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Verification, analysis and interpretation of gravity anomaly at locality Žírovice in the Cheb Basin
Vaško, Oskar ; Mrlina, Jan (advisor) ; Blecha, Vratislav (referee)
In the vicinity of the Žírovice village near Františkovy Lázně in West Bohemia there exists a striking gravimetric isometric negative anomaly. Similar gravimetric anomaly near Mýtina, about 17 km to the SE of Žírovice, was interpreted by Mrlina et al. (2009) as a Quaternary volcanic structure of a maar-diatreme type. It is possible that the Žírovice anomaly and some other similar anomalies in the Cheb Basin may also reflect Tertiary or Quaternary volcanic structures. For this reason we performed a detailed gravimetric and magnetometric survey, followed by geophysical modeling. The presence of a volcanic structure was not confirmed by this work, on the contrary, it was rather excluded. The anomaly was interpreted as a sunken tectonic 3D block/graben.
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Temporal gravity changes related to geodynamic phenomena and geomechanical processes
Mrlina, Jan ; Blecha, Vratislav (advisor) ; Novotný, Oldřich (referee) ; Pašteka, Roman (referee)
My Thesis is based on five papers dealing with gravity changes related to various geodynamic, geomechanical and hydrological processes and phenomena. In the first part of the Thesis the gravity changes are defined as a geophysical quantity. The two principal causative parameters are highlighted - variation in elevation of the earth surface, and temporal excess of mass (negative or positive) in the subsurface. I also discuss different groups of parameters and environmental phenomena disturbing the gravity measurements, as the data accuracy is an essential condition of gravity monitoring (4D gravity). I performed a special test with the LaCoste&Romberg D-188 gravimeter in a pressure chamber with notable result showing negligible impact of small and medium size air-pressure variations on this instrument. The calibration stability was proved during two world comparison/calibration campaigns of absolute and relative gravimeters in Sevres, France. The instrument's repeatability was evaluated as 2 μGal (0.02 μm/s 2 ). As well, calibration is being controlled by measurements on the Czech latitude calibration line between Prague and Dolní Dvořiště in South Bohemia. In order to achieve best accuracy we developed special software Drift to control the gravimeter's drift. In principle the software provides a...
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Gravity survey of the highway route D3
Kohout, Milan ; Blecha, Vratislav (advisor) ; Mrlina, Jan (referee)
The aim of this thesis was to determine if in the area lying west of the town Jílové u Prahy occur old mine galleries, that could pose a risk for the future construction of the highway D3. The problem was solved by microgravity measurements carried out in an area of 310 x 50 m on the five profiles. There were 3 parallel profiles P15, P1 and P-15 and 2 profiles P9290 and 9180 which were perpendicular to them. The measured data were then quantitatively and qualitatively interpreted in the programs Surfer and GM-SYS. The survey located four areas of potential occurrence of galleries or tectonics lines that also appear in the area of study. Quantitative interpretation excluded the presence of the galleries in three sections. In one area was not possible to recognize if the negative anomaly in caused by old mine gallery or by the fault. Based on the interpreted data there was marked one potential risk area with possible occurrence of the old mine gallery. For more accurate information it would be necessary to make more detailed microgravity survey supplemented by electrical resistivity tomography.
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Microgravity survey and monitoring of subsurface inhomogeneities
Spěšný, Marek ; Mrlina, Jan (advisor) ; Blecha, Vratislav (referee)
Marek Spěšný - abstract This thesis has the nature of a survey report of a specific area. The task was to localize with the help of microgravimetry anomalous places in an area of a by-pass road construction, where subsurface inhomogeneities may possibly exist due to subsurface and surface historical mining of ceramic clay. The gravimetrical measurements were carried out with a relative gravimeter Scintrex model CG-5 AUTOGRAV. After the first stage of the gravimetrical measurements and following two weeks of recultivation works our assignment was to verify the success of the first measurements by the means of repeated microgravimetric control measurements. The results from both stages of measurement were processed into a 4D gravimetrical form. The results of the 4D gravimetry displayed that contrary to the expectations, the measured gravity of most of the area of interest decreased as much as by 30 ?Gal. We conclude that this is due to the drainage of injected material beyond the recultivated mining area, which washed and carried away a portion of the existing material. Our proposition was also supported by results of repeated leveling, which discovered subsidence of the road at times by up to 3 centimeters.
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Dynamics of Earth gases emissions in Czechia
Kroufek, J. ; Stejskal, M. ; Šebor, G. ; Mrlina, Jan ; Tesař, J. ; Suchý, V. ; Zeman, A.
A monitoring of the Earth gases emissions was carried out at selected sites in Cechia. Particularly, methan, CO2, SO2, Rn a H2S were investigated. It was proved that neither the chemical composition, nor the emissions themselves can be considered as permanent. They may be affected by geological processes including earthquakes, as well as by man-made activities.
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