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Use of borehole seismometers for the study of seismic wave attenuation
Konrádová, Diana ; Fischer, Tomáš (advisor) ; Hrubcová, Pavla (referee)
Nowadays, the seismic activity is most often recorded by seismic stations on the surface of the Earth. Nevertheless, in the recent years, Czech Republic started installing the borehole seismometeres. In Hartoušov in West Bohemia and Litoměřice, new monitoring seismic boreholes were built and borehole seismometers were installed. On data gathered by the seismometers in these areas, I have applied the spectral ratio method, in order to fully understand and further specify the influence of the near-surface layer. The data stemmed from various levels of depths and distinctive geological environments. Through the analysis of amplitudes, I defined their intensification on the surface and through the definition of the signal and noise ratio I showed what the significance of the use of borehole seismometers is in terms of improving the sensitivity of monitoring. The following spectral analysis served not only as a comparison with the theoretical outcomes, but also to determine the quality factor Q in the near-surface layer in Litoměřice and Hartoušov. Lastly, I evaluated the value of Q on the scale of 5 to 30 Hz, the influence of the local effects and geology.
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Earthquake swarms in West Bohemia - their onset and fade
Khodjaev, Alisher ; Fischer, Tomáš (advisor) ; Boušková, Alena (referee)
During the last 30 years, the activity of various earthquake swarms has been instrumentally recorded in the West Bohemian earthquake region. This work is studying the spatiotemporal evolution of seismicity preceding and following selected swarms from 1992 to 2020. The introductory part contains a brief description of the area of interest. The research part acquaints the reader with the necessary basics of seismology. In the next, phenomenon of earthquake swarms is described - their typical activity, possible mechanisms of origin, examples from the world and from the West Bohemia. In the practical part, using seismic catalogs, seismic activity preceding and following selected swarms is visualized. The aim is to find some regularities in the spatiotemporal evolution of the West Bohemian earthquake swarms. Using the visualization of the activity of selected swarms and the author's own interpretation, no regularities were found. For a more relevant conclusion a quantitative analysis should be carried out.
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Automatic processing of microseismic data and their relation to the hydraulic injection
Vlček, Josef ; Fischer, Tomáš (advisor) ; Plicka, Vladimír (referee) ; Růžek, Bohuslav (referee)
Microseismic monitoring is an integral part of scientific experiments or industrial operations associated with the hydraulic fracturing of bedrock, which is an effort to increase the permeability of rocks in the area and improve the exploitation, whether of heat, oil or natural gas. Monitoring of such newly formed or growing original fractures, usually followed by seismic events, is very important for observation and describing the hydraulic fracturing itself and its progress over time. Since the number of such events recorded is usually very high, classical methods of earthquake processing, where the arrival times of seismic waves are determined manually, seem to be very inappropriate. For this reason, automatic methods are used to process such datasets, which do not require manual determination of the arrival times of the seismic waves. In our case, the data were recorded by a dense network of surface receivers arranged in the shape of a ten-arm star. It was a total of more than nine hundred groups of vertical geophones, of which more than a quarter were also supplemented by a three-component seismic sensor. We then created an automatic procedure for the described network, the result of which is the determination of the location and the source mechanism for each seismic event. The recorded...
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Inversion and Depth Range of Dipole Electromagnetic Induction Measurements in Geophysics
Moura de Andrade, Fernando César ; Fischer, Tomáš (advisor) ; Godio, Alberto (referee) ; Velímský, Jakub (referee)
Inversion and Depth Range of Dipole Electromagnetic Induction Measurements in Geophysics Fernando César Moura de Andrade Institute of Hydrogeology, Engineering Geology and Applied Geophysics Faculty of Science, Charles University Electromagnetic induction geophysical methods are, basically, composed by a transmitter which produces a magnetic field and a set of receivers which measure the primary magnetic field, from the transmitter, superimposed by secondary magnetic fields inducted in the subsurface. Equipment operating at, relatively, low frequencies and with short distances between the transmitter and the receivers are usually called conductivity meters and operate at low inductions numbers. The depth of investigation, in such kind of equipment, depends mainly on the transmitter-receiver distance, on the orientations of the magnetic dipoles and the height of the instrument from the ground, in order that a depth sounding can be done changing these parameters in a single measurement location. Making a series of these multi-configuration measurements, two-dimensional, or even three-dimensional surveys, can be performed and, subsequently, inverted in order to produce an image of the subsurface of the earth. Forward modelling and inversion of multi-configuration electromagnetic induction data can be made...
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Relocation of the 1962 earthquake swarm in West Bohemia
Konrádová, Diana ; Fischer, Tomáš (advisor) ; Doubravová, Jana (referee)
Since the swarm at the turn of 1985/86 the current activity of seismic swarms in western Bohemia takes place mainly in the area of Nový Kostel at the eastern edge of the Cheb basin. However, the location of previous activities, where only more remote seismic stations were in operation, is not exactly known. This also applies to the swarm of 1962, which this bachelor thesis is focused on. Seismic bulletin data are available from eight seismic stations at a suitable distance for sufficient localization quality for this swarm. The theoretical part of the thesis presents research results of fundamental existing localization methods and their properties. In the practical part, the location of the earthquake epicenter of swarm 1962 is presented.
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Automated determination of earthquake source parameters
Vackář, Jiří ; Zahradník, Jiří (advisor) ; Evangelidis, Christos (referee) ; Fischer, Tomáš (referee)
Title: Automated determination of earthquake source parameters Author: Jiří Vackář Department: Department of Geophysics Supervisor: prof. RNDr. Jiří Zahradník, DrSc., Department of Geophysics Abstract: The thesis deals with methods for automated inversion of seismic source parameters. We studied the influence of structure model used and show an ex- ample how the existing model can be improved. We have developed a new, fully automated tool for the centroid moment tensor (CMT) inversion in a Bayesian framework. It includes automated data retrieval from ArcLink server or local data storage. Step-like disturbances are detected using modeling of the distur- bance according to instrument parameters and such components are automati- cally excluded from further processing. Frequency ranges for the filtration and time windows for the inversion are determined automatically due to epicentral distance. Full-waveform inversion is performed in a space-time grid around a provided hypocenter. A data covariance matrix calculated from pre-event noise yields an automated weighting of the station recordings according to their noise levels and also serves as an automated frequency filter suppressing noisy frequency ranges. The method is tested on synthetic and observed data. It is applied on a dataset from the Swiss seismic...
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Earthquake influence on groundwater levels in West Bohemia/Vogtland
Krajinová, Markéta ; Fischer, Tomáš (advisor) ; Horálek, Josef (referee)
This Batchelors thesis focuses onto possible earthquake influence on groundwater levels in West Bohemia/Vogtland area. The thesis describes geology, hydrogeology and seismic activity of the area. Further describes possible earthquake influence on ground water level and mentions world and local sightings. The area is known for its earthquake swarms up to ML=4, therefore the thesis also deals with an influence of three local earthquakes. They occurred in 2014 with hypocentre near Nový Kostel in West Bohemia and their magnitudes were ML =3,5; 4,4 and 3,6. The thesis further analyses ground water level records of 38 wells at localities: Františkovy Lázně, Lázně Kynžvart, Karlovy Vary, Německo and sokolovská pánev. A polarity of ground water level change after the earthquakes is compared to volumetric strain caused by the earthquakes. Overall agreement is found at few sites, which indicates possible effect of earthquake generated static stress change to the ground water level.
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