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Joint interpretations of geophysical measurements as the key to understand landscape evolution
Tábořík, Petr ; Fischer, Tomáš (advisor) ; Kněz, Jaroslav (referee) ; Putiška, René (referee)
Užitá geofyzika představuje rychlý, efektivní a nedestruktivní způsob získávání informací o složení a stavu horninového prostředí, jakož i o studovaných geologických či geomorfologických procesech. Kombinování různých metod geofyzikálního průzkumu přináší ve srovnání s použitím pouze jedné geofyzikální metody výrazně širší rozsah měřených fyzikálních parametrů, což umožňuje získání mnohem podrobnějších informací o zkoumaném geologickém prostředí. K interpretacím geofyzikálních dat je vždy potřeba přistupovat obezřetně, protože jde mnohdy jen o jedno z pravděpodobných, nikoli však jediných možných řešení. Předkládaná disertační práce na několika vybraných případech ilustruje, jak snadno může dojít k nepřesné, nebo dokonce mylné interpretaci. V řadě případů přitom nemusí jít o problém kvality dat nebo chybného nastavení parametrů výpočetního modelu. Problém nastává při interpretaci výsledků, kdy dochází k přiřazení určité geologické kvality ke konkrétní měřené nebo modelované hodnotě nebo pozorované anomálii. Sdružené interpretace geofyzikálních metod (ideálně doplněné informacemi "negeofyzikálního" charakteru) mohou nejen přinést zásadní informace o studovaných geologických či geomorfologických fenoménech, ale také přispět metodickými poznatky, a to jak k metodám jednotlivým, tak zejména k jejich...
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Geophysical survey of subsurface voids at locality Letonice
Bartášková, Lucie ; Blecha, Vratislav (advisor) ; Skácelová, Zuzana (referee)
The Větrníky national nature reserve, located in the South Moravian region north of the village of Letonice, is one of the largest steppe reserves in Southern Moravia. This whole area is characterized by the presence of both stable and active landslides, and the occurrence of suffosion sinkholes has been monitored there in the long-term. The aim of the thesis was to investigate whether it was possible to observe subsurface phenomena, caused by the washing out of fine rock particles by ground water, by means of geophysical methods. This phenomenon is known as suffosion. The measurements took place in the areas where the suffosion manifestation was very distinctive, that is around two sinkholes that were visible on the surface. In order to identify the suffosion structural-geological causes and their manifestations at a given location, the gravimetric and electrical resistivity tomography (ERT) methods were used in the first stage of the research. Measured data was further processed and geologically interpreted. The gravimetric method has proved suitable when identifying rocks affected by suffosion, in which case we assume that their density is lower than the density of the surrounding rocks. Using the ERT method, it was possible, in the vertical profile, to distinguish the sandy-gravelly sediments...
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Geophysical survey of undermined area in Lukavice near Chrudim
Slavíčková, Michaela ; Blecha, Vratislav (advisor) ; Dohnal, Jiří (referee)
Lukavice village is located in Eastern Bohemia and it is known for its historical pyrite mining. The first mention of mining comes from the beginning of 17th century. The mines were abandoned in 1892 due to a significant depletion of the upper parts of the deposit and also because of the competition of cheaper pyrite from abroad. Old mine workings were often backfilled incompletely and their exact location is unknown. The occurrence of empty mine workings under the roads in the village centre could cause a collapse of the ground under the weight of heavy trucks which carry through Lukavice village aggregate from the nearby quarry. The aim of geophysics was to determine the thickness of dump material (seismics), subsidence monitoring in the village centre (repeated levelling) and the principal aim was to locate old mine galleries and shafts (gravity survey). Gravity measurements did not prove the presence of empty mine workings under the main road at the village centre. Most pronounced negative Bouguer anomaly, which occurs in the vicinity of Bartolomějská jáma schaft, may be caused by higher degree of alteration of underlying porphyroids. According to historical maps and photos we determined approximate location of the former water pit Vilemina. For the determination of the exact position of the...
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Gravity response of deformation zones around subsurface cavities
Šifnerová, Kristýna ; Blecha, Vratislav (advisor) ; Gürtler, Richard (referee)
The main purpose of this diploma thesis was to determine whether the deformation zone, which arises above intact mining workings in soils, has a measurable gravity effect and influences the interpretation of gravity measurements. The railway tunnel in Březno u Chomutova has been chosen as a test site. We have progressed so that the geotechnical model of the geological environment above the tunnel was calculated first. The model was constructed on the base of two core wells, which were drilled near the tunnel especially for this purpose. The geotechnical model of deformation zone was converted into a density model and its gravity response was calculated. This model was compared with the gravity effect of the tunnel in rock environment without any deformation zone. The difference between effects of these two models gives the gravity response of the deformation zone. We found out that the gravity effect of the deformation zone is insignificant and does not affect the gravity interpretation in the environment of stiff tertiary clays, where the Březno tunnel is excavated. We compared the results of our modeling with the field gravimetric measurements results above the tunnel in Březno. The measurement was realized on three parallel profiles, which reach the tunnel in various depths. The results of...
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