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Fig. 3.18 Open fissure in
thick calcite crust in Elata
Cave
Breaking of stalagmite with height of 237 cm can
be expected for mean +1r tensile failure stress at peak
ground acceleration in the range of 350-450 cm/s 2 .
Sampling and age determination were carried out.
A sample from 16 cm from the top of the stalagmite
was taken. The performed U/Th alpha spectrometric
measurement in ELTE University in Budapest shows
that the sample is not older than 6,000 years.
3.3.1.2 Razhishka Cave
The Razhishka Cave is situated in southwestern
Vratsa Mountain, West Stara Planina, NW Bulgaria.
The cave is located in the protected area of Lakatnik
Rocks on the left slope of the Stara Planina Iskar
River gorge. The big entrance at altitude of 460 m
and dimensions 7 9 6 m is clearly visible from the
Lakatnik railaway station.
The cave is developed in Triassic dark gray orga-
nogenic limestones from Babino Formation of the
Iskar Carbonate Group (Tronkov 1981 ). The age of
the formation is Anisian. Two major parallel reverse
fault structures with direction of 70 are identified in
the area (Tronkov 1965 ).
The Razhishka Cave has a length of 316 m and
denivelation of 32 m. The cave consists of single dry
Fig. 3.19 The investigated 237 cm high stalagmite in Elata
Cave with attached geophones
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