Geoscience Reference
In-Depth Information
3.2.3
Monitoring of Recent
Geodynamics
In some caves are observed indicators of recent tectonic
movements on the elements of cave morphology. Such
indicators are dislocated passages in the cross section of
the gallery due to fault activity, tectonic mirrors,
presence of tectonic breccia, spatial discordance in the
couple ''stalactite—stalagmite reciprocal,'' and dislo-
cated or inclined stalactones (Figs.
3.8
and
3.9
). These
benchmarks for active tectonics in caves are described
in detail in the works of Wojcik and Zwolinski (
1959
),
Bögli (
1969
), Garasic (
1981
), Zacharov (
1984
), Gilli
(
1986
), Quinif (
1996
), Jeannin (
1990
), Bini et al.
(
1992
), Quinif (1997), Mochiutti (
2004
), and others.
The karstic caves are preferred as a medium for
geodynamic monitoring for two reasons: (1) In most
cases the tectonic deformations are fixed clearly
within the karst galleries and well preserved for a
relatively long period of time and (2) the cave's
annual temperatures are almost constant. Together
with the specific conditions of sedimentation in the
caves and the absence of dynamic geomorphic pro-
cesses such as excavation and weathering inherent to
the Earth's surface, the underground karst forms are
excellent places for installing extensometric facilities.
The robust conditions in most of the caves are a
precondition to usage of mechanical micro-tectonic
monitoring instruments. In several caves of Czech
Republic, Slovakia, Poland, Hungary, Slovenia, and
Bulgaria are installed mechano-optical extensometers,
named TM-71 (Briestensk
´
et al.
2010
; Gosar et al.
2011
; Kis et al.
2012
; Šebela et al.
2005
). The
instrument was developed by Prof. Blahoslav Kostak
from the Czechoslovak Academy of Sciences at the
end of the 1960s (Kostak
1969
) and was originally
designed for monitoring of fractures and cracks in
anthropogenic underground structures (tunnels, etc.).
The first TM-71 extensometer in a karstic cave was
installed in 1981 in Strochy pot-hole in Slovakia
(Briestensk
´
et al.
2010
). Recently, more than 160
gauges were mounted all over the world, including
Spitsbergen Island with its severe climatic conditions.
TM-71 works on the principle of the optical Moire
effect and needs no energy source. The microdis-
placements of cracks are recorded by two equal pairs
of optical glass plates. The precision of the dis-
placement recording of the device is ±0.007 mm in
X, Y, and Z coordinates (Klimes et al.
2012
). Detailed
Fig. 3.7
Sampling from the top of a 5.1 m high stalagmite in
Baradla Cave, Hungary (by Szeidovitz et al.
2005
)
formula for the acceleration amplitude of the breaking
is modified as follows: (Cadorin et al.
2001
)
rr
u
where q
2
a
g
¼
q
1
ð
T
=
T
0
Þ
Þ
2
þ
4q
2
ð
T
=
T
0
Þ
2
2qH
2
ð
log
2
e
1
;
9
þ
log
2
e
¼
ð
3
:
3
Þ
Knowing the quenching (g) (the value of (g) can be
calculated from the proportion of consecutive ampli-
tudes of seismograms made for the determination of
speleothem frequencies), D can be determined. T
0
is
the self-period of the studied stalagmite.
In the frames of bilateral scientific cooperation
between Bulgarian and Hungarian Academies of
Sciences, four caves in Bulgaria were studied in the
period 2005-2007. The results are presented in the
following subchapters of the topic.
Recently, this very perspective type of research
was continued by Dr. Katalin Gribovszki in caves in
Central Europe (Gribovszki et al.
2013a
,
b
,
c
).
