Since 1998, a seismic network has been monitoring the underground gas storage located near the town of Příbram in the Central Bohemian Pluton, Czech Republic. Hundreds of weak induced seismic events have been recorded there. Moreover, several weak earthquakes have also been recorded from the vicinity of the nearby Orlík water reservoir. To improve location of both types of seismic events, shallow crustal structure of the region is studied in the present paper. Refraction measurements to distances of about 20 km were carried out using quarry blasts as seismic sources. Smoothed P-wave travel times were interpreted using the Wiechert-Herglotz method, which yielded a 1-D velocity model of shallow crustal structure down to a depth of about 1.7 km. The P-wave velocity of the model increases from about 5.0 km/s at the surface to about 6.15 km/s at the 1.7 km depth., Jiří Málek, Oldřich Novotný and Libor Žanda., and Obsahuje bibliografii
Among the programmes aimed at developing a standard model for properties and state of the Earth’s crystalline crust, those dealing with drilling the Kola (SG-3), Ural (SG-4) and German (KTB) superdeep boreholes yielded the most interesting results. No marked depth dependence of rock volume density and seismic wave velocities was observed in the sections of SG-3 and SG-4. A new result of the investigations is the discovery of strongly anisotropic rocks in the SG-3, SG-4 and KTB sections. In the massifs of the Kola and German superdeep boreholes such rocks constitute the majority of the drilled sections. The presence of the velocity anisotropy as well as the complex structure of the rocks composing crystalline metamorphosed sequences greatly hamper the interpretation of the results obtained from the seismic survey conducted at the surface., Felix F. Gobratsevich., and Obsahuje bibliografii
In our study we find, from the analysis of VLBI observations, small quasi-periodic fluctuations of the period and quality factor of retrograde Free Core Nutation (FCN), ranging mainly between 429.8 to 430.8 days and 17000 to 21000, respectively. To this end, we use resonant effects in several dominant forced nutation terms to calculate the period and quality factor of FCN in running 6-year intervals. We also recently demonstrated that the atmospheric and oceanic excitations are capable of exciting FCN. Both amplitude and phase of the geophysically excited motion are consistent with the values observed by VLBI, in the interval of tens of years. The geophysical excitations are now numerically integrated, using Brzeziński’s broadband Liouville equations, and removed from the observed celestial pole offsets. The remaining part is then used to derive the period and quality factor of FCN in running intervals, and to study the temporal stability of these important Earth parameters. It is demonstrated that the observed quasi-periodic variations of both parameters are probably not caused by these geophysical excitations., Jan Vondrák and Cyril Ron., and Obsahuje bibliografii
The results obtained by four years long TM 71 extensometer monitoring of 3D micro-tectonic displacements of Dinaric Fault Zone on two sites, being 260 m apart in Postojna Cave, were statistically evaluated with different methods (Kolmogorov- Smirnov test, comparison between relative displacement and earthquakes, linear regression, Kruskal-Wallis one-way analysis of variance, histograms and correlation coefficients). Responses to stress changes regarding x, y and z-axes are not the same on two monitoring sites even if we are monitoring the same fault zone. Kolmogorov-Smirnov test for comparing the two curves is applicable only for three axes combination (Postojna 1 z - Postojna 2 z, Postojna 2 y - Postojna 1 z, and Postojna 2 z - Postojna 2 y). Kruskal-Wallis analysis is most representative for z-axes. Some sharp peaks coincide with earthquake occurrences (Krn M=5.2, Cerkno M=4.0, Ilirska Bistrica M=3.9, Brežice M=2.9 and Krško M=3.1). Generally we detect very small tectonic deformations, dextral horizontal movement of 0.05 mm in 4 years for Postojna 1 and extension of 0.03 mm in 4 years for Postojna 2. Discrepancies between two sites can be attributed to complex geological structure and by the fact that studied fault zone is cut by cross-Dinaric fault zone., Stanka Šebela, Janez Turk, Janez Mulec, Blahoslav Košťák and Josef Stemberk., and Obsahuje bibliografii
Integration between magnetic and gravity data at the Zelten platform, the southeast part of Sirt Basin Libya. Zelten Platform is first discovered oil field in Libya. It shows numerous geological structures of different tectonic events. The methods adopted can assist in locating the hidden subsurface structures. The platform is characterized by the NW-SE trending rift that belongs to the Early Cretaceous age (during the collapse of Sirt Arch). The study aimed to define the structural geology that assisted in the development of future exploration in this area. The analyses utilized several filtering and transformation algorithms to help in structural modeling. For instance, the total horizontal gradient and tilt angle derivative were applied for the edge detection of the tectonic boundaries. The results show NW-SE and NNW-SSE patterns that represents faults that controlled the positions of the troughs and platforms at the Sirt basin. On the other hand, Euler deconvolution and 2D forward modeling were utilized to determine the depth of the basement. The Integrated models deduced revealed that the main faults trends are NW-SE which refer to the rift phases and crustal extension period that occurred during the Mesozoic time (early cretaceous). Also, the basement depth ranges from 6.5 km to 8 km according to the structures that affected the study area., Abdelhakim Eshanibli, Amin Khalil, Abdellatif Younis and Hussin Ghanoush., and Obsahuje bibliografii
This paper presents the subject related to the technology of creating fractures into a rock, as well as the subject related to the effect of the proppant embedment phenomenon on the effective packed fracture in a reservoir rock. This phenomenon occurs after the performed hydraulic fracturing treatment of hydrocarbon reservoirs, during closing of the rock mass. A key part of this experiment was to investigate the depth of proppant grains penetration into the fracture wall (shale rock) and size of damage to the fracture wall surface. The embedment phenomena effects on decrease in the width fracture packed with proppant. The tests were performed for shale rock initially soaked with fracturing fluid, lightweight ceramic proppant grains with a grain size of 0.600÷0.300 mm (medium diameter of proppant grains of 0.450 mm), low surface concentration of proppant of 2.44 kg/m2. Time of exposure of proppant grains to compressive stress of a value 48.3 MPa for 6 hours at 70 oC. Test results indicate that the developed testing methodology may be used for corrected evaluation of the fracturing fluid as well as proppant in hydraulic fracturing treatment of unconventional reservoirs, especially shale rocks. and Maslowski Mateusz, Kasza Piotr, Wilk Klaudia.
To obtain the starting point for theoretical numerical computations the fibre reinforced concrete construction properties, adhesion of cement mixture with steel and polypropylene fibres and changes in its tension properties commensurate with number and weight percentage in the tested specimen were tested under laboratory conditions., Jiřina Trčková and Karel Řezba., and Obsahuje bibliografické odkazy
Evaluation of seismic loading in urban areas is not a simple process. The horizontal to vertical spectral ratio method technique has been often used for determination of site effect recently. Results from the re-interpretation of mining induced seismic events from Karviná region in frequency domain using archival databases will be presented in this study material. Also, spectra of continuous records (a bout two days) and evolution of spectra within a moving time window of the length 10 seconds are presented. These continuous records were registered on two places with different geological conditions., Zdeněk Kaláb and Alexey A. Lyubushin., and Obsahuje bibliografické odkazy
Generally, rock material failure is controlled by cracks under specific conditions. The study of rock fracture toughness belongs to the current frequent directions of research in the area of rock failure. The present paper describes the effects of parameters influencing the resultant properties of rock materials (bending rate, rock moisture) during fracture toughness measurement of different kinds of rocks (sandstone, marble, granite). The highest fracture toughness values were found in the marble samples. This is probably due to the inner structure of analysed marble, which is composed of only one mineral (calcite) and also has a lower porosity than the used granite. The lowest fracture toughness values were found in the sandstone sample, and reached c. 17-30 % of the measured fracture toughness values of the analysed granite and marble samples. As in the case of the other mechanical properties of rocks (e.g. uniaxial compressive strength) also in the case of higher sandstone (carboniferous) moisture the fracture toughness values decrease and its deformation ability increases. Preparation of samples for fracture toughness tests and performance of these tests are more complicated than in the case of tensile tests (e.g. the Brazilian test) and therefore this contribution presents a comparison between fracture toughness of analysed rocks and tensile strength values. The measured data in this study considering the fracture toughness tests and Brazilian tests were compared with results published by Zhang (2002)., Leona Vavro and Kamil Souček., and Obsahuje bibliografii