Geoscience Reference
In-Depth Information
Fig. 2.35
View of the lithostratigraphic sequence above the spring ''Jitoliub'', Milanovo Karst Basin (Bulgaria)
forms—62 % of the caves of Milanovo Karst Basin.
Most of the caves are not very long, but the largest
cave is the only active one in the area—Temnata
Dupka Cave with more than 5 km of galleries. This
cave is situated at about 40 m just above the spring of
''Jitoliub.'' The cave is a complicated labyrinth type
system with underground river running out its waters
trough the spring ''Jitoliub.'' The spring water is a
mixture between the underground flow from Pro-
boynitza River and the atmospheric precipitation
drained by Temnata Dupka Cave from the whole
catchment zone. Analyses show, that when the spring
discharge is low, the rate of feeding from Proboynitza
River
on Table
2.4
) have been analyzed. The second
methodology is based on the kinematics characteris-
tics of the movements on the rock block bounding
surfaces—striations on slickensides. Clear traces of
movements were found at the two sites (I and II,
Fig.
2.34
), and the analyses showed practically the
same solution for the tectonic stress field character-
istics.
The
summarized
solution
is
plotted
in
Table
2.4
(diagram II).
Electrical anisotropy studies were performed near
Sokolets Peak (site E2—Fig.
2.34
). The ellipses of
anisotropy were constructed using two arrays—AB/2
= 12.5 m and AB/2 = 80.0 m. The short array gives
information for the first 10 m, the long array—for a
depth of about 50 m below the surface. There is a
clear coincidence of the long axes of the electrical
anisotropy with the horizontal projections of the r
1
axes of the two reconstructed tectonic stress fields
(Table
2.4
, diagrams E2 a and E2 b). The limestones
are from the Triassic Carbonate Complex (T
2
) and as
a whole they are mostly affected by the Late Cim-
merian Tectonic Phase. The main tectonic faults of
the area
is
less
than
50 %,
and
it
decreases
with
increasing spring discharge.
Tectonic Stress Fields and Preferential Directions
of the Karst Galleries
Three methodologies were used for reconstruction of
the tectonic stress axes (Benderev et al.
2001
). The
first one is based on the analysis of conjugated shear
joints systems (Nikolaev
1977
) and the direction of
dispersion of their maximums. The measurements
performed at site I in Fig.
2.34
(IaandIbdiagrams
strike
NW-SE, likewise the axis
of
the
anisotropy for array AB/2 = 80.0 m.
