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Table 2.5
Reconstruction of the sequence of tectonic impact on the rocks of Iskrets-Gubesh Karst Region
Site
Late
Cimmerian
Sub-
Hercinian
Neotectonic
and recent
Origin
Pyrenean
Method
Earthquake
09.03.1980
M=4.4
N 42.95 0
E 23.35 0
Fault -
plane
solution
b
a
Shear
joints
b
a
M = 4.4 (Table 2.5 ) gives also reason to postulate
that the general orientation of the tectonic stress field
has been not changed drastically since the deforma-
tional processes during the Pyrenean Tectonic Phase
till now.
The orientation of the long axis of the electrical
anisotropy at N 5 for depths of about 30 m (AB/2
= 60 m) has not any response on the diagram of the
karst galleries (Table 2.5 ). But for Vratsa Karst
Region the same orientation was detected in the
Lower Cretaceous limestones and it was attributed to
the Sub-Hercinian Tectonic Phase (end of Turonian
time). In the studied area in the vicinity of Dushnika
Cave we can only suppose that this orientation is due
to the satellite fractures related to the well expressed
N-S striking Ejdan-Breze Fault, reflected also in the
morphology of the terrain as factor for the local N-S
orientation of the valley of Breze River.
The cause for interruption of the underground
water flow during strong seismic events is probably
related to tectonic deformation or rock collapses with
temporary formation of barrages inside the unknown
parts of the Cave Dushnika northward of the Iskrets
Karst Springs, especially in the area of Chernovodene
Fault (Fig. 2.38 ). The existence of unknown large
underground spaces has been proved by geophysical
studies to the north of the known parts of the cave
(Paskalev et al. 1992 ).
2.3.2.2 Central Balkan Area: Karlukovo
Karst Region
One of the most spectacular karst areas on the terri-
tory of Bulgaria is Karlukovo Karst Region (KAR). It
is located in the Central Balkan, in the morphological
structure named Central Fore Balkan (Fig. 2.29 ). It is
known especially for the cave with the spectacular
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