GeolCarp_Vol62_No4_381

www.geologicacarpathica.sk

GEOLOGICA CARPATHICA

, AUGUST 2011, 62, 4, 381—393 doi: 10.2478/v10096-011-0028-5

Introduction

The Horná Nitra Depression (HND) is situated in the western
part of the Central Western Carpathians. This depression is

Pliocene to Quaternary tectonics in the Horná Nitra

Depression (Western Carpathians)

RASTISLAV VOJTKO

, JURAJ BETÁK

, JOZEF HÓK

, FRANTIŠEK MARKO

, VOJTECH GAJDOŠ

KAMIL ROZIMANT

and ANDREJ MOJZEŠ

Department of Geology and Paleontology, Faculty of Natural Sciences, Comenius University, Mlynská dolina G, 842 15 Bratislava,

Slovak Republic; vojtko@fns.uniba.sk; hok@fns.uniba.sk; marko@fns.uniba.sk

Institute of Geography, Slovak Academy of Sciences, Štefánikova 49, 814 73 Bratislava, Slovak Republic

Department of Applied Geophysics, Faculty of Natural Sciences, Comenius University, Mlynská dolina G, 842 15 Bratislava,

Slovak Republic

(Manuscript received September 23, 2010; accepted in revised form March 17, 2011)

Abstract: The Horná Nitra Depression is an Upper Miocene—Quaternary intramontane sedimentary basin. This N—S elon-
gated half-graben structure is rimmed from the west by the marginal Malá Magura fault which is the most distinctive fault
in the Horná Nitra Depression, traditionally considered as an active fault during the neotectonic phase. This dislocation is
attended by contrasting landforms and their parameters. The low S-index of about 1.10, at least two generations of well-
preserved faceted slopes along this fault, and longitudinal river valley profiles point to the presence of a low-destructed
actual mountain front line, which is typical for the Quaternary active fault systems. Comparison with known normal fault
slip rates in the world makes it possible to set an approximate vertical slip rate between 0.3—1.1 m · kyr

—1

. The present-day

fault activity is considered to be normal, steeply dipping towards the east according to structural and geophysical data. The
NNW—SSE present-day tectonic maximum horizontal compressional stress S

and perpendicular minimum horizontal

compressional stress S

was estimated in the Horná Nitra region. The Quaternary activity of the Malá Magura fault is

characterized by irregular movement. Two stages of important tectonic activity along the fault were distinguished. The
first stage was dated to the Early Pleistocene. The second stage of tectonic activity can by dated to the Late Pleistocene and
Holocene. The Malá Magura fault is permeable for gases because the soil atmosphere above the ca. 150 meters wide fault
zone contains increased contents of methane and radon.

Key words: Western Carpathians, Malá Magura fault, neotectonics, morphotectonics, intramontane depression.

sidered to be the Sarmatian, after soft collision of the Alpine-
Carpathian-Pannonian (ALCAPA) block with the European
Platform (Pospíšil et al. 1992). This perspective was not very
successful because of diachronism of the collision front and

Fig. 1. Simplified digital terrain model map of the western part of Slovakia with location
of the study area shown by rectangle.

bounded by the Strážovské vrchy Mts on
the  west,  the  Žiar  Mts  on  the  north  and
east,  the  Tribeč  and  Vtáčnik  Mts  on  the
south  (Fig. 1).  The  HND  belongs  to  a
group of small, intramontane back-arc ba-
sins  in  the  Central  Western  Carpathians
(Kováč 2000). The depression has a poly-
genetic structure; sedimentary filling was
formed  mostly  in  continental  conditions
and  prevalence  of  fault  tectonics  pro-
duced  a  simple  block  of  asymmetrical
structure.  This  paper  focuses  on  neotec-
tonic  investigation  of  the  major  fault
structures. These faults were analysed by
the  methods  of  tectonic  geomorphology,
structural  geology,  remote  sensing  data
analysis, and geophysics.

In the Western Carpathians, the neotec-

tonics  (sensu  Stewart  &  Hancock  1994)
has been the subject of up to date studies
from  the  1980’s  to  the  present  day.  The
onset  of  neotectonic  processes  was  con-

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not  exact  timing  of  neotectonic  processes.  The  evolution  of
the ALCAPA area and current position of its tectonic units is
considered to be connected with collision of the Eastern Alps
and  Bohemian  Massif  and  the  lateral  escape  of  crustal  frag-
ments from the collision zone (e.g. Ratschbacher et al. 1991;
Kováč 2000). These tectonic processes were accompanied by
compression and the evolution of diachronous nappe systems
at the front of the orogen (Jiříček 1979; Kováč 2000), segment
rotation  (Csontos  1995),  transpressional,  transtensional,  and
extensional tectonic regimes during the Neogene (Fodor 1995;
Kováč & Baráth 1996; Fodor et al. 1999; Pešková et al. 2009;
Vojtko et al. 2010), and volcanic activity of the back-arc type
(e.g. Lexa et al. 1993; Lexa & Konečný 1998). The basic neo-
tectonic research was finalized in the neotectonic map of Slo-
vakia (Maglay et al. 1999; Hók et al. 2000).

In the tectonic evolution of the ALCAPA region, it is pos-

sible to distinguish several tectono-sedimentary megacycles,
from  which  the  last  cycle  started  at  the  Miocene/Pliocene
boundary (Kováč & Baráth 1996; Kováč et al. 1997). At the
same  time  the  tectonic  regime  changed  to  extensional  and
continued up to recent times (Bada 1999). From the point of
view of Quaternary geology of the Western Carpathians and
Pannonian Basin (Baňacký et al. 1993; Maglay et al. 1993),
the neotectonic processes are younger than in previous defi-
nition and include tectonic events which have occurred from
the  Pliocene/Pleistocene  boundary  (2.558 Ma;  Gradstein  et
al. 2004) up to recent. However, the Pliocene dynamics was
important for the Quaternary evolution (Vojtko et al. 2008).

Finally, we define the term ‘neotectonics’ for the Western

Carpathian area as tectonic events and processes which oc-
curred during the Pliocene and Quaternary; from 5.4 Ma to
the present-day (Hók et al. 2000; Vojtko et al. 2008). In this
paper we present a multidisciplinary approach for neotecton-
ic research.

The aim of the paper is to test and verify the neotectonic

activity along the Malá Magura fault zone in the HND using
the methods of structural, paleostress, geomorphological and
remote sensing data analysis, and geophysical profiling,
which are comprehensively presented in chapter “Methods
of neotectonic investigation”.

Geological setting

The pre-Cenozoic basement of the HND is composed of the

Late  Paleozoic  basement  and  the  Mesozoic  cover  sequences
which  belong  to  the  Tatric  Unit.  The  nappe  structure  of  the
Fatric  and  Hronic  Mesozoic  Units  is  superimposed  over  the
Tatric Unit (e.g. Mahe  1985). They form elevated structures
of  the  Žiar,  Strážovské  vrchy  and  Tribeč  Mts  and  submerge
below  the  Paleogene  and  Neogene  volcano-sedimentary  de-
posits of the HND (Fig. 2).

The lowermost part of the sedimentary fill of the HND con-

sists of a Paleogene sedimentary succession, which represents
a mixed facies of the Central Carpathian Paleogene and the
Buda Basins provenance (Gross et al. 1970).

This sedimentary succession is discordantly covered by

the Neogene deposits, which contain intercalations of prod-
ucts of Neogene volcanism. The Neogene sediments were

deposited  during  two  main  sedimentary  megacycles.  The
older  megacycle  is  represented  by  Eggenburgian  marine
deposition. During the Middle and partly Late Miocene sec-
ond  sedimentary  megacycle,  typical  basin  and  range  struc-
tures (Nemčok & Lexa 1990) were formed. Volcanic activity
was located predominantly in the south-eastern part (Vtáčnik
Mts).  The  Lelovce  Formation  (Pontian  to  Pliocene)  repre-
sents  the  youngest  Neogene  sediments  (gravels,  sands,  and
clays) of the HND which cover denuded relief and represent
an infill of paleovalleys.

The Pleistocene sediments belong to the highest parts of

the HND sedimentary fill. They are deposited at the foothills
of the Strážovské vrchy Mts as huge alluvial fans. The rem-
nants of the Lower Pleistocene terraces are located 120—150
and  90—110  meters  above  the  Nitra  River  floodplain.  The
Middle  Pleistocene  sediments  are  spread  out  in  the  morpho-
logically lower positions and they are developed in 3—4 levels,
alternately  on  the  right  and  left  side  of  the  Nitra  River.  The
sedimentary  bodies  of  the  Middle  Pleistocene  are  situated  at
the levels 45—90 and 20—40 meters above the Nitra floodplain.
The Upper Pleistocene sediments consist of two typical accu-
mulations of sandy gravels. The youngest morphological level
(approximately 3—16 meters above the Nitra River) is formed
by the flat lying Würmian alluvial fans. The maximum thick-
ness  of  the  fans  varies  from  4  to  10  meters  (Šimon  et  al.
1997a,b).  The  Holocene  was  mainly  characterized  by  fluvial
deposition  along  the  rivers.  The  thickness  of  fluvial  deposits
of the Nitra River is generally 2—5.5 meters.

The Pleistocene and Holocene travertines were formed

along activated faults (Šimon et al. 1997a,b; Kernátsová in
Gajdoš et al. 2005). Holocene travertines are predominantly
situated near Bojnice Spa and form individual mounds which
often cover Pleistocene travertine (Fig. 2).

Methods of neotectonic investigation

Neotectonic activity of faults was tested by various meth-

ods of structural geology, geophysics, and morphotectonics
supplemented with remote sensing data interpretation. The
most eligible used methods, which were partly modified, are
described below.

Investigation was focused on testing neotectonic activity

of regionally important faults. The most important structure
in the area is the Malá Magura fault, which was analysed in
detail and the results are presented here. The same methods
of research were also used for other important faults affect-
ing the basin such as the Pravno, Šútovce, Hájske, Necpaly
and Brezany faults.

Structural and paleostress analysis

Structural research was focused on brittle structures related

to the Neogene—Quaternary paleostress field, including travi-
tonics (sensu Hancock et al. 1999). It included field structural
research, which involved measurement and collection of field
structural data, kinematic analysis of slickensides and process-
ing of structural data including orientation and paleostress
analysis. Combination of field meso-scale observations with

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Fig. 2. Simplified geological map of the Horná Nitra Depression with main fault structures (according to Šimon et al. 1997a, modified).
Note: thick red lines indicate position of geophysical profiles.

map-scale structures analysis has been applied. It has been ac-
cepted,  that  small-scale  structures  can  be  related  to  large  re-
gional  structures  and  that  both  scales  reflect  the  same
dynamics  and  kinematics  (Angelier  1994).  The  inversion
method based on the Wallace (1951) and Bott (1959) assump-
tion that the slip on a plane occurs in the direction of the maxi-
mum resolved shear stress was used for paleostress analysis.

Geomorphological analysis

According to Urbánek (1999), geomorphological analysis is

a method covering a wide range of particular steps. In the first
step, the identification of the tectonically-controlled land-
forms was done. The topographic data, precise Digital Terrain

Model (DTM), other DTM-derived data and satellite imagery
data  were  used  during  the  identification  process.  The  DTM
used  in  this  study  was  derived  from  vectorized  contours  of
1 : 10,000  topographic  maps  with  cell  size  of  5 m  in  the
S-JTSK  (Datum  of  Uniform  Trigonometric  Cadastral  Net-
work)  coordinate  system.  Longitudinal  valley  profiles  were
constructed on vectorized contours at a scale of 1 : 10,000.

Morphotectonic pattern

Many models describe the specific landforms of tectonically

active relief, their spatial distribution, possible origin and fur-
ther evolution (Thornbury 1956; Costa & Fleisher 1984;

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Stewart & Hancock 1994; Burbank & Anderson 2001; Minár
2003).  The  spatial  distribution  of  the  identified  landforms
helps  us  to  identify  important  features:  lineaments  and  mor-
photectonic  pattern.  Particular  lines  may  be  categorized  ac-
cording to their sums of segment lengths and the robustness of
the  landforms,  which  are  cut  or  limited  by  a  line.  It  appears
that analyses of DTM underlain with shaded relief (illuminat-
ed from different azimuths) are very suitable tools for identifi-
cation  of  the  morphotectonic  pattern.  On  the  other  hand,  the
important geomorphic markers are preserved sometimes in re-
lief details. The morphotectonic pattern can help to reveal or
append  some  important  information  about  the  complex  re-
gional fault system. The following step identification, spatial
distribution  and  characteristics  of  facets,  denudational  rem-
nants of flat surfaces, and their interrelationships were crucial
points in geomorphological analysis.

Linearity of mountain front

The linearity of the mountain front was quantified by the

slightly reinterpreted S-index, introduced by Bull & McFadden
(1977) using the formula:

S = L

where L

is the total length of the considered segment of the

mountain front, and L

is the length of abscissa, which con-

nects the end points of the considered segment of the moun-
tain front. The L

value should reflect the real course of the

fault system, on which the mountain front was developed.

The S-values close to 1 indicate the mountain front predis-

position  by  young  tectonic  processes.  The  higher  resulting
value  indicates  the  degraded  mountain  front,  which  implies
possible  tectonic  inactivity  (interconnected  with  weathering
conditions) or extremely fast weathering processes. However,
the  authors  of  the  S-index  were  considering  especially  the
straight  mountain  fronts.  In  the  Western  Carpathians,  tilted
and rotated blocks of various volumes are common. This pro-
duces  complex  fault  systems,  not  only  straight  but  often
curved patterns. In this case the use of the L

value in the tradi-

tional way might produce faulty results. Therefore, we experi-
mented with tuning the L

value. The considered mountain

front has rather the shape of the 2

quadrant of the ellipse

elongated according to the Y axis. The length of this segment
was used to evaluate the value of S.

Thirdly, it is likely, that the fault system limit well-pre-

served facets and underlying flat base surfaces. Therefore in
this case, the idealized mountain front defined by the flow-line
which delimits the lower facets’ L edges was used.

Geomorphological profiling

Profiling is still one of the important tools of tectonic geo-

morphology. The profile ridge lines usually preserve the most
of the significant landforms on the slopes. If some remnants of
the  planated  or  structural  surface  are  presented,  their  occur-
rence  is  often  preserved  on  ridges.  They  preserve  the  oldest
micro- and meso-forms on the local slope, while the forms in-
side are usually denuded by later slope degradation (e.g. slid-
ing  and  young  valley  propagation).  The  longitudinal  profiles

of valley floors belong to the second important group. There
are plenty of methods, which help us to requantify the length
and  height  values  (e.g.  computation  of  equilibrium,  profiles,
and various indices). However, our experience shows that, be-
cause  of  data  quality,  in  the  large-scale  morphotectonic  re-
search  the  visual  analysis  and  expert  intervention  of  each
particular profile plays the most important role.

Another method of evaluating longitudinal profiles is the

analysis of K-index diagrams, which show the rate of con-
cavity of the valley profile (Zuchiewicz 1980, 1995) using
the formula:

= K-strech/H

where K-stretch is the longest perpendicular distance from the
triangle’s hypotenuse, H

is the length of the height of the tri-

angle, whose hypotenuse is the diameter of the triangle.

The K-stretch might be measured on a graph, the mathe-

matical  computation  of  which  was  introduced  by  Novotný
(2006).  According  to  Zuchiewicz  (1980),  the  rate  of  valley
concavity  grows  with  the  lowering  of  the  vertical  tectonic
activity.  The  position  of  K-stretch  divides  the  valley  with
prevailing  bottom  erosion  in  the  upper  part  and  prevailing
lateral erosion in the lower part.

Geophysical methods

Geophysics was used for testing and characterization of

fault  zones  on  the  basis  of  physical  behaviour.  Electrical
methods  [vertical  electric  sounding  (VES),  low  frequency
method  (dipole  electromagnetic  profiling  (DEMP),  very  low
frequency  (VLF)),  spontaneous  polarization  (SP)  and  pulse
electromagnetic  emission  (PEE)],  soil  radon  and  methane
measurement were used to obtain this information.

Results and interpretation of neotectonic

investigation

Upper Neogene to Quaternary stress field evolution

In the northern part of the HND, only a few outcrops were

suitable  for  structural  analysis  because  unconsolidated
Quaternary  alluvial  fans  almost  completely  cover  older
strata. Fault-slip analysis was also carried out at outcrops in
the neighbouring Bánovce and Turiec Depressions. For the
young  tectonic  evolution  of  the  HND  relief  and  adjacent
mountains,  the  Late  Miocene  to  Holocene  tectonic  regimes
and deformation  played the crucial  role. This  young tectonic
evolution  was  controlled  by  three  deformational  subphases
characterized  by  the  NW—SE  compression,  NNW—SSE  ex-
tension,  and  WSW—ENE  extension.  Compression  oriented
NW—SE is considered to be Late Miocene (Late Pannonian to
Pontian) in age because it is younger than the NE—SW compres-
sion  prevailing  in  the  Upper  Sarmatian  to  Lower  Pannonian
strata (Hók et al. 1995). These compressional tectonic regimes
were followed by normal faulting during the neotectonic phase.
The extensional tectonic regime with the NW-SE-oriented prin-
cipal  axis

played an essential role during the Pliocene

(Vojtko et al. 2008; Králiková et al. 2010). The NE—SW tension

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Fig. 3. Rose tectonogram of joints measured in the Bojnice Spa travertine mounds. Note: azimuth
interval 26°, maximum of azimuth data (39 %); interval of dip 10°, maximum of dip data (56 %).

Fig. 4. Morphotectonic pattern in the studied area.

is the youngest deformation event de-
scribed from the HND and Nitrianska
pahorkatina  Lowland.  This  deforma-
tion  phase  was  precisely  dated  to  the
Late  Pliocene  to  Holocene  timespan
(Vojtko et al. 2008).

Near the town of Bojnice, defor-

mation  of  travertine  mounds  was
also  studied  but  no  fault  slip  data
were  obtained.  However,  a  system-
atic  joint  pattern  (37  joints)  was
identified  and  it  indicates  that  the
travertine mounds were deformed in
the condition of the NE—SW orient-
ed tension in general (Fig. 3). Unfor-
tunately, using the obtained data, we
were  not  able  to  responsibly  deter-
mine a tectonic regime.

Geomorphological analysis

Geomorphological parameters

The lineaments, depicted as the

boundaries or interconnections of the
landforms  control  the  morphotecton-
ic  pattern  of  the  study  area  (Fig. 4).
The lines are subdivided into four hi-
erarchical orders (from continuous to
dotted lines) reflecting the robustness
and  properties  of  the  potentially  tec-
tonic  landforms,  which  delimit  the
particular line and length of the linea-
ment in the specified direction.

The resulting morphotectonic pat-

tern is complicated as well as the tec-
tonic preconditions of the study area.
It  is  possible  to  distinguish  a  few  in-
ner  sub-patterns.  The  most  sensible
are the lines, which divide the moun-
tain  ranges  and  the  basin.  Their
course  is  obvious  on  satellite  images
in visible and infrared as well as radar
wavelength  spectrum.  In  most  cases
they  copy  the  identified  mountain
fronts. They delimit contrasting forms
(such  as  faceted  slope  and  flat  sur-
face),  interconnected  along  the  same
line  (alternatively  the  same  system
composed  of  more  particular  lines).
Within the broader view of the study
area,  three  such  systems  were  identi-
fied.  Two  of  them  have  the  NW—SE
direction  (SW  delimitation  of  the
Strážovské  vrchy  Mts  and  the  HND;
the  SW  delimitation  of  the  Žiar  Mts

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and the HND). Both of them have a rather linear shape. The
third system is a non-linear delimitation of the SE part of the
Strážovské vrchy Mts and the HND. In general, this is the N-S
striking system, which in its northern part slightly turns to the
north-east (Malá Magura fault).

The northern margin of the focused area is quite complicat-

ed. A few parallel ENE—WSW lines, which in the WSW part
run further into the Strážovské vrchy Mts and delimit its core
massif in the north, were identified. The morphotectonic pat-
tern within the Žiar Mts is rather regular, mostly formed by the
NW—SE lines (parallel to its mountain front) and NE—SW
cross-lines (Fig. 4).

The landforms in the basinal area are usually less robust

than the morphostructures in the mountain area and connec-
tions with potential tectonic activity are usually less preserved
in the landforms. Therefore, the lines have lower tectonic sig-
nificance. However, the spatial distribution of the identified
landforms in the basinal area reveals the possible block struc-
ture. Most of the lines in the eastern and northern parts of the
basin are the continuation of particular lines in the mountain-

ous area. The morphotectonic pattern in the western (the core
of study area) part is hard to build just from relief features and
it is quite unique (Fig. 4). We will pay attention to this in a
more detailed analysis.

Mountain front sinusoity (S-index)

The Malá Magura fault occurs in the context of the mor-

photectonic pattern. In the relief, it is represented especially
by contrasting landforms (faceted slopes vs. flat surfaces),
which can also be associated with the eastern mountain front
of the Strážovské vrchy Mts (Fig. 5). The S-index, according
to the computation introduced by Bull & McFadden (1977),
reaches the value of 1.17 within the study area (Fig. 6). This is
not far from value 1.0, which expresses the identity with the
non-destructed mountain front line. However, our experimen-
tal method gives even lower values (S

ideal

= 1.09; S

ellipse

= 1.10;

for further information see Fig. 6). These low values indicate
tectonic processes, which often create such linear features in
the relief. We take into consideration, that weathering pro-

Fig. 5. Slope angle map of the Horná Nitra Depression and adjacent mountains. The grey colour indi-
cates inclination of slopes in degrees. Solid lines represent faults.

cesses in the neotectonic peri-
od in the Western Carpathians
were highly active, in general.
The  fact,  that  the  mountain
front is not very destructed by
exogenic  processes  yet,  sup-
ports  the  hypothesis  about
Quaternary  tectonics,  which
have  played  a  considerable
role  in  the  shaping  of  such
contrasting landforms.

Mountain front faceting

Along the entire mountain

front  we  can  distinguish  three
groups of landforms. The first
are  the  faceted  slopes  situated
to the west of the studied fault
system; flat surfaces are situat-
ed  to  the  east.  Both  groups  of
landforms fringe the mountain
front  on  either  side.  The  third
group  includes  the  valleys,
which  cross  and  disintegrate
this system of landforms.

The system of facets fring-

ing the studied fault system is
composed  of  more  sub-
systems  (Fig. 7).  The  Mali-
novský  stream  divides  the
facets  into  two  groups.  The
southern group contains com-
posite  facets.  The  younger
generation  is  situated  above
the mountain front line. These
facets are still well-preserved,
gradually  dissected  by  incipi-
ent  headward  erosion  of  re-

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fied. However, there are some geomorphic markers which
indicate also the older generation, but this system is in a
higher stage of degradation.

The front facets are the most interesting landforms for ac-

tive tectonic assessment. (Fig. 7). A few dependencies were
noticed. First of all, robustness and the vertical range gradual-
ly increase from the south to the north. The southern facets
achieve relative heights below 200 m, the northern rise up to
400 m. In the scale of long-term development, this feature is
typical of the scissor-like effect in the normal fault system.

Secondly, a few remnants of flattened surfaces were identi-

fied  inside  the  facets.  Some  of  them  are  situated  randomly
(which  can  be  caused,  for  example,  by  deep-seated  block
creeping), others, however, relate among each other on the ba-
sis  of  average  altitude.  Their  absolute  altitudes  vary  from
500 m a.s.l. in the south up to 630 m a.s.l. in the northern part
on all studied facets (in case of facets 1 and 2 these flattened
surfaces create the tops of the facets). Expressing this in rela-
tive  values,  the  flattened  surfaces  occur  at  120—150 m  above
the mountain front line, which clearly appears in the plots of
selected ridge profiles (Fig. 7). This indicates that the vertical
effect of tectonic process on the Malá Magura fault could have
been  interrupted  and  for  a  short  time  the  passive  processes
took over the dominant role in the relief shaping and built the
pediment. However, this stage did not last for a long time, be-
cause  the  pediment  spread  only  very  locally,  presently  wit-
nessed by the analysed denudational remnants.

Fig. 6. Three alternatives of the S-index calculation.

Fig. 7. Facet levels and selected ridge profiles.

cently seated valleys. They are incorporated into a larger sys-
tem,  whose  facets  are  strongly  degraded  by  long-term  bot-
tom  valley  erosion.  The  remnants  of  their  genuine  shape
have been only identified. The existence of composite facets
points  to  multi-stage  tectonic  development  of  the  studied
slope.  In  the  northern  group,  only  front  facets  were  identi-

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The inclination of the faceted slopes computed on topo-

graphic data reflects the trend of inclination of the facets and
ignores the meso- and micro-forms on the slope. The compu-
tation of the average value of inclination on DTM produces
rather higher values, while it also involves the detailed mod-
elling,  such  as  small  valleys  with  steep  slopes.  The  differ-
ence between these two values is evident especially in case
of facets 3, 7, and 8, which are at the same time the most dis-
sected  ones  from  the  group  of  studied  facets.  The  facets 5
and 6 are less dissected, the smallest ones (facets 1 and 2) re-
flect  only  the  initial  stages  of  the  slope  erosion  (Fig. 7).
Compared to other faceted slopes in the surrounding moun-
tain  ranges  of  the  HND,  the  facets  above  the  Malá  Magura
fault are almost “fresh”.

Characteristics of alluvial fans

An interesting mosaic of landforms is found on the oppo-

site site of the faceted slopes, in the basinal part of the study
area.  Plenty  of  alluvial  fans  of  different  volume,  shape  and
age were described. East of the mountain front line (in rela-
tion  to  sudden  change  of  slope  inclination),  the  numerous
small Upper Pleistocene to Holocene alluvial fans or in some
cases  debris  flow  accumulations  were  identified  (Fig. 2).
They  are  composed  of  sandy-gravel  material,  redeposited
from small valleys cut into the faceted slopes on the eastern
flank of the Malá Magura Mts.

The medium size streams cut through their own Lower and

Middle  Pleistocene  depositions,  transport  the  material  and
develop  their  alluvial  fans  in  the  central  basin.  The  largest
volumes  of  transported  and  deposited  sediments  naturally
occur  around  the  dominant  streams,  which  have  developed
catchments  also  inside  the  mountain  range  (the  alluvial  fan
of Poruba, Chvojnica, and Tužina streams). In general, all al-
luvial  fans  occur  on  the  eastern  side  of  the  mountain  front
line (toward the basin), which supports the assumption of the
recent activity of the Malá Magura fault.

In the case of the Chvojnica valley, the Upper Pleistocene

to Holocene alluvial fans cap the older sediments just on the
contact  of  the  mountain  and  basin  zone  (Fig. 2).  This  is
known as alluvial fan superposition and clearly points to tec-
tonic  uplift  of  the  mountains  or  tectonic  subsidence  of  the
catchment.  However,  the  probable  interpretation  of  forma-
tion of the Upper Pleistocene to Holocene Chvojnica stream
alluvial  fan  could  be  rooted  in  a  more  complex  process  in-
volving deep-seated block creeping and massive landsliding.
This is indicated by three translated and rotated blocks (ap-
proximately  0.5 km

each) localized on the left bank of the

present Chvojnica stream. On the right bank forms of recent
landsliding are evident. Active tectonics often influences
such a pattern of landforms.

Longitudinal valley profiles

Information about tectonic activity of the mountain front

system is also found in the longitudinal profiles of selected
valleys (Fig. 8). Unlike the young valleys embedded into facets
with simple concave longitudinal profile (cases 2, 3), the de-
veloped valleys have more complex longitudinal profiles.

They are composed of two dominant parts: the upper part with
a concave profile and the lower part with an almost linear (e.g.
cases 1, 4, 5, and 8) or even slightly convex longitudinal pro-
file (case 9). The two levels of longitudinal profiles do not re-
flect  their  equilibrium.  The  knickpoints  occur  around  the
absolute  elevations  between  400—500 m a.s.l.,  which  is  the
space  where  the  mountain  front  line  fluctuates.  The  regimes
beneath  and  above  these  points  are  different.  The  linear  (or
even convex) profile lines indicate that the potential uplift of
Strážovské vrchy Mts has been faster than headward erosion
of the streams. The valley gradient in the basin area is in some
cases higher than the gradient in the lower mountain part. The
convex  bending  of  the  largest  Tužina  stream  also  indicates
possible subsidence of the central part of the basin (Fig. 8).

Geophysical measurements

Geophysical methods have been used to test the neotectonic

activity of the Malá Magura fault (VES, SP, VLF, PEE and
some  others).  The  measurements  were  carried  out  on  two
profiles  perpendicular  to  the  faults  system.  These  profiles
(near  Malinová  and  Opatovce  villages)  were  located  on  the
Malá Magura fault (Fig. 2).

Malinová geophysical profile

Geophysical measurements by VES, SP, VLF, PEE, magne-

tometry, radon and methane content measurements in soil air
were carried out on this profile (Fig. 9). The results of the VES
measurements indicate that the Malá Magura fault is a normal
one  with  a  faulted  zone  about  120  meters  wide.  In  this  zone
the radon emanation has a higher content and changeable rate
in the mountain part of the profile that is consonant with the
characters of radon production in that environment. Increased
methane concentrations in gas above the fault zone implies a
permeable  zone  for  gas  emanations.  Similarly,  the  negative
anomaly of SP indicates a water drainage process in the fault
zone.  The  curve  of  PEE  shows  a  local  maximum  above  the
fault  zone,  that  indicates  mechanic  stress  in  the  local  part  of
the fault system which is the source of the measured electro-
magnetic field. The resistivity curves measured by VLF (deeper
range)  and  DEMP  (shallower  range)  specify  the  location  of
the  contact  zone  between  the  Tatric  crystalline  rock  of  the
Stražovské  vrchy  Mts  (Fig. 9  –  block  A)  and  the  Cenozoic
deposition of the HND.

Opatovce geophysical profile

The results obtained on this profile demonstrate very similar

geophysical characteristics to the previous profile (Malinová).
The fault zone divides the Pontian/Pliocene Lelovce Forma-
tion from the Upper Pleistocene to Holocene alluvial deposi-
tion. Increased intensity of the PEE fields is found at the foot
of the mountains and also approximately 50 m from Holocene
alluvial plane. The first peak is interpreted as a gravity mass
flow towards the alluvial plane; the second one is a real dis-
crete boundary of the Malá Magura fault. The shape of the
VLF and DEMP curves document the sharp change between
the rock mass of the mountain front and the depression. Radon

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measurement carried out
in this profile shows that
the mountain front has a
lower  radon  content  in
the soil atmosphere than
the  alluvial  plane.  The
maximum  of  the  radon
emanation  is  located
above  the  Malá  Magura
fault  zone,  it  is  consid-
ered to be of tectonic or-
igin.  The  shape  of  the
SP  curve  is  character-
ized  by  lower  values  in
the  mountain  front  and
higher  values  in  the  de-
pression (Fig. 10).

Discussion

Ruptures in the zone

of  an  active  normal
fault  can  be  character-
ized as a series of linear
fault  segments  separat-
ed  by  transfer  zones
with  more  complex  ge-
ometries.  The  linear
trend  results  from  the
fact  that  most  normal
faults  intersect  the  sur-
face  at  high  angles;  the
dip is generally 60° and
more.  It  means  that  the
map trace of the fault is
only  slightly  affected
by  surface  topography.
In  many  cases,  normal
faults also approximate-
ly define a boundary be-
tween

erosional

domain in the uplifted
footwall and a deposi-
tional, nearly horizontal
domain above the down-
thrown

hangingwall.

Fig. 9. The Malinová geophysical profile. Shape of the curves of Rn and CH

concentration in soil air; resis-

tivity (deeper) and phase shift curves from VLF and resistivity (lower) curve from DEMP; SP and PEE
curves and interpreted vertical cross-section along the profile constructed by the VES method. Contact be-
tween crystalline basement of the Strážovské vrchy Mts and the Horná Nitra Depression have the form of a
fault zone with unconsolidated tectonic breccia.

Currently, horizontal movements along dislocation cannot

be excluded, although no reliable data confirming their exist-
ence has been discovered. An indirect argument for the strike-
slip  movement  tendencies  emerges  from  orientation  of  the
fault  within  the  recent  stress  field.  The  movement  along  the
Malá Magura fault can be characterized by oblique slip move-
ment (combination of left-lateral and normal slip components)
which  was  the  result  of  the  ENE—WSW  relative  tension  and
minor  NNW—SSE  relative  subhorizontal  compression.  How-
ever, geophysical characteristics of the fault zone identified at
two transversal profiles indicate a recent extensional regime of
the Malá Magura fault zone (Figs. 9, 10). Taking into account

This is also the case of the Malá Magura fault, which creates a
linear tectonic boundary between two different domains.

Heights and stages of dissection of triangular facets are in-

dicative of relative tectonic activity (Bull & McFadden 1977).
Basal sections of triangular facets may resemble degraded fault
planes (Ellis et al. 1999; dePolo & Anderson 2000; Bull 2008).
Heights  of  basal  triangular  facets  originating  on  the  western
side  along  the  Malá  Magura  Mts  are  between  180—400 m
above the alluvial plain of the HND. Comparison of these data
with  known  normal  fault  slip  rates  (dePolo  &  Anderson
2000), it is possible to set approximately vertical slip rate be-
tween 0.3—1.1 m · kyr

—1

(from the south toward the north).

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Fig. 10. The Opatovce geophysical profile. Shape of the curve of Ra
concentration in soil air; PEE and SP curves; resistivity (deeper)
and phase shift curves from VLF and resistivity (lower) curve from
DEMP and interpreted vertical cross-section along the profile con-
structed by the VES method. The fault zone is also extensional as
on the Fig. 9 and is filled by blocky breccia.

the described changes of the Cenozoic tectonic stress field in
the Horná Nitra area (Hók et al. 1995), as well as in the wider
region  of  the  Western  Carpathians  (e.g.  Marko  et  al.  1995,
2005;  Fodor  et  al.  1999;  Pešková  et  al.  2009;  Vojtko  et  al.
2010)  a  multi-stage  evolution  of  the  Malá  Magura  disloca-
tion is considered. The recent fault is a reactivated Neogene
dislocation, an inherited fault, acting mostly as a basin open-
ing  dislocation,  but  also  as  an  accommodation  structure  of
neotectonic deformations.

Young tectonic movements can be observed from the Pon-

tian to the Late Pleistocene times. The age of the Quaternary
alluvial fan deposits is based upon their superposition, the age

of  travertine  mounds  is  based  upon  biostratigraphical  data
(Kernátsová  in  Gajdoš  et  al.  2005).  However,  more  precise
dating of alluvial fans and the Lelovce Formation for more ex-
act  timing  of  the  HND  neotectonics  is  needed.  For  example,
application  of  cosmogenic  nuclides  to  date  alluvial  fans  is
highly  recommended  for  the  future.  The  Lelovce  Formation
(Pontian—Pliocene?) is the youngest widespread formation in
the  HND  and  was  used  for  neotectonic  studies,  because  the
faults  which  disrupted  this  formation  were  considered  to  be
neotectonic faults.

Conclusions

The morphotectonic, geological, sedimentological, structur-

al,  and  geophysical  pieces  of  evidence  of  the  Malá  Magura
fault  Quaternary  activity  have  been  summarized  herein.  The
fault  is  a  typical  mountain  front  dislocation,  which  separates
the Strážovské vrchy Mts and the HND. This distinct disloca-
tion is attended by contrasting landforms and their parameters.
The  low  S-index  about  1.10  (Fig. 6),  well-preserved,  at  least
two generations of faceted slopes along this fault (Fig. 7), and
convex-linear  longitudinal  river  valley  profiles  (Fig. 8),  the
presence of low-destructed mountain front line are typical fea-
tures for the Quaternary active fault systems.

The results of geophysical methods specified the location of

the  Malá  Magura  fault  and  brought  additional  information
concerning  the  character  of  the  fault  zone.  The  present-day
fault  is  considered  to  be  a  normal  fault,  steeply  dipping  to-
wards the east. The Malá Magura fault is permeable for gases
because the soil atmosphere, above the fault zone, contains in-
creased contents of methane and radon.

The present-day tectonic stress in the Horná Nitra region

was reconstructed by paleostress analysis and determined by
analysis of geomorphological phenomena. The maximum
principal horizontal compressional stress S

was computed to

be in a NNW—SSE direction, the minimum principal horizon-
tal compressional stress S

is perpendicular to this direction.

This stress-field generates predominantly normal, oblique-slip
movement along the Malá Magura fault (Figs. 9, 10) and the
north-west segment of the Pravno fault, respectively.

The Quaternary tectonic activity of the Malá Magura fault is

characterized  by  irregular  movement.  At  least  two  stages  of
important  tectonic  activity  along  the  fault  can  be  distin-
guished.  The  first  stage  was  tentatively  dated  to  the  Early
Pleistocene by alluvial fans distribution, travertine production
(Fig. 2) and morphometric criteria (Figs. 7, 8). The relatively
small  Lower  Pleistocene  alluvial  fans  were  deposited  at  the
foot  of  the  mountain  front  during  increasing  fault  movement
(Burbank  &  Anderson  2001).  However,  the  denudation  of
these alluvial fans is not excluded. The second stage of tecton-
ic activity can by dated to the end of the Würmian and the ear-
liest Holocene, based on the alluvial fans which are arranged
at the foot of the mountain front (Fig. 2).

All the above mentioned attributes of the Malá Magura

fault  and  knowledge  of  the  current  tectonic  regime  play  an
essential role in natural hazard assessment, especially in the
risk  assessment  of  fault  activity.  It  should  be  important  for
local  developments  because  it  was  a  paleoseismologically

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active fault zone which may be active in the present and fu-
ture and generate small to medium-magnitude earthquakes.
Due to detected radon emanations and possible electromag-
netic wave generation by hydrodynamic processes within the
permeable Malá Magura fault zone, the monitoring of the
about 150 m wide zone following the surface fault trace can
be important.

Acknowledgment: This work was supported by the Slovak
Research  and  Development  Agency  under  the  contract
No. APVV-0158—06.  Some  data  reprocessed  in  this  study
have  been  gained  during  the  state  project  solution  Final  re-
port  of  subproject  “Impact  of  building  materials,  construc-
tions  and  geological  factors  on  life  quality”  of  state
programme V and V 2003 SP 28/OSO 0066/000 00 00 “Life
quality – health, food and education”; partial task “Neotec-
tonic  activity”.  We  are  indebted  to  Prof.  W.  Zuchiewicz,
Prof. M. Bielik and Dr. A. Panáček for careful reviewing and
suggestions to improve this article.

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