GEOLOGICA CARPATHICA, OCTOBER 2007, 58, 5, 487—493
www.geologicacarpathica.sk
Displacements registered around the 13 March 2006 Vrbové
earthquake M= 3.2 (Western Carpathians)
MILOŠ BRIESTENSKÝ
1
, JOSEF STEMBERK
1
and LUBOMÍR PETRO
2
1
Institute of Rock Structure and Mechanics, Academy of Sciences, V Holešovičkách 41, 182 09 Praha 8, Czech Republic;
milos.b.@post.sk; stemberk@irsm.cas.cz
2
Geological Survey of the Slovak Republic, Jesenského 8, 040 01 Košice, Slovak Republic
(Manuscript received October 10, 2006; accepted in revised form March 15, 2007)
Abstract: Information is given about the micro-displacement monitoring network in the Dobrá Voda epicentral area,
where regular monitoring started in May 2004 and an earthquake occurred on 13 March 2006. The measurement is
carried out with the use of verified, stable and sensitive 3D crack gauges TM71 produced by GESTRA Sedloňov,
Czech Republic. All the gauges installed across significant tectonic structures in this earthquake zone registered
displacements pertinent to the said last earthquake. The results obtained within the Dobrá Voda (W Slovakia) monitoring
network are analysed in view of the 13 March 2006 earthquake. The measurements indicated remaining sinistral
strike-slip displacements in the Dobrá Voda fault zone, as well as active subsidence of the Pannonian Basin. Moreover,
the measurements indicated even more detailed data about the fault movement development during the instability
process developing before and after the earthquake.
Key words: Dobrá Voda, micro-displacements, earthquake, TM71 crack gauge.
Introduction
The Dobrá Voda epicentral zone was selected to be inves-
tigated for displacements on several faults supposed to be
active according to geological studies. This area is one of
the most earthquake prone zones in Slovakia. The research
was initiated within the international project COST 625
“Monitoring of active tectonic structures”.
The first gauge was installed in Dobrá Voda village.
The area is known for the very significant Plavecké
Podhradie—Dobrá Voda fault, and measurements started
in May 2004. Three other gauges were installed in Octo-
ber 2005. The sites selected for the second installation
are also connected with important tectonic zones:
Smolenice fault, Plavecké Podhradie—Dobrá Voda fault
zone, and Ludinský (Dobrá Voda) fault zone (Figs. 1, 2,
3). The crack gauge TM71 was applied for this type of
monitoring, regarding its long successful use in many
countries. Let us name the Rhine Fault (Fecker et al.
1999), the Cordillera Blanca (Stemberk et al. 2003), the
region of Gargano and Norcia in Italy (Stemberk et al.
2003), a series of sites in Slovakia (Petro et al. 2005),
Simitli Graben in Bulgaria (Dobrev & Koš ák 2000;
Dobrev et al. 2005), the Gulf of Corinth in Greece, and
other places such as the Peter the Great Ridge in
Tajikistan (Koš ák et al. 1992).
On Monday 13
March 2006, at 8 h 28 min UTC, the vi-
cinity of the town of Vrbové was hit by a weak earthquake
(48.6
ºN, 17.7ºE). Its local magnitude was established as
M
L
= 3.2 (http://www.seismology.sk); according to the
ANSS catalogue, the hypocentre was situated at a depth of
10 km and magnitude established to M
L
= 3.6 (http://
www.ncedc.org/anss). The quake was felt in the surround-
ing area, and during the event damage to buildings was
registered too. This earthquake was the largest one during
the latest six years.
Dobrá Voda epicentral area – geological and
tectonic setting
The locality belongs to the northern part of the Malé
Karpaty Mts. It is a segment of the Inner Western
Carpathians. As far as neotectonic setting is concerned,
the area is situated in the Western Slovakia neotectonic re-
gion (Hók et al. 2000). The whole area is composed of
three tectonic structures: Mesozoic Brezová elevation,
Mesozoic Dechtice elevation, and Neogene strike-slip
Plavecké Podhradie—Dobrá Voda fault zone which forms
the northeastern part of the Mur-Münz-Leitha lineament.
The Plavecké Podhradie—Dobrá Voda fault zone origi-
nated during the Early Miocene (Marko et al. 1991).
Numerous earthquakes are produced here due to the
crossing of two fault systems: The Mur-Münz-Leitha
ENE—WSW striking lineament, and the Nesvačili-Trnava
NW—SE striking lineament. Generally, this region repre-
sents the most earthquake-prone region in Slovakia. The
strongest registered quake occurred on 9 January 1906,
with the intensity I
o
= 8.5
°MSK-64.
During the last century, 154 earthquakes of M > 2 were
registered here. The local microseismic network registered
1143 microearthquakes in the period 1999—2005. The
penultimate earthquake occurred on 19 September 2003
with magnitude M
L
= 3.1.
According to Marko et al. (Marko et al. 1991) the
present compressional stress field in the studied area is ori-
488
BRIESTENSKÝ, STEMBERK and PETRO
ented WNW—ESE. Grünthal & Stromayer (1986) state a
different direction: NNE—SSW.
Sites of TM71 devices
Dobrá Voda – Site No. I
Dobrá Voda site is situated at the SE contact of the Me-
sozoic Brezová elevation with the Dobrá Voda Depression
(Fig. 3). The depression is developed along NE—SW strik-
ing faults and forms a northeastern section of the Plavecké
Podhradie—Dobrá Voda fault zone (Fig. 2). Halouzka et al.
Fig. 2. Significant faults in Malé Karpaty Mts area (modified after:
Kováč et al. 1989; Marko et al. 1991; Hók et al. 2000) and sites of
the TM71 gauges. Black dots – TM71 sites, grey star – 13
th
March 2006 earthquake epicentre, TM71 gauges: I – Dobrá Voda,
II – Prekážka quarry, III – Slopy Cave, IV – Zbojnícka Cave.
(1999) supposed that the fault zone was active from
Middle Pleistocene to Holocene. It is typical of dextral
strike-slip slickenside (5
º 040º) occurrence. The gauge
TM71 was installed across a NE—SW striking fault cutting
Eggenburgian conglomerate (Fig. 4). It is located in a dis-
used railway furrow, near a local karst spring, in the vil-
lage centre.
Prekážka quarry – Site No. II
The gauge was installed across a NE—SW striking failure
(75
º 135º) cutting the Carpathian Jablonica conglomer-
ate (Fig. 5). It is a segment of the Smolenice fault (Fig. 2).
The fault was exposed in an old local quarry, in its west
facing wall. It is possible to find slickensides on a gravel
surface of normal fault character. Another system of slick-
ensides (34
º 225º) is not so significant, but has already
been discerned by Marko & Kováč (1996) as well. Accord-
ing to these authors, the fault represents a deep Badenian
normal fault. The fault forms a segment of the Malé
Karpaty Mts marginal fault zone, the fault border between
the northern part of the Malé Karpaty Mts and the
Pannonian Basin (Fig. 2). Its neotectonic activity was es-
tablished from the Late Pliocene to Quarternary (Halouzka
et al. 1999).
A gauge was installed in a trench, one meter below sur-
face.
Slopy Cave – Site No. III
The gauge was installed eight meters below the surface
in a karst – joint cave at Slopy Hill. The cave developed
in Wetterstein Limestones (Salaj et al. 1987), along a
NE—SW striking thrust fault (Figs. 3, 6). Development of
cave spaces was predestined by fault planes of 70
º dip,
downward changing to 55
º dip. According to Mitter
(1983), the cave is 75 m long and 30 m deep. Our analysis
proved 36 m depth, fresh damages of cave sintres, and
tectonic breccia. During winter seasons, warm vapour
arising on the surface has been observed.
Zbojnícka Cave – Site No. IV
The cave developed in Stainmal limestone (Salaj et al.
1987) of the Brezová elevation (Fig. 3) along an E—W fail-
ure. According to Mitter (1983) it is fluvio-karst type,
250 m long. A central gallery is cut by N—S striking faults,
and slickensides of normal fault character were found. The
gauge was installed at a depth of 11 m, across 65
º 245º
failure (Fig. 7) with dextral strike-slip horizontal compo-
nent. The component is documented by relative displace-
ment of blocks, and freshly crashed sinters as well (Fig. 8).
Methodology of monitoring
Long-term field measurement requires special equip-
ment, stable under hard outdoor conditions. Such a suit-
able instrument has been found in crack gauge TM71
Fig. 1. Position of the studied area.
489
DISPLACEMENTS REGISTERED AROUND THE VRBOVÉ EARTHQUAKE (WESTERN CARPATHIANS)
Fig. 4. Situation of Dobrá Voda site with TM71 gauge. 1 – anthro-
pogene sediment, 2 – faults, 3 – Eggenburgian conglomerate.
Fig. 3. Tectonic sketch of the Dobrá Voda epicentral
area and sites of the TM71 gauges (modified after:
Salaj et al. 1987; Marko et al. 1991). 1 – Pre-Senon-
ian lithostratigraphical units of the Inner Carpathians,
2 – Senonian and Paleogene of Myjavská pahorka-
tina Upland, 3 – Miocene, 4 – Quaternary
deluvial sediments, 5 – Quatenary fluvial sedi-
ments, 6 – faults, 7a – movements estimated
on the basis of structural analysis and monitoring,
7b – movements supposed by Marko et al. (1991),
8 – macroearthquake epicentres (1904—2003),
9 – TM71 gauges: I – Dobrá Voda, II – Prekážka
quarry, III – Slopy Cave, IV – Zbojnícka Cave.
Fig. 5. Prekážka qaurry site with significant faults (black arrows).
White arrow shows location of TM71 gauge.
(Fig. 7), produced by GESTRA, Sedloňov, a device tested
to suit such special demands (Koš ák 1991). This instru-
ment works on the mechanical optical principle (moiré),
with results showing any electrical transmission effect.
Due to its sturdy body and anticorrosion indicator ele-
ments, the equipment becomes very stable in nature, and
can survive under harsh long-term outdoor conditions, al-
most without any maintenance (Koš ák 2006). This gauge
proved able to survive current moderate seismic events,
while showing residual and permanent displacements. It
measures spatial displacement between two blocks or dis-
continuity faces.
The gauge system TM71 represents a combined moiré
3D displacement indicator equipped with 20 to 70 lines/
mm circular grids for displacement indication and 100
lines/mm linear grids to indicate angular deviation in
two planes (Koš ák 1991). In the case of minimum inter-
ference of exogene processes, the instrument is able to
demonstrate relative spatial movements between two
fault faces or two blocks, as low as 0.01 mm/year, and
relative angular deviations of up to 0.00032 rad. The
gauge TM71 bears Czechoslovak Patents Nos. 131631
and 246454.
In the case of the Dobrá Voda area, the measurements of
displacements are taken once per month.
Analyses and discussion of recorded displacements
An interesting fault mechanism in terms of block rota-
tion between boundary strike-slip faults was published by
Ron et al. (1984). Later Marko (1991) applied it to inter-
pret Middle Miocene deformations studied in the
Brezovské Karpaty Mts. Our observations at Dobrá Voda
together with other monitoring points reported here, come
to certain details in deformation trends that agree gener-
ally with such a mechanism but show a more complex de-
velopment connected with earthquake preparation period
490
BRIESTENSKÝ, STEMBERK and PETRO
and post-earthquake return to a relative stabilization. In
the following the observation will be demonstrated by key
graphs representing the results and will be interpreted with
regard to the specific observations that modify the above
theory.
Dobrá Voda – Site No. I
From the beginning of monitoring, during two years,
measurements were showing low dextral strike-slip dis-
placement trend (0.02 mm/year) along the fault combined
with sinistral block rotational trend (0.05 grad/year). Re-
garding such displacement observation as a phenomenon
preceding the quake event of 13 March 2006, the trend
Fig. 7. Vertical profile of the Zbojnícka Cave (documented: Briesten-
ský et al. 2006). 1 – cave walls, 2 – faults, 3 – TM71 gauge.
Fig. 6. Vertical profiles of the cave Slopy (documented: Briestenský et al. 2006). 1 – cave
spaces, 2 – TM71 gauge, 3 – tectonic breccia.
may be considered as induced by sinis-
tral strike-slip shear, along the main
fault of the Plavecké Podhradie—Dobrá
Voda fault zone (see Fig. 13A) that also
produce sinistral angular deviations at
the fault contact. It corresponds to
Marko et al. (1991), which assume that
this type of movement should be one of
the reasons for blocks rotation, active
during the Middle Miocene.
That clear trend sharply changed at
the time of the 13 March 2006 earth-
quake. This change is expressed as fast
relative counter micro-rotation of
blocks and as a relaxation effect along
the fault (see Fig. 9).
Registered angular deviations may
prove sinistral strike-slip displacements
along the main fault structures, which
exert the microblock system to sinistral
rotation with dextral strike-slip compo-
nent at their edges (Fig. 13A). After the
earthquake, microblocks are then al-
lowed to make opposite movements –
dextral rotation with a sinistral strike-slip component at
their edges (Fig. 13B).
Prekážka quarry – Site No. II
Generally, a linear trend of displacement was recorded
along the horizontal axis from the start of monitoring. The
value of displacement, corresponds to sinistral strike slip
movement, and reaches about 0.2 mm during about 1 year
of monitoring (y horizontal component). The vertical dis-
placement was calm until the end of January 2006 (z verti-
cal component). Then, a relatively fast acceleration of this
displacement was recorded. The value of vertical displace-
ment reached about 0.4 mm during about 1 month. Fi-
nally, the vertical displacement z, corresponding to
normal faulting, decelerated after 13 March 2006 event
(Fig. 10).
Recorded sinistral strike-slip faulting in this area is in
full agreement with geological and geophysical studies
(Procházková et al. 1986; Marko et al. 1991; Kováč et al.
2001). The sinistral strike-slip regime accompanied by re-
cent earthquake activity and fault-controlled subsidence
is documented at the southwestern edge of this fault zone
in the Vienna Basin (Hinsch & Decker 2003; Hinsch et al.
2005; Strauss et al. 2006). Strike-slip values monitored at
the Prekážka quarry site agree with the computed average
values of movement (0.01—0.1 mm/year) along the main
fault zones in the close vicinity during the Pliocene—Qua-
ternary period (Kováč et al. 2001) as well. It proves that
the movements continue today.
As for the acceleration of vertical displacement recorded
about one and half month before the earthquake, this
behaviour is discussed in medium-time earthquake predic-
tion theory, using the gauge TM71, and published by
Shanov (1993).
491
DISPLACEMENTS REGISTERED AROUND THE VRBOVÉ EARTHQUAKE (WESTERN CARPATHIANS)
Fig. 8. TM71 gauge installed across 65
º 245º failure in the Zboj-
nícka Cave. Fresh cracks brake sinters in the vicinity of the gauge.
Fig. 9. Block rotation at Dobrá Voda site. +gama xy – horiz-
ontal fault opening in SW direction (dextral strike-slip movement),
—gama xy – horizontal fault opening in NE direction (sinistral
strike-slip movement).
Fig. 10. Displacements observed at Prekážka quarry site. Y – strike-
slip displacements, Z – vertical displacements (subsidence of a SE
block).
Slopy Cave – Site No. III
Before the 13 March 2006 earthquake, during the initial
period, displacement measurements provided a dextral
strike-slip trend (0.1 mm/year) and the fault proved thrust-
ing movement in a SE direction. However, after the quake
event strain relaxation allowed for relative backward dis-
placement – relative normal faulting.
Such a development can be well demonstrated by the
development observed in angular deviation. Obviously,
the record (Fig. 11) displays an abrupt change from a
positive to a negative trend.
Yet, later, there appears a peculiar peak in the graph.
The peak found in August 2006 (Fig. 11) may raise ques-
tions as to what may have happened during that time. It
was just during the time of this peak that a swarm of ten
microearthquakes with M
max
= 2.2 occurred (according to
preliminary personal information from J. Sekereš –
PROGSEIS f.). The observation of the swarm passed dur-
ing 5—8 August 2006 and the swarm was located in the
close vicinity of the village of Trstín.
Zbojnícka Cave – Site No. IV
Initially, before the earthquake of 13 March 2006, we
observed a thrusting trend in a NE direction (Fig. 12),
which coresponds to sinistral strike-slip movements in the
Dobrá Voda—Plavecké Podhradie wide strike-slip fault
zone, as supposed by Strauss et al. (2006). This movement
trend stopped about one month before the event.
On the other hand the sinistral strike-slip displacements
began about one month before the event (Fig. 12). Both
observed displacement effects started before the earth-
quake and continue until now – September 2006.
The registered sinistral strike-slip displacements agree
generally with the results of Strauss et al. (2006) who
documented active subsidence in the nearby Pannonian
Fig. 11. Block rotation in Slopy Cave. + gama xz – vertical fault
opening in downward direction (thrust faulting), —gama xz – verti-
cal fault opening in upward direction (normal faulting).
492
BRIESTENSKÝ, STEMBERK and PETRO
Fig. 12. Block rotations in Zbojnícka Cave. —gama xy – horizontal
fault opening in E direction (sinistral strike-slip movements),
+gama xz – upward fault opening (thrust faulting).
Fig. 13. Model of actuotectonic regime in the Dobrá Voda area.
A – long-term regime, B – short before- and after-quake
regime, I – Dobrá Voda, II – Prekážka quarry, III – Slopy
Cave, IV – Zbojnícka Cave.
Basin, an effect accompanied by rare earthquakes. Thin-
skinned thrust types of deformations have been presup-
posed by Decker et al. (2005) along the Vienna Basin
Transform Fault (Mur-Münz-Leitha lineament) terminated
in the Carpathians.
Conclusions
Recorded data about displacements and rotations
around the 13 March 2006 Vrbové earthquake in the
Dobrá Voda epicentral area lead to following conclusions:
– displacements of the order of tenths of mm, as well as
angular deviations of up to 0.1 grad were registered in all
the gauges installed in the epicentral area during a broader
time period when the event occurred;
– specific displacements and angular deviations were
recorded not only after the 13 March 2006 quake event
but also before it;
– no displacements or angular deviations were ob-
served actually during the event as an immediate effect;
– displacements connected with the earthquake do not
need to appear generally at all observation points. The ob-
servations concern relative movements between structure
walls. Therefore, some points may not be affected because
both the opposite walls of the structure under observation
will move almost together and the local reaction will be
reduced;
– the 13 March 2006 earthquake seems to be a clear
breaking point of the behaviour registered in all the moni-
tored sites. That may be explained by strain release or a re-
laxation process after the earthquake in the epicentral area
(see Fig. 13);
– recorded trends of displacements and angular devia-
tions correspond generally to the geological findings re-
ported about the mechanism of recent tectonic movements
in the fault zones crossing the studied area;
– in spite of the positive reactions found in the records
the authors are aware of the fact that the monitoring period
before the event was a little short to confirm the effects
and correlations with geological findings unambiguously.
Nevertheless, the fact that all the monitoring sites show
confirmative reactions, increase their weight.
Aknowledgment: The authors express acknowledgement
for the financial support provided by the Czech Ministry
of Education, Youth and Physical Culture to the Project
COST OC 625.10, and by the Czech Science Foundation,
Project No. 205/05/2770.
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