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Magnitude-frequency distribution of the seismic activity preceding the Fagradalsfjall 2021 eruption
Severini, Bianca Georgina ; Fischer, Tomáš (advisor) ; Hrubcová, Pavla (referee)
iv Abstract This bachelor's thesis focuses on the estimation of the parameter b derived from the Gutenberg- Richter law talking about the dependency of the events' frequencies on their magnitude during seismic activity preceding the effusive eruption on 19th March 2021 Fagradalsfjall, Iceland. The data were selected in space and time from seismic catalogue comprising records from 10th January 2021 until 10th August 2022. The maximum likelihood method was used when computing the b value and the goodness of fit method for estimating the magnitude of completeness MC. In order to give a comparison to resulting b values, newly introduced method called b-positive was added to this thesis. B-positive was designed to withstand temporal incompleteness of the seismic catalogue and to be fully independent on the MC. All values were computed with computational script made in MATLAB in cooperation with consultant of this thesis. It was searched for the space and time dependency among the selected seismic data clusters in Fagradalsfjall and Krýsuvík system. Results at the Fagradalsfjall system are proving the activity was connected to tectonic movements and to the intrusion of magmatic dyke. Divergent plate boundary in this area shows lower values in comparison with the magmatic dyke which has higher values. For the...
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Crustal Structure of the Bohemian Massif Based on Seismic Refraction Data
Hrubcová, Pavla ; Vavryčuk, Václav (advisor) ; Plomerová, Jaroslava (referee) ; Švancara, Jan (referee)
The deep structure of the Bohemian Massif, the largest stable outcrop of the Variscan rocks in central Europe, was studied using the data of the international seismic refraction and wide- angle reflection experiments CELEBRATION 2000, ALP 2002 and SUDETES 2003. The data were interpreted by seismic tomographic inversion and by 2-D trial-and-error forward modelling of the P and S waves. Above, additional constraints on the crustal structure were imposed by reflectivity or gravity modelling, and by receiver function interpretation. Knowledge of the crustal velocity structure in the Bohemian Massif was complemented by its azimuthal variation. Though consolidated, the Bohemian Massif can be subdivided into several tectonic units separated by faults, shear zones, or thrusts reflecting varying influence of the crust forming processes. The resultant velocity models determined different types of the crust-mantle transition reflecting variable crustal thickness and delimiting contacts of these tectonic units at depth.
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Subduction factory interaction of subduction-related magma with the overlying lithosperic wedge
Kuna, Václav ; Špičák, Aleš (advisor) ; Hrubcová, Pavla (referee)
III Abstract The world's largest earthquakes, the most destructive tsunamis and the most explosive vol- canism are generated at subduction zones at convergent plate margins. Despite of high societal and economic importance of these areas, there are still some poorly understood processes, such as the process of magma generation and ascent to the Earth surface. This thesis contributes to the solution of the problem of location of source areas of calc-alkaline magma and its migration. It consists of two parts: in the first one, the phenomenon of vol- canism at convergent plate margins and seismological background are described, while the second part explores structures in the lithosphere beneath volcanoes in the broader region of the Banda Arc (Indonesia). For the purposes of the research, the ISC hypocentral de- terminations based on data from the global seismic network, relocated by a procedure of Engdahl et al. and collected in the so called EHB database were used. The analyses of spa- tial, time and magnitude dependencies in the dataset of earthquakes occurring within the Banda Arc area enabled us to formulate several conclusions: The occurrences of strong teleseismically recorded earthquakes in the lithospheric wedge beneath volcanoes suggests that the respective rock medium is not partially melted....
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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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The crust/mantle boundary in geodynamically active area of West Bohemia
Podolník, Jan ; Hrubcová, Pavla (advisor) ; Málek, Jiří (referee)
The region of West Bohemia is one of the most geodynamically active areas of Central Europe. The activity is characterized by many natural phenomena such as recurrent seismic swarms. The crustal structure of the region was subject of many geophysical investigations that revealed increased reflectivity of the lower crust. In this thesis, we adapt the multi-azimuthal approach for the detection of crustal discontinuities developed by Hrubcov'a et al. (2013). We apply the ap- proach on waveforms of the 2000 and 2008 swarms that occurred in the Nov'y Kos- tel focal area registered by several German stations. Analysis of the data of more distant German stations allowed expanding of the information about the depth and character of the crust/mantle transition in a broader area of the West Bo- hemia region. The results show a thickening of the zone in Germany with in- creasing distance from the epicentral area. Such findings are in agreement with previous active and passive seismic experiments.
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Relation of earthquakes and volcanism in West Bohemia and Iceland
Labuta, Martin ; Horálek, Josef (advisor) ; Hrubcová, Pavla (referee)
English abstract Most earthquakes occur as accompanying activity of large tectonic earth- quakes at the edges of lithospheric plates. Another type of seismic activity are earthquake swarms, which are characterized by series of earthquakes with several dominant shocks of similar strength. The origin of earthquake swarms is mostly combination of tectonic stress and movement of hydrothermal flu- ids along the fault plane. Mainly, swarms are observed within volcanic areas but even in areas without recent volcanic activity, like in West Bohemia. This region lies above an intra-continental rift zone the Eger Rift and it has been seismologically active in past years, including swarms in 2008, 2011, 2013 and 2014 monitored by the local seismic network WEBNET with dominant shocks of magnitudes below ML 4.5. All these events are located in depths between 7 and 11 km and they create 8 km long focal zone with N-S orientation. However, the latter swarm changed its character from a continuous occurrence with a dominant shock to a main shock and aftershock activity. Contrary, the region of Reykjanes peninsula in Iceland is located above the Mid-Atlantic Ridge, which results in shallower depths between 2 to 9 km. Additionally, the seismic energy in this area is released as a typical swarm-like activity and migrates along...
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Seismograph installation and complex analysis of recorded data
Vaško, Oskar ; Fischer, Tomáš (advisor) ; Hrubcová, Pavla (referee)
This thesis deals with assembly of a school seismograph and a common analysis of recorded data. A garden-gate type seismometer was assembled within the first part of my thesis. The pendulum construction of the seismometer enables recording of a horizontal component of seismic signal. The data analysis involves mainly processing of seismic noise in the buiding of Geologic Section of Faculty of Science in Prague - Albertov. Several eigenfrequencies of the building, which indicate the liability of the construction to be affected by ground motions, were found. As a supplement few recorded earthquakes were identified. The seismic noise analysis led to a finding of a relation between eigenfrequency variation and outdoor temperature in the form of a positive correlation between daily temperature average and eigenfrequency.
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Subduction factory interaction of subduction-related magma with the overlying lithosperic wedge
Kuna, Václav ; Špičák, Aleš (advisor) ; Hrubcová, Pavla (referee)
III Abstract The world's largest earthquakes, the most destructive tsunamis and the most explosive vol- canism are generated at subduction zones at convergent plate margins. Despite of high societal and economic importance of these areas, there are still some poorly understood processes, such as the process of magma generation and ascent to the Earth surface. This thesis contributes to the solution of the problem of location of source areas of calc-alkaline magma and its migration. It consists of two parts: in the first one, the phenomenon of vol- canism at convergent plate margins and seismological background are described, while the second part explores structures in the lithosphere beneath volcanoes in the broader region of the Banda Arc (Indonesia). For the purposes of the research, the ISC hypocentral de- terminations based on data from the global seismic network, relocated by a procedure of Engdahl et al. and collected in the so called EHB database were used. The analyses of spa- tial, time and magnitude dependencies in the dataset of earthquakes occurring within the Banda Arc area enabled us to formulate several conclusions: The occurrences of strong teleseismically recorded earthquakes in the lithospheric wedge beneath volcanoes suggests that the respective rock medium is not partially melted....
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Crustal Structure of the Bohemian Massif Based on Seismic Refraction Data
Hrubcová, Pavla ; Vavryčuk, Václav (advisor) ; Plomerová, Jaroslava (referee) ; Švancara, Jan (referee)
The deep structure of the Bohemian Massif, the largest stable outcrop of the Variscan rocks in central Europe, was studied using the data of the international seismic refraction and wide- angle reflection experiments CELEBRATION 2000, ALP 2002 and SUDETES 2003. The data were interpreted by seismic tomographic inversion and by 2-D trial-and-error forward modelling of the P and S waves. Above, additional constraints on the crustal structure were imposed by reflectivity or gravity modelling, and by receiver function interpretation. Knowledge of the crustal velocity structure in the Bohemian Massif was complemented by its azimuthal variation. Though consolidated, the Bohemian Massif can be subdivided into several tectonic units separated by faults, shear zones, or thrusts reflecting varying influence of the crust forming processes. The resultant velocity models determined different types of the crust-mantle transition reflecting variable crustal thickness and delimiting contacts of these tectonic units at depth.
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