Geoscience Reference
In-Depth Information
Fig. 2.4
Terminology for the
measured in situ tectonic
stress fields (following the
hierarchy proposed by
Bielenstein and Barron
1971
)
stresses (Fig.
2.4
) during the process of the evolution
of the karst systems are the main factor for creating of
fissures—tensional fractures or opening of the pre-
existing shear joints, in this way facilitating the water
circulation and formation of underground galleries
with dominant directions.
2.2.1
Striations on Tectonic
Slickensides
In these studies, the kinematic characteristics of the
movements between rock blocks are used. They could
appear at the moment of forming of joints and faults or
the orientation of older disruptions could favor the rel-
ative movement of adjacent blocks under the conditions
of younger tectonic stress field. The orientation of the
normal principal tectonic stresses could be recon-
structed through meso-structural analysis, using the
concept about the relation of movement along shear
joints with tectonic stresses (Ramsay
1980
; Gamond
1983
). The basic working hypothesis, called by the
name of Wallace-Both (Angelier
1994
) is that if there is
a movement and the system ''stress
()
fracturing'' is
examined independently of environment, then the rela-
tive displacement should be parallel to and along the
direction of the shearing stress. In Sect.
2.1
the basic
relationships have been presented (Griffith's Theory).
The critics of this hypothesis point out as its main
defect the fact that, due to the complicated real
geometry and the interrelation of faults and joints, a
considerable local deviation of the principal normal
stresses always appears. The practical analytical
results of a great number of conjugated disruption
surfaces with movements along them show (Angelier
1994
) that amazing constancy is kept and small angle
error in the orientation of the shearing stresses s. The
digital modeling (Dupin et al.
1983
—cited after
Angelier
1994
) has shown that the variances depend on
the geometry of the intercrossing of the joints, but these
variances are very small, within the limits of the error
2.2
Methods of Reconstruction
and Analyses of the Tectonic
Stress Fields
Among the methods for reconstruction of the spatial
direction of the axes of tectonic stress paleo-fields
these ones using the fracturing of the rocks in karst
areas have shown valuable results. The studies of the
striation on tectonic slickensides take a sizable place
in the information collected through the years of study
on different karst terrains. This type of reconstructions
corresponds to the meso-level of the description of the
structures, and where the kinematic characteristics of
the movements between the rock blocks are used.
Here only methods used in the practical works of the
authors for analyses of the tectonic stress fields in
relationship to the karst systems evolution will be
described and discussed.
Another possibility is the analysis of the physical
anisotropy when measuring in situ in karst terrains the
electrical or the seismic characteristics of the rocks.
The information about the contemporary regional
tectonic stress field can be also deduced on the base of
the
fault-plane
solutions
from
earthquakes
at
the
nearest vicinity of the studied karst terrains.
