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Journal Acta Geophysica vol.60,no.2
Subject: Geology Type: Journal

Author: Janusz Bogusz and Mariusz Figurski, Hakim Saibi, Essam Aboud and Sachio Ehara, Giuliana Verbanac and Eugen Vuji?, Mario Mustasaar, Juri Plado and Argo J?eleht, Mih?ly Dobr?ka and Judit Somogyi Moln?r, Wojciech D?bski, Sylwia Tomecka-Sucho?, Zden?k Kal?b and Marketa Lednick?, Aneta Golik and Maciej Jan Mendecki, Zden?k Kal?b, Marketa Lednick?, Robert Ko??nek and Eva Hrube?ov?, Stanis?aw R. ?miel, Krystyna Stec and Jan Drzewiecki, Jerzy Kornowski and Joanna Kurzeja, Karel Holub, Bohuslav R??ek and Jana Ru?ajov?

Publication Date: April 2012  Publication No: vol.60,no.2Pages Number: 

GPS-derived height changes in diurnal and sub-diurnal timescales
   This paper describes the research concerning precise short-time GPS solutions conducted in the Centre of Applied Geomatics, Military University of Technology, Warsaw, Poland. The data from ASG-EUPOS (Polish Active Geodetic Network) was processed using Bernese 5.0 software and EPN (EUREF Permanent Network) standards and models. In this study, the adapted 3-hour observation window is shifted every hour for obtaining hourly geocentric coordinates in ITRF2005 reference frame. The adjusted network consisted of over 130 stations from Poland and the neighbouring countries, the period covered observations collected from June 2008 through June 2010. These two years of observations allowed for examining short-period oscillations which were found to be closely related to the tidal (dynamic) frequencies. The analysis of the residua from the IERS2003 tidal model was performed using the least squares method with the Eterna software. It confirmed the existence of significant (several millimetres) oscillations in the frequencies corresponding to S1, K1 and K2. The paper describes the idea of data processing and analysis, presents the results of vertical (the Up component) oscillations in main tidal frequency bands, and also includes discussion of possible explanation of the existence of short-period oscillations in the GPS precise solutions and the possibility of propagation of short-period oscillations into long-period spurious changes in the daily (standard) GPS solutions.
   Analysis and interpretation of gravity data from the Aluto-Langano geothermal field of Ethiopia
   The Aluto-Langano geothermal field is located in the central southern portion of Ethiopia within the Ethiopian Rift Valley. The gravity of the area was surveyed in an attempt to delineate the subsurface structure and to better understand the relationship between the geothermal systems and the subsurface structure. The gravity data were analyzed using integrated gradient interpretation techniques, such as the Horizontal Gradient (HG), Source Edge Detection (SED), and Euler Deconvolution (ED) methods. These techniques detected many faults that were compared with the mapped faults in the surface geology. The results of the present study will lead to an improved understanding of the geothermal system in the study area and aid the future geothermal exploration of the area.
   Determination of the Croatian geomagnetic observatory location
   Ground survey within the Nature Park Lonjsko Polje, placed in the middle-northern Croatia was performed during the time interval 2007-2010 in order to find the best location for installing the geomagnetic observatory. The total magnetic field has been measured a few times using the Overhauser proton magnetometers. The horizontal and vertical gradients of the total field, and its temporal behaviour were investigated over the restricted region that we estimated as suitable for the observatory. The results obtained from thoroughly conducted measurements allowed us to find definitive positions for the instrument pillars. These results are in agreement with previously suggested location found based on combination of Comprehensive CM4 model prediction and measurements conducted from 2003 to 2005. This study contributes to the development of geomagnetism in Croatia and paves a way to install the first geomagnetic observatory in Croatia.
   Determination of electromagnetic wave velocity in horizontally layered sedimentary target: A ground-penetrating radar study from Silurian limestones, Estonia
   Ground-penetrating radar (GPR) is a non-destructive geophysical technique to obtain information about shallow subsurface by transmitting electromagnetic waves into the ground and registering signals reflected from objects or layers with different dielectric properties. The present GPR study was conducted in Vohmuta limestone quarry in Estonia in order to describe the relationship between GRP responses to the variations in petrophysical properties. Sub-horizontally oriented cores for petrophysical measurements were drilled from the side wall of the quarry. The GPR profiles were run at the sloped trench floor and on the top of side wall in order to correlate traceable reflections with physical properties. Based on three techniques: (i) hyperbola fitting, (ii) wide angle reflection and refraction (WARR), and (iii) topographic, a mean electromagnetic wave velocity value of 9.25 cm ns-1 (corresponding to relative dielectric permittivity of 10.5) was found to describe the sequence and was used for time-to-depth conversion. Examination of radar images against petrophysical properties revealed that major reflections appear in levels where the changes in porosity occur.
   New petrophysical model describing the pressure dependence of seismic velocity
   Seismic data are increasingly applied to predict the characteristics of reservoirs, as their quality improves. Since the change of pressure is a major component in exploitation of reservoirs, a thorough understanding of the influence of pressure on seismic velocity is also important. In this study we introduce the first results of the developed petrophysical model which describes the pressure dependence of seismic velocity. The model is based on the idea that microcracks in rocks open and close under the change of pressure. Laboratory measurements are presented on several sandstone samples. Longitudinal wave velocities were measured at various incremental pressures increased from 0 to 20 MPa. During the measurements, the pulse transmission technique was used and the parameters of the model were determined by using a linearized inversion method. The inversion results proved that the proposed petrophysical model well applies in practice.
   Georadar studies on St. Benedict s Church on Lasota Hill, Krakow, Poland
   Georadar methodology has a considerable potential as a tool for verification of archeological hypotheses. I applied it in the present study to resolve a discussion on the importance of a Proto-Romanesque structure located on Lasota Hill. It is one of the oldest structures on the right bank of Vistula River in Krakow in Poland and some archeologists believe that it was the first seat of the rulers of Lesser Poland in the 9th century. After few decades, the prince s castle was built on Wawel Hill, where subsequently the royal castle was constructed. On the place of the abandoned Proto-Romanesque edifice, a small St. Benedict s Church was raised, but the importance of its predecessor was discussed. Archeological excavations suggested that it served as the prince s residence, but this view would be much strengthened if traces of a prince s building - palatium - could be found. With this in mind, I undertook a search for traces of palatium, employing georadar methodology. I carried out the measurements using Georadar PROEX produced by MALA Geoscience with a set of shielded antennas of frequencies 500 and 800 MHz. They permitted to construct echogram profiles, whose interpretation suggested the existence of palatium. Thus, the georadar data supported the archeological hypothesis about the important role of the Proto-Romanesque structures on Lasota Hill in the early medieval era in Poland, and at the same time demonstrated the usefulness of introducing geophysical methods to archaeology.
   Foundation conditions of buildings in undermined areas: An example of evaluation
   Evaluation of a set of individual geological and petrophysical parameters is necessary in many geoscientific studies or those with constructional purposes. However, correlation and mutual evaluation of these parameters are very complicated. Our methodology, which is part of the expert evaluation, is based on compilation of four significant effects: local subsurface geology, groundwater table (and accumulation of surface water), deformation of the surface due to mining (subsidence), and landslides. Different values of specified significances were assigned to all four selected effects. The class of foundation conditions was selected according to the summary of values of specified significances for a given point. This value describes how the selected parameters influence vibration effect on the surface and resistance of buildings to this seismic loading. The pilot map of foundation conditions, which was elaborated as part of the evaluation of Stonava area in 2008, is presented.
   Ground-motion prediction equations for induced seismicity in the main anticline and main syncline, Upper Silesian Coal Basin, Poland
   The purpose of the research was to determine parameters of ground-motion models for two areas characterized by considerable induced seismicity and different geology. Fifty-nine events collected from surface seismological stations of coal mine (Bielszowice) (at the Main Anticline, South Poland) and 144 events from coal mine (Ziemowit) (at the Main Syncline, South Poland) were used for computation. For both areas, simple ground-motion prediction equations (GMPEs) without site effects were derived, but the model was acceptable only for (Bielszowice) area. The GMPE was calculated once again for (Ziemowit), but this time we took into consideration the amplification coefficient, which significantly improved the model solution. Finally, the theoretical value of amplification was calculated. Knowing that the amplification is associated with subsurface layers, we used three different models of overburden: (i) with Quaternary sediments only, (ii) with a complex of Quaternary-Tertiary sediments, and (iii) with a complex of Quaternary-Tertiary-Triassic sediments and Carboniferous as a basement. Usually, the amplification of vibrations appears in the Quaternary sediments. However, theoretical calculations of amplification were consistent with the results obtained from GMPE when a rigid Carboniferous substratum was applied.
   Influence of local geological pattern on values of vibrations induced by road traffic
   Buildings in the proximity of roads can be affected by vibrations induced by traffic. Local geological pattern is necessary to be taken into account because it has significant influence on values of vibrations and their characteristics. This paper summarizes results of experimental measurements. Four different types of buildings in different types of local geology were used for this purpose. The obtained results document that the generation of significant vibrations is mostly due to heavy vehicles. Some maximum velocity values exceed acceptable limits according to the Czech Technical Standard 73 0040 for evaluation of technical seismicity effect on buildings. Cosmetic damage, meaning the cracking of plaster, might occur due to traffic vibrations.
   Relations between coal transformation and geometric features of faults in the Upper Silesian Coal Basin
   The paper presents the results of studies of fault zones carried out in the Upper Silesian Coal Basin. Three types of changes of the coal were distinguished: degradative changes connected with a deterioration in the quality of the coal; aggradational changes connected with an increase in the quality of coal; and the type of coal which shows no significant change in the values of its parameters.
   Hypergenic changes of the coal were mainly observed in the fissures of faults with the dominant strike in NW-SE and NE-SW directions. The faults of such parameters in the USCB are characterized as fragile. They were formed in the period of the inversion of the USCB, in a tensional stress regime. Aggrading changes of coal were observed in the faults planes with the dominant strike in NNW-SSE and W-E directions. The faults of such a run in the USCB are susceptible in nature and developed during the compressive regime. In the fault zones where no changes were in the coal quality, the orientation of faulting surfaces did not show the privileged run direction.
   Mine tremor focal mechanism: An essential element for recognising the process of mine working destruction
   This article presents an analysis of causes of rockburst which occurred in the Rydultowy-Anna Mine on 24 March 2010. The seismic phenomena and the rockburst hazard connected with them have been determined by a number of natural and technical factors. The dominant factors were the mechanical strength characteristics of coal and surrounding rocks, as well as the values of stress in the surroundings of mine workings. An analysis must take into account the structure of the strata, its susceptibility to rockbursts, development and displacement of areas with high values of stress, as well as critical levels of elastic deformation of the strata. Such an approach must be supported by the results of an analysis of focal mechanisms of tremors to make it possible to recognize mining and geological factors which had the prevailing influence on tremors location and energy. By presenting a selected example of a real event, the authors would like to point out the importance of the proper description of focal mechanisms of seismic tremors. The analysis of a chain of interacting destruction processes in the developed model of strata would give the explanation why the tremor occurred in the gallery located at a considerable distance from the tremor focus.
   Prediction of rockburst probability given seismic energy and factors defined by the expert method of hazard evaluation (MRG)
   In this paper we suggest that conditional estimator/predictor of rockburst probability (and rockburst hazard, P T (t)) can be approximated with the formula P T (t) = P 1(? 1)P N (? N )P dyn T (t), where P dyn T (t) is a time-dependent probability of rockburst given only the predicted seismic energy parameters, while P i (? i ) are amplifying coefficients due to local geologic and mining conditions, as defined by the Expert Method of (rockburst) Hazard Evaluation (MRG) known in the Polish mining industry. All the elements of the formula are (approximately) calculable (on-line) and the resulting P T value satisfies inequalities 0 = P T (t) = 1. As a result, the hazard space (0-1) can be always divided into smaller subspaces (e.g., 0-10-5, 10-5-10-4, 10-4-10-3, 10-3-1), possibly named with symbols (e.g., A, B, C, D, ...) called (hazard states) - which saves the prediction users from worrying of probabilities. The estimator P T can be interpreted as a formal statement of (reformulated) Comprehensive Method of Rockburst State of Hazard Evaluation, well known in Polish mining industry. The estimator P T is natural, logically consistent and physically interpretable. Due to full formalization, it can be easily generalized, incorporating relevant information from other sources/methods.
   A simple smoothed velocity model of the uppermost Earth s crust derived from joint inversion of Pg and Sg waves
   The paper presents some results of seismic experiments carried out on the territory of northern Moravia and Silesia, roughly delimited by the coordinates 16 degrees E-19 degrees E and 49 degrees N-51 degrees N. The experiments were aimed at compiling a velocity model of the uppermost Earth s crust using the database of arrival times of Pg and Sg waves recorded at a fairly large number of seismic stations, which enabled us to produce a simple 1D-layered velocity model of the region. The velocity model was computed using the traditional tomographic iterative process composed of consecutive solutions of linear equations. Based on the analysis of velocity distribution, it was found that the velocities of Pg and Sg waves increase from about 5.9 and 3.3 km/s at the surface, to about 6.1 and 3.5 km/s at a depth of 11 km, respectively.

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