace-Both' hypothesis has been
confirmed. Numerous researchers created methods and
computer programs for reconstructions of tectonic
stress directions, using this very hypothesis (good
analyses and practical references could be found in
Sassi and Carey-Gailhardis
1987
; Vergely et al.
1987
).
The programme FAULT (Caputo
1989
) uses three
methods for reconstruction of the principal stress axes
by measurements of spatially oriented striations on
slickenside
and
the
types
of
movement
on
them
(Fig.
2.5
).
2.2.1.1 Right Dihedron Method
The RDM (after Angelier and Mechler
1977
) uses the
main hypothesis that the material is preliminary frac-
tured and the size of movement along every single
surface is much smaller than the size of the studied rock
body. The plane orthogonal to the striation on the
disruption surface is defined as a complementary plane.
Both planes divide the space around the disruption
surface into four rectangular dihedrons (sectors). Every
two conjugated dihedrons contain the axes r
1
and r
3
,
which could be presented into a stereographic projec-
tion. In a set of measurements, the sectors are defined
as zones of action of r
1
and r
3
axes.
2.2.2
Shear Joint Systems
The tectonic fracturing of the rocks gives valuable
information about the stress field that caused it and
about the orientation of dynamic axes, although it is
difficult to extract this information. In spite of the lack
of kinematic indicators on most of the joints, they
have great potential for reconstruction of the paleo-
stress fields. Especially, this can be used when the
joint sets keep consistent spatial orientation on wide
areas (Dunne and Hancock
1994
). Examples from a
platform region were presented and discussed by
Shanov (
2005
). Conjugated joint systems exist in all
cases of spatial orientation of the principal axes of
particular tectonic stress fields, which should be
studied for the reconstruction of the paleo-stresses. In
the most simple case, which is observed at pre-
liminary undeformed rocks (as the young sediments
are), there is a simple relation between the geometry
2.2.1.2 Method of Pressure (P) and Tension
(T) Axes (P/T)
It is based on the assumption that in homogeneous
and isotropic materials, the axis of maximum exten-
sion is under 45 toward the disruption surface and
