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in the development of different stages of typical step-
like karst within the boundaries of the study area have
been considered.
The post Upper Pleistocene deformations exam-
ined here, distinctly visible in the cave passages, can
be accepted as evidence in support of the thesis of
Tzankov and Nikolov (
1996
) about the occurrence of
a regional extensional tectonic stress field of NNE-
SSW orientation during the Neogene-Quaternary
structural stage in NW Bulgaria. The subhorizontal
extension environment is a precondition to the
observed type of faulting, i.e., prevalence of normal
and listric faults with their dip parallel to the stress
direction. The extensional stress field possibly influ-
enced the initiation of the Labirinta Cave configura-
tion and also controlled the main directions of the
cave passages in the surrounding part of the Zgorigrad
anticline—N-S
five big chambers (Fig.
3.31
). In the first two halls the
cave is developed along a sub-parallel fault line. The
total length of the galleries is 210 m and the deniv-
elation of the cave is 40 m.
During field studies conducted in the period
2000-2005 in Saeva Dupka Cave the following
indices of seismotectonic activity are described:
(A) Fallen stalagmites. In the cave were found 16
fallen stalagmites covered with thick calcite sedi-
ments. The overlay covering deformations are dry,
without recent dripping, suggesting the considerable
age of the deformations (Fig.
3.32
);
(B) Dislocated stalactone with diameter of 35 cm
(Fig.
3.33
). A displacement with an amplitude of
more than 40 cm in south direction is measured.
(C) Horizontal crack in a massive stalactone
(Fig.
3.34
). The stalactone has a diameter of more
than 3 m. Through the crack is observed a minimal
displacement in S-SE direction.
(D) Breakdown. The breakdown in Saeva Dupka
Cave is one of the biggest in the Bulgarian caves. The
fallen blocks cover an old generation of speleothems
that can be found in a few places. Some of the
boulders reach up to 3 m and are welded to each
other. In some cases they are covered with new spe-
leothems. Popov connected the brekadown occur-
rence and the formation of the eponymous chamber
(The Breakdown Chamber) as a result of catastrophic
paleoearthquake (Popov
1979
).
The built rose-diagram of the orientation of the
fallen stalagmites in the cave shows clearly the pre-
ferred direction to the south (Fig.
3.35
). The three
distinct peaks can be combined in common interval of
170-220 g. This fact can be interpreted as a result of
the activation of the fault south of the cave during the
Pleistocene. One may suppose that the formation of
the breakdown in the cave is supported by this phase
of intense tectonic activity.
In 2012, in Sueva Dupka Cave was installed TM-
71 extensometer in the frames of bilateral scientific
cooperation between the Czech and Bulgarian Acad-
emies of Sciences.
and
NW-SE
prevalently
(Kostov
1997
).
3.3.1.5 Saeva Dupka Cave
Saeva Dupka Cave is located in the Middle Fore-
Balkan, near village Brestnitsa, Lovech District. The
entrance is found on the south slope of the small
Bretsnishko polje with an area of 9 km
2
. The altitude
of the cave is 510 m. The entrance with dimensions of
4.2 9 4.5 m is opened at the base of a small rock
cliff.
The Saeva Dupka Cave is formed in the massive
light Titonian limestones of the Brestnitsa Formation.
The age of formation is Berriasian. The considerable
thickness of the limestones from Brestnitsa Forma-
tion, the low-angle slopes, and the high tectonic
fracturing are favorable conditions for intensive
karstification. The karst process is supported by faults,
expressed morphologically on the surface. One of
them is dipping to the north normal fault with parallel
direction, visible along the southern slopes of the
Brestnitsa polje, close to Saeva Dupka Cave. This
fault is marked with the presence of the impressive
abysses Big Ledenitsa Cave (-55 m), Small Leden-
itsa Cave (-40 m), and the pot-hole Partizanska Cave
(-107 m, with 98 m vertical pit).
The first data for Saeva Dupka Cave were pub-
lished at the end of the nineteenth century by Herman
and Karel Shkorpil in their monograph on the karst
waters in Bulgaria (Skorpil and Skorpil
1898
).
From a morphological point of view, Saeva Dupka
Cave consists of one large gallery, which separates
3.3.1.6 Troana Cave
The Troana Cave is situated in the central part of the
Belyakovo Plateau which is a morphographic unit of
the Central Fore-Balkan, North Bulgaria. The small
precipitate entrance is located about 3 km west from
the village of Emen. The cave is developed in highly
