Andrej Mojzeš

Pliocene to Quaternary tectonics in the Horná Nitra Depression (Western Carpathians)

Pliocene to Quaternary tectonics in the Horná Nitra Depression (Western Carpathians) The Horná Nitra Depression is an Upper Miocene-Quaternary intramontane sedimentary basin. This N-S elongated 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 SH and perpendicular minimum horizontal compressional stress Sh 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.

The resistivity image of the Muráň fault zone (Central Western Carpathians) obtained by electrical resistivity tomography

The resistivity image of the Muráň fault zone (Central Western Carpathians) obtained by electrical resistivity tomography The paper describes the application of geophysical prospecting techniques for estimation of the faults inclination. The field survey was carried out across the Muráň fault structure in the Slovenské rudohorie Mts (central Slovakia). Three different geophysical methods were used to map the fault zone: Electrical Resistivity Tomography (ERT), induced polarization (IP) and radon emanometry. All these methods have been used to locate the fault zone area, but the principal aims of this research are to test the efficiency of the 2D ERT technique to recognize the geometrical characterization of the fault and to improve our tectonic knowledge of the investigated area. For the synthetic cases, three geometric contexts were modelled at 60, 90 and 120 degrees and computed with the l2 norm inversion method, the l1 norm with standard horizontal and vertical roughness filter and the l1 norm with diagonal roughness filter. In the second phase this geophysical methodology was applied to fieldwork data. Our results confirm that the ERT technique is a valuable tool to image the fault zone and to characterize the general geometry, but also the importance of setting up the right inversion parameters. The main contribution of the geophysical investigations in this case was the determination of the location and confirmation of the inclination of the Muráň fault. The result of this study is the ability to make a visual estimation of the direction and dip of the fault. Pursuant to this work the dipole-dipole electrode configuration produces the best resolution, particularly for the location of vertical and dipping structures. The advantage of this array is that it shows the ability to assess the trend of the dip and therefore it can be strongly recommended. The result is also a case study of a small scale tectonic survey involving geophysical methods.

Complex geophysical investigation of the Kapušany landslide (Eastern Slovakia)

Abstract Geophysical survey is a very useful and popular tool used by engineering geologists to examine landslides. We present a case study from the Kapušany landslide, Eastern Slovakia, where a broad spectrum of geophysical methods were applied along two perpendicular profiles in order to compare the ability of the methods to detect as many structural features of the landslide as possible. The 2D Electrical Resistivity Tomography inverse model was capable of defining the geological structure of the landslide and defining the shear zone, however the resolution of the inverse model does not allow us to identify cracks or other minor features of the landslide. These, however, were well recorded in the results of Dipole Electromagnetic Imaging and the Self Potential method. In addition microgravimetry, Gamma-Ray Spectrometry and Soil Radon Emanometry were experimentally employed to validate the results obtained from electrical methods and afterwards final geological models, based on the integrated interpretation of all involved methods were constructed.

Results of the gravity field interpretation in the Turčianska Kotlina Basin

Results of the gravity field interpretation in the Turčianska Kotlina Basin The paper deals with the quantitative interpretation of the gravity field in the Turčianska Kotlina Basin. The interpretation was done by means of the application of the 2D density modelling method using the GM-SYS software. Geophysical constraints of the density models are represented by the existing geophysical measurements and interpretations. The Turčianska Kotlina Basin in the picture of the regional gravity field is characterized by the local gravity low with amplitude of about 12 mGal. The source of this gravity low is low density Tertiary sediments, which fill the basin. From the Tertiary sediments the Neogene sediments play dominant role in observed gravity, because their gravity effects are considerably larger in comparison with the gravity effects of the Paleogene sediments. The contacts between the Malá Fatra and Veľká Fatra Mts., and the Turčianska Kotlina Basin are characterized by the significant gravity gradients. They reflect tectonic contact between the basin and crystalline core mountains. In the Turčianska gravity low we can see along the Profile TK-AL three local gravity lows. The highest local gravity low is explained by the largest thickness of the Tertiary sediments. Another two local gravity lows are also characterised by thicker layers of the Tertiary sediments. Density models assume that the eastern (western) part of the basin basement is built by the Mesozoic (crystalline) rocks. In the central part of the Profile TK-BL the thick Paleogene sedimentary filling (more than 1 km) compensates the deepest part of the Pretertiary basement. Density model along the Profile TK-BL does not suggest a presence of the Paleogene sediments in the basin filling. It is also indicated that the Mesozoic rocks underlie the Tertiary sediments. The Pretertiary basement was interpreted in the depths from 0 km up to the 2 km. Note that all geological structures (blocks) are sliding from the East to the West. The dipping of the Malá Fatra Mts. is steeper than in a case of the Veľká Fatra Mts. The anomalous bodies observed on the western part of the basin result from the alluvial and detrital cones. Their presence and gravity effect can be observed mainly on the eastern slope of the Malá Fatra Mts.

Radon measurements in an area of tectonic zone: A case study in Central Slovakia

General overviews of the spatial distribution of radon and other natural radionuclides in the geological basement as commonly presented on regional or country maps tend to offer a low density of information, insufficient for gaining relevant knowledge of the environmental impact, especially in the areas of tectonic zones often assumed to be radon prone and therefore dangerous for the human population. An additional survey, employing radon measurements in soil and indoor air, was carried out seeking to provide a more detailed characterization of the expressive fault zone of the Malá Magura in the Horná Nitra region of Central Slovakia. Eventually, the results of soil 222Rn volume activity measurements along two short profiles crossing the assumed fault line did not reveal any indication of active nature of local tectonics, but merely pointed to an existence of a zone of contact between different types of rocks. The results of indoor radon measurements in dwellings of two villages lying on the studied fault showed values that were lower than those commonly observed on the Slovak territory, ruling out any negative health impact on population. Nevertheless, in order to add new findings to an already well established study of geological structure of the region, the indoor radon data collected through a previous survey require a further analysis.

Investigation in Sinkhole Terrains Using Complex of Geophysical Methods – Case Study in the Karst Area, Slovakia

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.

Linearization of the Sobolev and Babeyko's formulae for transformation of P-wave velocity to density in the Carpathian-Pannonian Basin region

Linearization of the Sobolev and Babeykos formulae for transformation of P-wave velocity to density in the Carpathian-Pannonian Basin region The initial density model has to be based on a reasonable geological hypothesis and while the modelling process is non-unique, one of the interpretation aims is to define the robust parameters of the model. It is important at this stage to integrate the seismic and gravity data. One of the possibilities how to integrate these data is transformation of the seismic velocities to densities. The Sobolev and Babeykos formulae belong to the most available relationships for this transformation. They are very complex and rigorous taking into account the PT conditions. On the other hand its application is relatively complicated. Therefore the main goal of the paper is to try to determine more easily the formula for transformation of the seismic velocities to densities. Based on the analysis of the results obtained using the Sobolev and Babeykos formula on real data, we found out that in the Carpathian-Pannonian Basin region this formula can be transformed to simpler linear velocity-density relationship with required accuracy.