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Contributions to Geophysics and Geodesy Vol. 48/1, 2018 (1–21)
Applications of shallow seismic refraction
measurements in the Western
Carpathians (Slovakia): case studies
Bibiana BRIXOV´
A, Andrea MOSN´
A, Ren´ePUTI
ˇ
SKA
Comenius University in Bratislava, Faculty of Natural Sciences,
Department of Applied and Environmental Geophysics,
Mlynsk´a dolina, Ilkoviˇcova 6, SK-84215 Bratislava, Slovak Republic;
e-mail: kytkova1@gmail.com
Abstract: Shallow seismic measurement, specifically seismic refraction tomography, is
an effective geophysical method that has applications in various sectors. It enables the
search for and determination of the course of the interfaces, thus helping to resolve geolog-
ical, environmental, hydrogeological, engineering, geotechnical and other problems. The
paper demonstrates the possibilities of using these methods through examples of shallow
seismic measurements that have been performed at various four locations in the Western
Carpathian Mountains. The first case study describes Monastery Pond at Katar´ınka. It
was found that, the basement of the Monastery pond is at a depth of 2–3 m below the
surface and the results were also confirmed by electrical resistivity tomography (ERT).
The next measurement through the thermal power station waste storage showed that
the storage area base runs at a depth of about 20 m under the measured profile. The
third case study addresses the depth of groundwater depth in the area of Borsk´an´ıˇzina.
The measurement confirmed the assumed depth of ground water level at 3.35 m below
the surface. In the last case study, border fault between the Turiec Basin and the Mal´a
Fatra Mts. was mapped by application of shallow refraction methods. The results show
that shallow seismic methods shed light on the problem and in combination with other
geophysical methods are an effective tool with great potential. They provide very useful
data for shallow mapping applications.
Key words: refraction seismics, seismic refraction tomography, shallow seismic measure-
ments, Western Carpathians, case study
1. Introduction
In the past, seismic methods were mainly associated with hydrocarbon ex-
ploration, whose main benefit is their large depth range. On the other hand
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doi: 10.2478/congeo-2018-0001
Brixov´a B. et al.: Applications of shallow seismic refraction . . . (1–21)
the shallow refraction measurements were used to determine the parameters
of the low-velocity layer for the treatment of processing for deep reflection
seismic profiles.
Shallow seismic methods have historical roots dating back to the 1930s,
when limited shallow refraction work was performed using the Intercept-
Time method (Steeples, 2000). The development of technology in both the
acquisition and processing has led to substantial progress in the use of shal-
low seismic measurements since 1980 (Steeples, 2000; Steeples and Miller,
1990).
The use of surface waves has also evolved. These waves which overlap
the useful signal and have to be filtered out in reflection and refraction
processing (especially in the shallow parts of the profiles), have found ap-
plication in shallow research methods such as a SASW (Spectral Analysis
of Surface Waves – Nazarian et al., 1983) and MASW (Multichannel Anal-
ysis of Surface Waves – Park et al., 1998, 1999; Xia et al., 1999, 2000).
The use of shallow seismic measurements is excellent, particularly for de-
termining the depth or course of geological interfaces for different purposes:
(a) for geo-engineering, geotechnical investigation and the assessment of
landslide areas (e.g., Beng et al., 1982; Shtivelman, V., 2003; Cardarelli
et al., 2014; Coulouma et al., 2012; Hack, 2000; McClymont et al., 2016);
(b) for hydrogeological purposes (e.g., Haeni, 1986; Gordon, 1997; Gabr et
al., 2012; Osumeje and Kudamnya, 2014; Pandula, 2000; Shtivelman, 2003;
Prekopov´a et al., 2016); and (c) for archaeological exploration (e.g., Tsokas
et al., 1995; Shtivelman, 2003; Henley, 2003; Shahrukh et al., 2012).
The basic parameter for the successful use of seismic methods for any
purpose is to achieve the possibilities and limitations of these methods.
In some cases, the geological layers cannot be detected (Soske, 1954 and
Sander, 1978 in Haeni, 1986). One of the criteria is an insufficient velocity
contrast of layer or thickness in order to return first arrival energy (Haeni,
1986). This is related to the vertical resolution of the method. Seismic
method vertical resolution depends on the generally accepted one-quarter
wavelength axiom (after Widess, 1973 in Nanda, 2016). If the thickness of
a layer is less than one-quarter of a wavelength of the incidence wave, the
thin bed will not be visible on the time–distance graph (Reynolds, 1997).
Because the wavelength is a ratio of wave velocity and frequency, in a rock
environment with a wave velocity of 2000 m/s and a frequency of 50 Hz, the
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vertical resolution will be approximately 10 m. Layers thinner than 10 m
will not be detected. The vertical resolution decreases with depth because
of the attenuation signal of the higher frequency component and higher ve-
locities (Nanda, 2016). Better resolution can be expected in shallow parts of
the environment. Vertical resolution is attainable with a reflection of about
10 cm as described in Steeples (1998). The vertical resolution is sometimes
referred to as a percentage of the practical survey depth. For refraction
measurement it is presented as 10–20% of depth (Enviroscan, 2018). Survey
depth for refraction seismic is deposed as 1/5 to 1/4 of the maximum offset
(shot-geophone separation) (Enviroscan, 2018). The appropriate spacing of
geophones is an important parameter for layer detection by seismic refrac-
tion (Reynolds, 1997). If the distance between geophones is too large, there
is not enough sampling for an identification of the layer on time-distance
graphs. This is another layer problem. In planning for the use of seismic
refraction measurement, one must be aware of another limitation of this
method. Based on the principles of the propagation of seismic waves and
the conditions for critically refracted wave occurrence, refraction seismic
measurements are only able to detect layers when velocity increases with
depth (Reynolds, 1997).
The most commonly used shallow geophysical methods, especially for
non-demanding terrain measurement, are electrical resistivity tomography
(ERT) and georadar. However, as one of the selected case studies has shown,
these methods are not always successful. Therefore, the aim of this article
is to demonstrate that shallow seismic methods have a wide range of appli-
cations and are equivalent methods for various shallow survey application.
This paper provides case studies from four different locations in the West-
ern Carpathians (Fig. 1). The first case study relates to an archaeological
research on the marginal part of the Mal´e Karpaty Mts. The goal is to
map the basment of Monastery Pond. The next case study deals with an
environmental issue, namely, waste storage at a thermal power station. The
third case study maps the tectonic contact of the Turiec Basin with the
Mal´a Fatra Mts. The last case study features an example of using the shal-
low seismic methods for hydrogeological purposes. It is aimed at searching
for the surface of underground water levels.
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Fig. 1: Geological scheme of the Western Carpathians (after Bielik, 1998 and Geological
map of Slovakia, 2013) with marked case studies localities. MK – Mal´e Karpaty Mts.,
BN – Borsk´an´ıˇzina, TB – Turiec Basin, MF – Mal´a Fatra Mts.
2. Methodology
Refraction seismic methods use controlled source seismic waves, specifically
refraction waves, to determine depths to the interface within the subsurface
and the velocities of the layer between the interfaces (Lillie, 1999). In seis-
mic refraction surveys on land, a number of geophones are laid out along
a cable in a straight line. In the simplest case, the seismic source (shot) is
located at the beginning and end of a geophone line. The source can also be
positioned at a location along the geophone spread, or at a discrete distance
from the end of the spread. The positioning of shots provides adequate lat-
eral resolution (Reylnolds, 1997).
The seismic refraction tomography profile (SRT) requires a higher den-
sity of sources and receivers than in conventional surveys to obtain high
resolution profile.
The seismic waves spread from the source and the arrival of each wave is
detected along the set of geophones. Direct waves and waves critically re-
fracted from interfaces are useful for refraction seismic interpretation. The
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direct wave comes to geophones as the first to the offset known as the
crossover distance. After this offset, critically refracted waves precede the
direct wave. During processing, these first arrivals are marked for each
geophone on a seismograph. They are associated with travel times and
plotted on a time-distance graph. The gradient of this graph changes at
the crossover distance from the slope of direct wave arrivals (characterized
by the velocity of direct wave) to the slope for refracted signals. The time–
distance graphs are then used to calculate the velocity of the interpreted
layers and the depth of the interfaces. Several different interpretational
methods for seismic refraction have been published. In Reynolds (1997),two
methods emerge as the most commonly used are the ‘plus-minus’ method
(Hagedoorn, 1959) and the generalized reciprocal method (Palmer, 1980).
Seismic refraction tomography is an alternative to conventional seismic
refraction analysis methods (Sheehan et al., 2005). Conventional refraction
methods assume that seismic velocity structures are simple and primarily
attempt to map a refractor. Tomography methods calculate travel times
and raypaths in a regular grid model and use an inversion technique to re-
construct seismic velocities (Zhang and Toks¨oz, 1998). In the case of 2D
refraction vertical tomography, the starting model must first be generated.
Ray tracing is used for the calculation of travel times for this model. The
synthetic data obtained by ray tracing are compared with the field data and
the initial model is modified until the best fit between the model and field
data is achieved.
Acquisition and processing
The data for seismic refraction tomography at the Katar´ınka archaeological
site was obtained by a 24-channel DMT equipment with 10 Hz geophones
and a hammer with 5 stacks as the source served for better resolution. In
the other cases, a 36-channel M.A.E. A6000-S equipment with 4.5 Hz geo-
phones and a hammer as a source was used.
The measured data were processed in Reflexw Version 8.0 software (de-
veloped by Sandmeier, 2016) for the processing of seismic, acoustic or elec-
tromagnetic reflection, refraction and transmission data. At first, the SEG-2
data were imported to the software background for refraction processing and
the first arrivals were picked (see Fig. 6b). Then the time-distance curves
were created from the picked travel times, and the slopes of primary wave
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curves and refracted curves from various interfaces were marked for each
shot (see Fig. 5a and Fig. 6c). After this analysis and interpretation of first
arrivals, the velocity model of the subsurface environment was created. This
served as the initial model for seismic refraction tomography. The result of
tomography is a velocity model with a continuous velocity gradient across
a subsurface which is interpreted depending on the specific case study.
Some examples also show the influence of various factors, such as the
changing humidity of the rock environment or its consolidation, to ob-
tained velocity values in the shallow survey. Interpreted velocity interfaces
have been verified by other geophysical measurements (mainly ERT) in the
Katar´ınka and Bystriˇcka areas.
3. Case studies
3.1. Mapping the bottom of Monastery Pond at the Katar´ınka
site
Katar´ınka is a famous archaeological site around the ruins of Saint Cather-
ine’s Abbey (founded in 1618) on the hills of the Mal´e Karpaty Mts. near
the village of Dechtice (Figs. 1 and 2). Intensive geophysical research was
conducted in this area in 2009 (INCA, 2009 – International Course on Ar-
chaeoGeophysics) to help find buried ruins of buildings near the monastery,
surrounding chapels, a cavern under the presbytery and others. As a con-
tinuation of this research, seismic refraction measurements and ERT were
applied to identify the bottom of Monastery Pond.
From a geological point of view, the entire archaeological site is located
in the territory of the Brezovsk´e Karpaty Mts., which belong to the Mal´e
Karpaty Mts. The Brezovsk´e Karpaty Mts. are mostly comprised of Meso-
zoic rocks. Triassic sediments are dominant, while Jurassic and Cretaceous
sediments are less preserved. The Triassic sediments belong to the Ned-
zov Nappe Jablonica Group (Salaj et al., 1987). In area of abbey ruins
bloom out light-grey bedded Wetterstein Dolomite (Ladinian-Kordevolian)
(Geological map of Slovakia, 2013). Neogene and Quaternary deposits ex-
tend to the edge of the mountain range. Quartery deposits are represented
by fluvial sediments of alluvial flats (deluvial and eolic sediments, loesses).
Neogene sediments, in the prospecting area are represented by Lakˇs´arska
Nov´a Ves Formation – Jablonica Conglomerates (polymict conglomerates,
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Karpatian) (Salaj et al., 1987; Geological map of Slovakia, 2013).
The seismic profile is situated southwest of the Abbey ruins, in the area
where the pond was assumed on the basis of historical documents. Ac-
cording to documents in the State Archives in Bratislava, Matulov´a (2003)
states that the pond dimensions are about 49 ×31.36 m. Remnants of the
pond barrier are still visible in the terrain. Two 46 m long profiles in the
SW–NE direction with 12 overlapping geophones for seismic refraction data
acquisition were used for this survey (Fig. 3a). Geophone spacing at both
profiles was 2 m. Shot points were placed along each profile at a distance
of 2 m, with a beginning of excitation −2 m from the first geophone and
the final shot being 2m beyond the last geophone. The ERT was measured
at a 94 m long profile with 1-m electrode spacing. The Schlumberger and
dipole-dipole resistance methods were used. The Seismic and ERT profile
began at the same point and had the same course. Measurements were made
Fig. 2: Location of the Katarinka monastery area on a detailed geological map (after Salaj
et al., 1987 and Geological map of Slovakia, 2013).
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on different days. If both methods can be measured together, the parallel
profiles sufficiently distanced from each other should be used because of the
degradation of the signal-to-noise ratio at geophones due to ERT measure-
ment.
The sought after pond floor was interpreted by the velocity refraction
profile, ERT profile, and seismic reflection profile (Fig. 3). Based on the
Fig. 3: Results along the seismic and ERT profile at the Katarinka case study locality.
a) velocity model, b) SRT and c) ERT.
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measured P-wave velocity (Vp<700 m/s) and the resistance (<100 Ω.m),
the thickness of the surface sediments (scree, vegetal soil), that probably
filled the pond space after the collapse of the monastery was determined.
The bottom of the pond is anticipated to be at a depth of 2–3 m below
the surface. At the bottom of the low velocity layer the conglomerate or
dolomite rock bottom should be interpreted. In the upper part next to the
surface sediment layer, the disturbed and wetted rocks are assumed due
to a relatively low Vpand resistance values. The velocities m/s measured
mainly in the NW section of the profile at a depth of 7–8 m correspond with
standard Vp values for dolomites or conglomerates (dolomites and conglom-
erates have mostly the same standard velocity and resistivity range). In the
case of dolomites, this can be a continuation of the occurrence of a Wet-
terstein dolomite rising to the surface at the church ruins. The same result
can be interpreted on the ERT profile.
3.2. Estimation of the thickness of coal ash and the run of the
bottom at the thermal power station ash storage area
This seismic profile passes through the thermal power station waste storage
area. The area of interest consists of a hill of coal ash stored on loam cover
on a surface of approx. 0.67 km2. The area surrounding the dump is mostly
formed by Quarternary fluvial sediments (Fig. 4), mainly fluvial plain fine-
sandy loam to fine-grained sands or lithofacially undivided loam (Geological
map of Slovakia, 2013).
The acquisition for seismic refraction tomography was performed on nine
overlapping lines each of 175 m in length. The geophones were distributed
at 5 m intervals, the acquisition lines lap was comprised of 12 geophones.
The source position moved at 20 m intervals. The first shot was acquired at
a distance of 20m in front of the first geophone on the first seismic line. The
entire length of the geophone line was 1135 m across the waste storage area
(Fig. 4, Fig. 1). There was no ERT measurement because of unsatisfactory
findings from the past.
The velocity model of the seismic refraction tomography section clearly
shows the thickness and geometry of the ash storage area (Figs. 5b,c).
A pronounced change in lithology is indicated by an increase in Vpfrom
∼500 m/s to about 1600 m/s. P-wave velocities in several parts of the ash
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Fig. 4: Location of the thermal power ash storage area and investigated profile on a
detailed geological map (after Geological map of Slovakia, 2013).
storage area vary from 200 m/s to 560 m/s depending on the consolidation
of material, and ultimately to a variation of material moisture (as seen in
Figs. 5b,c). At a length of 520–560 m the storage area is divided into two
parts. The partition is shown on the velocity model as a zone of higher
velocities (450–500 m/s). In the left part of the storage area the velocities
are approx. 350 m/s. The velocities in the right part are very similar, but
there is a depression on the surface and in area of depression slopes the ve-
locities are lower (≤300 m/s, 200–300 m/s). The surface water drains from
the slopes and remains at the depression bottom. The velocities are then
slightly higher at the bottom of the depression (∼380 m/s) than in other
flat parts. There is also an increase in Vpto values of about 380–400 m/s at
the edges of ash storage area. This should also indicate high ash humidity,
but it is likely caused by a consolidation of storage slopes. The storage area
base runs at a depth of about 20m under the measured profile. The velocity
on the ground is about 1600 m/s. Higher values are recorded in the right
part of the section. These values correspond to ambient Quarternary fluvial
sediments.
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Fig. 5: Results along the seismic profile through the ash storage area. a) selection of time-
distance graphs of some shots along the profile and pointing of some account apparent
velocities, b) velocity model with velocity interface interpreted as a storage basement and
c) SRT.
3.3. Determination of groundwater level
The survey was located in the western part of Slovakia near a village in
the area of Borsk´an´ıˇzina (Fig. 1). Since there was a shallow borehole with
available data close to the measured profile, the velocity output could be
directly correlated with geological information (Fig. 6a).
The thirty-six geophones were spaced at 3 m intervals along a straight
profile with a length of 105 m, and 12 shots were measured 12 m from each
other. The first shot point was at 24 m in front of the geophone line,
while the shallow borehole was in the middle of the geophone line length
(Fig. 6d,e). According to the borehole data, the groundwater level was ex-
pected at a depth of 3.35 m below the surface, while an interface of wet sand
and Neogene clay was anticipated at a depth of 8 m.
Results and some examples of processing steps are shown in Fig. 6. The
distribution of velocity values in the seismic section correlates with borehole
data. Both records, the standard refraction model (Fig. 6d) and the tomog-
raphy model (Fig. 6e), clearly reveal the level of groundwater. The low
velocity layer (<1000 m/s) is interpreted as dry sand. There is an increase
in speed at a depth of 3 m (>1500 m/s). This indicates the onset of wet
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Fig. 6: Results and data along the seismic profile to determine ground water level. a) Well
situation, b) example of seismogram with picked first arrivals, c) time-distance graphs of
some shots along the profile, d) velocity model and e) SRT.
sand. The next interface – wet sand/Neogene clay, is not recorded at the
velocity sections. We expected such result given the assumed low velocity
contrast between these two layers.
3.4. Mapping of border fault between the Turiec Basin and the
Mal´a Fatra Mts.
This case study is focused on the development of the tectonic contact of the
Turiec Basin with the Mal´a Fatra Mts. specifically, the determination of the
position of the Hradiˇste fault zone.
The Mal´a Fatra Mts. is part of the Western Carpathians situated in the
westernmost part of Slovakia. It is a typical core mountain range with a
crystalline core, while its northern side and slopes are overlaid by a Meso-
zoic cover (F¨oldvary, 1988). The Mal´a Fatra Mts. is divided into two parts
–L´uˇcansk´aMal´a Fatra Mts. (the southern part) and Kriv´anska Mal´aFatra
Mts. (the northern part). The crystalline core in the L´uˇcansk´aMal´aFatra
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Mts. part (F¨oldvary, 1988) consists of granitoids (granite-gneiss, biotite-
oligoclase granite, granodiorite, quartz-diorite, Magura type granite) and
metamorphics (mica schists of Jaraba Group and migmatites).
The south-east L´uˇcansk´aMal´a Fatra Mts. region is adjacent to the Turiec
basin. The Turiec basin is an approximately 40 km long and 10 km wide lo-
cated between the Mal´a Fatra Mts. and Vel’k´a Fatra Mts. (F¨oldvary, 1988).
The pre-Neogene basement consists of the paleo-Alpine alochthonous Meso-
zoic complexes, and Paleogene post-nappe sedimentary cover in its northern
part (Fus ´an et al., 1987; Kov´aˇc et al., 2011; Bielik et al., 2013). The re-
maining part of the basin (F¨oldvary, 1988) is filled by Neogene (Pliocene
lacustrine and fluviatile deposits, Miocene sandstone and grit) and Quater-
nary sediments (Holocene alluvium, Pleistocene loess and fluvial gravel).
The eastern and western edges of the Turiec Basin are sharply delimited
by fault planes (F¨oldvary, 1988). The north-eastern corner is fragmented by
SW–NE oriented faults considered to be pre-Quaternary in origin (F¨oldvary,
1988). The Hradiˇste fault zone is one of the basinal faults. Its course is
not striking on the surface. We attempted to determine its location on a
measured shallow seismic profile.
The NW–SE seismic profile of a total length of 440 meters was located
SW of the city of Martin above the village of Bystriˇcka (Fig. 7, Fig. 1).
Data were measured by three overlapping lines, each 175 meters long with
12 geophones at the cover. The geophone interval for each line was 5 m
and the source points were spaced 10 m along the geophone line starting at
2.5 m in front of the first geophone. For better resolution, 7 to 12 stacks
were used for each shot.
At first, the typical signatures that the fault impacts on first arrivals as
described by Yan et al. (2005) were observed on the time–distance graph.
The reverse branch which exists far from the fault on the footwall on all
shots and an unusual velocity variation pattern for the shot on the hanging
wall can be seen (Fig. 8a).
The lateral change in velocities in the refraction velocity profile indicates
significantly the Hradiˇste fault (Fig. 8b and also Fig. 8c). A layer with low
velocities is found at the top along the entire profile. It can be interpreted
as soil and unconsolidated sediments. However, we are interested in the ver-
tical contact of two velocity zones at a depth of approximately 10 m below
the surface. A zone with velocities up to 3000m/s appears on the left part of
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Fig. 7: Location of seismic profile up to the mapped Hradiˇste fault on a detailed geological
map (after Geological map of Slovakia, 2013).
the profile and can be interpreted as the granitoid rocks which are common
in this area. The lateral change in velocity of about 160m to the right along
the measured profile and the zone of lower velocities (2000–2500 m/s) are
interpreted as Neogene sediments.
4. Discussion
It is well known that the geophysical results, if possible, would be verified by
complex different geophysical methods. Because of the high sensitivity of
geophones to any noise, doing seismic measurements with other geophysical
measurements on the same profile at the same time can be problematic.
ERT is a frequently used method in combination with seismic measure-
ments in shallow geophysical research (Riddle et al., 2010; Leucci et al.,
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Fig. 8: Results along the seismic profile through the Hradiˇste fault. a) selection of time-
distance graphs of some shots along the profile (the dashed line and framed zone highlights
fault impact on first arrivals), b) velocity model and c) SRT profile.
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Brixov´a B. et al.: Applications of shallow seismic refraction . . . (1–21)
2007; Gabr et al., 2012; Shahrukh et al., 2012; Basheer et al., 2012; Hell-
man et al., 2017). These two methods can be measured together at the same
time, but parallel profiles at a sufficient distance from each other should be
used to avoid the degradation of signal-to-noise ratio at the geophones due
to ERT measurement.
In the case of mapping the Hradiˇste fault, well preserved outcrops, bore-
holes and geophysical data were available (Kov´aˇc et al., 2011; Kuˇsnir´ak
et al., 2018). The course of this fault was mapped by several geophysical
methods. The data and results presented in this article were re-measured as
another device with different equipment and acquisition geometry. It fea-
tured the use of 4.5Hz vertical geophones which are often used for MASW.
Geophones of 10–12 Hz are generally used for such a survey. However,
the use of low frequency geophones and the larger step of geophones and
shots (compared to older measurements during the multimethod geophys-
ical study), did not have a major effect on the results of measurements in
this case. Seismic refraction tomography and the effects on time-distance
graphs map the fault successfully.
There is not always complete agreement between results obtained by dif-
ferent geophysical methods. In shallow measurements, interpretation may
be influenced by various surface factors such as elevated humidity in the
surface areas in a rainy season or by the disturbance and weathering of the
rock bottom. The shallow zones are also often influenced by human activity.
All of these affect the detected velocity values. In the case of the Katar´ınka
measurements, there is no complete match over the interpreted pond bot-
tom in the ERT profile and the seismic profile along the area which is about
50–70 meters of measured profile. The low resistance values recorded in this
area in the surface layer on the ERT profile are apparently associated with
increased humidity. The measurement was made after the rainy season, and
water appears to flow in these places. It also influenced the detected Vp.
There are higher values in this zone, which influences the continuance of
the interpreted interface (it is interpreted at a slightly smaller depth than
ERT).
In the case of the thermal power station, the ERT measurements were
made first for the detection of the bottom of the ash storage area in the
past, but it did not yield the desired results. The entire environment was
too conductive and no interface was recorded. As shown by the results of
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seismic measurements in this paper, seismic refraction tomography was an
excellent alternative to achieving the desired findings.
5. Conclusion
These case studies demonstrate clearly that even shallow seismic refraction
methods are valuable tools for research in several areas. Shallow seismic
refraction tomography is an ideal method for areas characterized by strong
lateral velocity gradients, and thus an effective tool for vertical fault explo-
ration and mapping. It also can play an important role in ground water
level estimation, environmental studies of waste storage and archaeological
studies. By performing shallow refraction methods (especially SRT), a de-
tailed view of velocity distribution and thus the geological structure of a
subsurface can be obtained. It is a cost effective, non-destructive method
which also reduces the cost of surveys that use it. However, as in the case
of other geophysical methods, it requires input geological and geomorpho-
logical information. It is also suitable to verify the seismic interpretation
by other geophysical methods. The SRT and ERT represent an appropriate
combination which brings satisfactory results and can be measured together
by a parallel profile sufficiently distant from each other.
Acknowledgements. This work was supported by the Slovak Grant Agency
VEGA, grants No. 1/0559/17, 1/0462/16 and 2/0098/18, and by the Slovak Research and
Development Agency under grants No. APVV-0129-12 and APVV-16-0146. We thank the
Comenius University Science Park for providing the equipment.
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