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Examples of the application of microgravity mehtod for the detection of potentially hazardous (empty) underground cavities caused by the collapse of coal mines are presented. Within these areas some alteration by previous remediation activity had occurred. This was not documented earlier and, therefore, such alteration was often unknown prior to the current investigations. We show a successful application of microgravity, leading to the detection of an empty cavity, in close proximity to where concrete injection was earlier performed. This was subsequently verified thorugh measurements in a borehole. In contrast, two other examples delivered results where the microgravity data, along with signals from other geophysical methods, led to the interpretation that subsidence resulting in the formation of sinkholes had been in‐filled, and in these situations the detection of more recent cavities was considered to be unreliable. These results point to the conclusion that microgravity interpretation of cavities is an effective approach, but the success of this approach may be compromised at sites where remediation activity has already occurred; in such situations the approach should be supplemented by other geophysical methods.

ZusammenfassungDie Vorauserkundung der geologischen Bedingungen vor der Ortsbrust stellt noch immer eine Herausforderung im Tunnelbau dar und bedarf zusätzlicher Forschung, um die derzeit existierenden Methoden zu erweitern und verbessern. Allerdings gestaltet sich diese Weiterentwicklung auf aktiven Tunnelbaustellen oft schwierig, da sie mit einer Behinderung der Vortriebsarbeiten verbunden ist. Das neu errichtete Zentrum am Berg bietet eine Möglichkeit, diesem Problem zu begegnen. Die maßstäbliche Großforschungsanlage in Eisenerz bietet Raum, um solche Experimente in einer realen Umgebung durchzuführen. Die ersten Daten (Refraktionstomographie, passives seismisches Monitoring, Bohrlochradar) wurden bereits vortriebsbegleitend erhoben. Um die Mächtigkeit der plastischen Zone festzustellen, wurden Bohrlochradarmessungen an zwei radialen Messquerschnitten sowie Refraktionstomographien an zwei Abschnitten entlang der Tunnelwand aufgenommen. Für die Korrelation petrophysikalischer und geotechnischer Parameter wurden darüber hinaus Laborversuche durchgeführt. Das passive seismische Monitoring wurde während des konventionellen Vortriebs eingesetzt, um die Signale der einzelnen Arbeitsschritte zu analysieren und die Eignung des Bohrsignals als seismische Quelle näher zu beleuchten.

We employed integrated methods to assess the landslide movement in Sv. Anton town in the Western Carpathians Neogene Volcanic Field (Central Slovakia). The integrated diagnostics required s...

Umbrisols generally develop in a cool and humid climate. Therefore, occurrence of these soils in the Borská lowland of southwestern Slovakia is very uncommon, and this inspired the aim of this paper: Analysis of the natural conditions suitable for Umbrisol development. Umbrisols in the Borská lowland developed from aeolian quartz sands accumulated on Neogenne marine clay sediments. Their occurrence is connected with the groundwater table relatively close to the ground surface and this particularly determines Umbrisol genesis in this area. Sufficient input via organic matter is an important factor for formation of the umbric horizon, and only the rich herbaceous undergrowth of the prevailing planted pine and mixed pine-oak forests is capable of providing it. A growth of diep-rooted grass is closely connected with higher soil moisture content, and quite moist areas occur in the deeper inter-dunes depressions. Constant soil moisture in these sites is facilitated by water capillary elevation. While Umbrisols are transformed to Arenosols at increased altitude, they can be transformed to Gleysols in deep depressions. Herein, induced polarization provided suitable geophysical method for detection of arenic Umbrisol inclusions. Sharp transformation of the humus layer to dry non-polarized aeolian quartz sands enabled the surface horizon to be distinguished by induced polarization

The Tatricum crystalline basement in the northern PovažskýInovec Mts.contains several narrow tectonic slices with different rock composition. Some of themcomposed of the Upper Cretaceous mass flow deposits (the Horné Belice Group) are considered unique within the framework of the Internal Western Carpathians and particularlywithin the Tatricum. Tectonic interpretation of their structural position is longer a matter of debate. Contrasting resistivity properties of the Hercynian mica schists and theUpper Cretaceous sandstones and shales were confirmed by the parametric geophysicalmeasurements. The Hranty section, the structurally highest and most internal UpperCretaceous tectonic slice was investigated by the electric resistivity tomography. Two longitudinal and two transverse resistivity profiles were measured and combined into a3D image which suggests that the low resistivity Upper Cretaceous rocks form relatively shallow and flat lying structures folded and deformed between the crystalline basementslices. &nbsp

International audience; The Hradište border fault zone has played an important role in the development of the tectonic contact of the Cenozoic sediments of the Turiec Basin with the Malá Fatra Mountains crystalline basement. Seismic, geoelectric, radiometric, gravimetric, magnetometric and ground penetrating radar measurements were used to study the physical properties and determine the exact position and inclination of this fault zone down to a depth of up to 40 m. The Hradište border fault zone represents an almost vertical physical boundary characterized by decreasing seismic velocity (from 3.0 km.s−1 to 2.2 km.s−1) and decreasing electrical resistivity (500 to 150 Ω.m) when passing from the basement west of the fault to sediments to its east. It corresponds also to a compact segment of the lowest volume activity of radon 222Rn values in soil air (8 kBq.m−3 on average) and maximum horizontal gravity gradient (−0.0076 mGal.m−1). The discovery of this anomalous zone also helps us to distinguish two different anomalous blocks. The block west of the fault represents the orthogneisses of the Tatric crystalline complex belonging to the Malá Fatra Mountains. The eastern block is built-up by the Bystrička Member Pliocene sediments of the Turiec Basin. Our study serves as a case study for geophysical research on faults in different tectonic units of the Western Carpathians and other similar orogens.

The sedimentary filling of two Slovak Neanderthal sites – the Prepostska Cave near Prievidza (Micoquian) and the Certova Pec Cave near Radosina (Szeletian, Mousterian) was investigated, while archaeological and palaeontological studies have shown these caves are very important sites from the viewpoint of the ancient man settlements. No geophysical research had previously been conducted here, therefore ground penetrating radar (GPR) and electrical resistivity tomography (ERT) geophysical methods were applied in order to expose its depths for future archaeological and palaeontological field campaigns. The GPR survey at the Prepostska Cave revealed a disrupted zone in the southwest (SW) corner of the investigate area, encapsulated in travertine surrounding the bedrock layer identified at a depth between 0.4 to 2.4 m. This discovered zone is assumed to be an undocumented recent excavation zone. The combined ERT and GPR survey also identified at the Certova Pec Cave, aside from some main structures (large limestone blocks, loamy-clayey sediment in the central part and debris), intact cave sediments, deposited under the debris filling and large limestone block, located at approximately 2 m depth in the back part of the cave, close to its northeast (NE) entrance. These unconsolidated intact deposits represent the lower part of the Mousterian horizon. Thus, the geophysical survey supported previous hypotheses on the assumed existence of deeper layers with potential archaeological and/or palaeontological content, which have since been spatially defined. Copyright © 2016 John Wiley & Sons, Ltd.

Katarinka (St. Catherine) is the ruin of an abandoned Franciscan monastery from the early 17th century located in the western Small Carpathians in Slovakia. Historical sources and paintings suggest that, beside the remains of the monastery that are still visible, a circle of eight chapels, a pilgrim’s hospice, a cemetery, and garden terraces originally surrounded the main building of the monastery. From 2009 to 2012, geophysical campaigns were performed to find evidences and positions of remains of these buildings of the monastery campus. An initial magnetic overview survey revealed multiple local accumulations of disordered dipole anomalies. Since these accumulations did not allow a structural interpretation, ground penetrating radar measurements were conducted. The ground penetrating radar results clearly showed wall structures beneath almost all magnetic anomaly accumulations. In between the remains of the monastery main building, ground penetrating radar and electrical resistivity tomography were performed at different areas that were difficult to access because of a strong cover of vegetation and steep topography.

Summary Geophysical detection and monitoring of subsurface cavities and subsidence effects over sites with mining activities is an very important task of near surface geophysics. Microgravity method can play an important role in the frame of such kind of research and monitoring. In our contribution we bring several examples (residual Bouguer anomalies interpretation) from the application of microgravity method together with other geophysical methods in sites with abandoned mining activities (brown coal mines in southern Austria and central Slovakia). Microgravity research was able to detect important negative anomalies in both cases – the first one was connected with a real migrating mining cavity, the second was probably an old surface collapse filled by debris and mining waste (both objects have been verified by in-situ drilling). Application of other shallow geophysical methods (electro-magnetic induction, electrical resistivity tomography and shallow refraction seismic survey) in the second case helped us to interpret the received microgravity anomaly in a more correct way.

A complex of geophysical methods were used to investigate a small karst area aimed at the production of detailed geological mapping, to confirm geological localization of known sinkholes, and to find possible continuations of caves and voids below the surface. The dipole electromagnetic profiling and radiometric mapping (the gamma-ray spectrometry method) were applied to determine the spatial distribution of hard carbonate rocks and weathered valley-fill sediments. Detailed high-definition magnetometry was carried out at selected sites in the studied region with the aim of distinguishing between sinkholes and man-made lime-kilns, pits where limestone was heated and transformed into lime. The microgravity and the electrical-resistivity tomography (ERT) methods were used to create high-resolution images of the underground cave. The results of ERT and the geological survey were used as an initial model for gravity modeling. Subsurface cavities of various sizes are contrasting geophysical objects, and the electrical resistivity can range from very conductive to relatively resistive depending on the composition of the filling materials. The interpretation of resistivity properties is not always straightforward. We must distinguish air-filled (high-resistivity) and loamy water-filled (low-resistivity) cavities and fractures. The combined geophysical methodology permits us to determine a more accurate near-surface geological model, in our case the parallel interpretation of a strong conductive anomaly in the ERT inversion and a predominant density decrease in the gravity modelling yield the presence of cavities at depths approximately of 50 to 60 m below the surface.

Geophysical methods offer a broad spectrum of information by dealing with slope deformations. The electrical resistivity tomography (ERT) method is mainly applied for spatial localization of the landslide body and depicting the shear zone position. This article presents the application of the ERT method for the landslide hazardous areas by means of numerical modelling. Four different synthetic models with very small resistivity contrast (30 Ohm.m/50 Ohm.m), where each model represents a different type of slope deformation, were tested by several factors affecting the final inverse model: measurement point density, L1 and L2 norm and L-norm roughness filter components. The higher measurement points density helps mainly to detect the boundaries at greater depths. Inverse models computed using the L1 norm bring satisfactory results for compact anomalous bodies, i.e. water saturated landslide body. In the case of subtle conductive zones, i.e. shear planes, the L2 norm based inversion is recommended. For enhanced reconstruction of skewed anomalous objects, roughness filter including a diagonal component produces more accurate inverse image. The article also demonstrates the ability of the ERT method to detect and describe the shape of the slope deformation even by a relative subtle resistivity contrast

The ruins of the St Catherine's monastery complex, the largest sacral ruins in Slovakia, are an important example of Slovak cultural heritage. The Franciscan monastery was a famous site of religious significance due to the legends describing the apparitions of St Catherine. The preservation project of the monastery remains started in 1994. As a part of this project, complex historical, archaeological, anthropological and geophysical research has been conducted at the site since 1997. Microgravity and ground-penetrating radar (GPR) surveys were carried out in the nave of the former church in order to reveal the position of three aristocratic crypts that served as burial places for the members or higher society in the seventeenth and eighteenth centuries. In the microgravity data processing, a novel method for the calculation of the building correction was employed, where the gravitational effect of the church is calculated using a polyhedral model of the building created from photographs with a special photogrammetric software. Several gravity anomalies were found in the residual Bouguer anomaly map. Semi-automated interpretation techniques including the Euler deconvolution and harmonic inversion have been used to investigate the depth and size of anomalous sources. Results from 36 GPR profiles obtained by a 400 MHz antenna were visualized in the form of horizontal time-slices and vertical time-sections. These images indicate anomalous reflections suggesting potential archaeological targets. Integrated interpretation of results from both geophysical methods has confirmed the presence of a known aristocratic crypt excavated in 2001, as well as two other crypts predicted from historical archives. The combination of microgravity and GPR surveys has proved to be a very effective and non-destructive tool for archaeological research. Copyright © 2013 John Wiley & Sons, Ltd.

Compilation of the Slovak gravimetric database with the actual amount of about 320,000 observation points is presented. Gravity data were collected during more than 50 years, which yields a very heterogeneous dataset, with large variations in the station coverage and processing methods. The regional gravimetric database (more than 212,000 points) was resumed in 2001. The compilation discussed herein (with more than 107,000 detailed gravity measurements) was made during 2011–14. Quality-control process and complete recalculation of the Bouguer anomalies is presented. Primary focus of this project was on a proper recalculation of the terrain corrections. New detected linear features in the Bouguer anomaly map were verified by the field measurements. A new software solution for reconstruction of the gravity acceleration values from the Bouguer anomaly map was developed for geodetic applications.

Downward continuation of potential fields is a powerful, but very unstable tool used in the processing and interpretation of geophysical data sets. Treatment of the instability problem has been realized by various authors in different ways. The Tikhonov regularization approach is one of the most robust. It is based on a low-pass filter derivation in the Fourier spectral domain, by means of a minimization problem solution. We highlight the most important characteristics from its theoretical background and present its realization in the form of a Matlab-based program. The optimum regularization parameter value is selected as a local minimum of constructed L"p-norms functions-in the majority of cases, the C-norms give the best results. We demonstrate very good stabilizing properties of this method on several synthetic models and one real-world example from high-definition magnetometry. The main output of the proposed software solution is the estimation of the depth to source below the potential field measurement level.

Geophysical survey is very useful and popular tool used by engineering geologists to examine landslides. We present a case study from the Kapusany landslide, eastern Slovakia, where a broad spectrum of geophysical methods were applied on several profiles in order to compare the ability of the methods to detect as many landslide’s structural features as possible. The 2D Electrical Resistivity Tomography inverse model was capable to define the geological structure of the landslide and to define the shear zone, however the resolution of the inverse model does not allows us to identify cracks or other minor landslide’s features. These, however, were nicely recorded in the results of Dipole Electromagnetic Profiling and Self Potential method. In addition microgravity was employed to validate the results obtained from electrical methods and afterwards a final geological model, based on the integrated interpretation of all involved methods was constructed. This model will serve as a reference model for long term landslide monitoring using modern geophysical and engineering geological approaches.

Complex of geophysical methods was used to investigate small karst area for purposes to make of detailed geological mapping survey, to confirm geological localization of known sinkholes and pits and find possible continuation of caves and voids below the surface. The electromagnetic (the Electromagnetic Conductivity method – CMD) and radiometric (the Gamma-Ray Spectrometry method) mapping was applied to determine the spatial distribution of hard carbonate rocks and weathered valley-filled sediments. Detailed high-definition magnetometry was realized on selected sites of the studied region with the aim to distinguish between real sinkholes and man-made lime-kilns (unearthed pits, where limestone was heated and transformed into lime), which have been built at the site during the history. The microgravity and the electrical resistivity tomography (ERT) methods were used to create high-resolution images of underground cave. The result of ERT and geological survey was used as an entry model for the gravity modelling. The most important results from ERT and microgravity are two interpreted low density (low resistivity) structures - these can be important from the point of view of karst structures investigation.

Euler deconvolution is one of the best developed methods for semi-automated interpretation of potential fields in the last two decades. This paper describes a two steps procedure based on: the stabilization of the input derivatives by regularization (1.step) and involving the regularized solution of the linear equation system (included in a 2.step). This can significantly improve the Euler deconvolution (ED) method which leads to better interpretations of potential fields. In this study the two steps stabilization approach will be applied to a synthetic model and a real data set which stems from an archaeological microgravity survey. These two case studies were calculated by the classical ED and the new derivative ED methods (DED). The latter is a modification of the classical approach and bases on initial vertical derivative evaluation for input data and it results in a direct estimate of structural index values. Presented new two steps procedure provides better estimations of Euler depths and eliminates significantly false solutions.

Downward continuation of potential fields is an important tool in their interpretation - depths of shallowest important sources can be determined by means of stable downward continuation algorithms. In this contribution we analyse the properties of one from these algorithms (based on Tikhonov's regularization approach) from the scope of two most important discretization parameters - dimensions of the areal coverage of the interpreted field and the sampling interval size. We show on one synthetic body (sphere) and one real-world data-set (results from a microgravity survey for cavities detection) that there is a need for a relatively large surroundings around the interpreted anomaly. Beside of this also the sampling step plays its important role - grids with finer sampling steps give better interpretation results, when using this method. From this point of view, this method is more suitable for the interpretation of objects in near surface and mining geophysics (anomalies from cavities, unexploded ordnance objects and ore bodies).

One of major environmental challenges in Slovakia is to deal with numerous contaminated sites polluted by improper waste management in the past. We present a case study from Babica landfill located in western part of Slovakia near the village Bosany. The landfill was established in 1970, in a very inappropriate environment of abandoned meander. Waste composition of the Babica landfill is mainly formed by waste from the leather and footwear production. Broad spectrum of geophysical methods were applied on several profiles in order to describe the spatial limitation of landfill materials and to monitor the spread of contamination from the landfill in the surrounding environment. Combination of several geoelectrical methods (EMI, ERT, VES and SP) allows us to define the resistivity model of the area, where the contaminated area was clearly outlined by low resistivity values. Moreover VES measurements were sorted in four elementary classes defined by the shape of the VES curve, which allows us to create schematic model of the area. Self-Potential method proved the active connection of the abandoned meander with the river. Additionally, soil vapour method survey revealed three outbreaks of methane gas generation that are connected to the area near the old meander.

A powerful toll in the estimation of potential field source depths is given by the analytical downward continuation of the measured field - down to the depth of the first important shallow sources. On the other hand, analytical downward continuation is an highly instable problem and one effective way for its solution is Tikhonov regularization. Combination with the Derivative Euler Deconvolution can effectively help in the estimation of the depths to the centres of researched near-surface microgravity anomaly sources. This was presented on one selected synthetic model studies and one real data application. In some situations the estimations from Euler deconvolution are deeper, in some shallower, on the present we are not able to explain this aspect. Experiences with the regularized downward continuation show its very low dependence on grid extent and the grid cells sizes. Derivative Euler Deconvolution has showed large sensitivity to the precise evaluation of the initial vertical derivative – it has to be smoothed or damped in the case of real data interpretation (where noise and acquisition errors are present).