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Influence of velocity model uncertainty in earthquake source inversions
Halló, Miroslav ; Gallovič, František (advisor) ; Duputel, Zacharie (referee) ; Vavryčuk, Václav (referee)
Title: Influence of velocity model uncertainty in earthquake source inversions Author: Miroslav Halló Department: Department of Geophysics Supervisor: doc. RNDr. František Gallovič, Ph.D., Department of Geophysics Abstract: Earthquake ground motions originate from rupture processes on faults in Earth. Constraints on earthquake source models are important for better un- derstanding of earthquake physics and for assessment of seismic hazard. The source models are inferred from observed waveforms by inverse modeling, which is subject to uncertainty. For large tectonic earthquakes the major source of un- certainty is an imprecise knowledge of crustal velocity model. The research topic of this Thesis is the influence of the velocity model uncertainty on the inferred source models. We perform Monte-Carlo simulations of Green's functions (GFs) in randomly perturbed velocity models to reveal the effects of the imprecise veloc- ity model on the synthetic waveforms. Based on the knowledge gained, we derive closed-form formulas for approximate covariance functions to obtain fast and effective characterization of the GFs' uncertainty. We demonstrate that approxi- mate covariances capture correctly the GF variability as obtained by the Monte- Carlo simulations. The proposed approximate covariance functions are...
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Analysis of rupture velocity for selected earthquakes utilizing regional recordings of surface waves
Čejka, František ; Gallovič, František (advisor) ; Zahradník, Jiří (referee)
Supershear earthquake is an interesting phenomena that is still without a robust method for its proving. In 2012 Vallée and Dunham (2012) published a method that studied far-field waveforms from supershear earthquakes. They conclude that unilateral supershear ruptures have similar shape of surface waves on the border of Mach cone as surface waves of smaller earthquake with the similar mechanism and location. In this work we use their method and we developed a script in Python with use of ObsPy library. Our script is capable of downloading and processing data from worldwide seismic databases like IRIS. We tested our program on a supershear earthquake in 2001, Kokoxili, China, which was studied in the original paper. Our results were the same as the original one. Then we use our script to other potential supershear earthquakes: Denali 2002, Yushu 2010 and Aegean sea 2014 to test the method and its results. We conclude that this method is relatively stable for large earthquakes like Kokoxili where we have a big difference between the main shock and the small one. For smaller events there could be a problem with seismic noise and proper setting of frequention.
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Moment tensors of the largest events of the 2016 Central Italy earthquake sequence
Labuta, Martin ; Gallovič, František (advisor) ; Adamová, Petra (referee)
Title: Moment tensors of the largest events of the 2016 Central Italy earthquake sequence Author: Martin Labuta Department: Institute of Hydrogeology, Engineering Geology and Applied Geophysics Supervisor: doc. RNDr. František Gallovič, Ph.D., Department of Geophysics, Faculty of Mathematics and Physics, Charles University Abstract: Central Italy was stuck by an earthquake sequence in 2016, with the largest earthquake of moment magnitude Mw 6.5. 300 people have died after the first earthquake on August 24th, Mw 6.1 and the city Amatrice was heavily damaged. Utilizing the software ISOLA, the low-frequency centroids are found of selected earthquakes with Mw above 4.5. Using these results, the multiple point finite seismic sources are obtained in order to determine fault irregularities. Afterwards, there is a comparison of these results with other academic papers and earthquake catalogs. Keywords: earthquake, ISOLA, moment tensor, centroid
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Three-dimensional ambient noise tomography of the Bohemian Massif
Valentová, Ľubica ; Gallovič, František (advisor) ; Burjánek, Jan (referee) ; Kristek, Jozef (referee)
We have performed 3D ambient noise tomography of the Bohemian Massif. We invert adopted inter-station dispersion curves of both Love and Rayleigh waves in periods 4-20 s, which were extracted from ambient noise cross-correlations, using a two-step approach. In the first step, the inter-station dispersion curves are localized for each period into the so-called dispersion maps. To account for finite-frequency effects, gradient method employing Fréchet kernels is used. Assuming membrane wave approximation of the surface wave propagation at each period, the kernels were calculated using the adjoint method. To reduce the effect of data noise, the kernels were regularized by Gaussian smoothing. The proper level of regularization is assessed on synthetic tests. In the second step, the phase-velocity dispersion maps are inverted into a 3D S-wave velocity model using the Bayesian approach. The posterior probability density function describing the solution is sampled by more than one million models obtained by Monte-Carlo approach (parallel tempering). The calculated variance of the model shows that the well resolved part corresponds to the upper crust (i.e., upper 20 km). The mean velocity model contains mainly large scale structures that show good correlation with the main geologic domains of the Bohemian...
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Dynamic models of earthquake source and modeling of seismicity
Kostka, Filip ; Gallovič, František (advisor) ; Matyska, Ctirad (referee)
In the present thesis we perform modeling of earthquake source using laboratory derive rate-and-state laws of friction. We have developed a code in Fortran 90 for modeling a planar, two-dimensional fault with general dip and heterogeneous distribution of frictional parameters. We use a quasi-dynamic approximation and assume that the fault is submnerged in an infinite elastic half-space. We performed an extensive number of numerical experiments to study the effect of fricitonal parameters distribution on the spatio-temporal complexity of slip on fault. We also study the effect of the so called Coulomb stress changed on clock advance and clock delay of events. For this purpose we use both a homogeneous model and a model of random frictional parameteres which exhibits the Gutenberg-Richter frequency- size dependence in the range of two magnitudes. We find that the effect of Couloumb stress change is nontrivial and depends on factors such as the domain of stress load and the slip velocity on it. Powered by TCPDF (www.tcpdf.org)
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Source Parameters of Microearthquakes and their Uncertainties
Michálek, Jan ; Fischer, Tomáš (advisor) ; Gallovič, František (referee) ; Kwiatek, Grzegorz (referee)
Title: Source Parameters of Microearthquakes and their Uncertainty Author: Jan Michálek Department: Department of Geophysics Supervisor: Doc. RNDr. Tomáš Fischer, PhD., Institute of Hydrogeology, Engineering Geology and Applied Geophysics, Charles University in Prague Abstract: The aim of this thesis is to analyze the spectral methods used for the determination of the earth- quake source parameters like the seismic moment M0 and the corner frequency fc and to apply these meth- ods to seismic data from the West Bohemian region. Considering some assumptions about the source the other important parameters like the source radius r or the stress drop in the source ∆σ can be evaluated. Determination of the parameters is performed in the spectral domain by comparing a simple Brune's source model (non-causal slip on a circular rupture; spectral slope ω−2) with the displacement of the P or S wave. The methods were applied to 56 selected earthquakes of the West Bohemian swarms from 2000 and 2008 by the absolute and relative approach in several modifications. The absolute method allows to determine not only the source parameters but also the quality factor Q (attenuation), which significantly affects the deter- mination of fc. Therefore, the absolute method was applied also as the joint inversion when Q is stabilized....
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Polarization analysis of strong ground motions recorded during the aftershock sequence of the 2009 L'Aquila earthquake
Čejka, František ; Gallovič, František (advisor) ; Zahradník, Jiří (referee)
During broadband modelling of selected events from the aftershock sequence of the l'Aquila earthquake using 1-D model of media, we observe interesting difference between model and real particle polarization on high frequencies. There are two basic types of these polarization disorders. Polarization of particle motion keeps its linear form, but changes its direction or linear polarization changes its linear form to circle polarization. It offers the explanation that these disorders of polarization occur due to the 3D heterogeneities in the crust. In this work, we analyze polarization of published synthetic seismograms modeled with random 3D heterogenitites. It has been shown that the biggest disorders occur in directions in which parcticle movement heads toward the source, and that we can find examples, which qualitatively explain observed polarization disorders.
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Quasidynamic modeling of tectonic faults: segmentation of earthquakes
Kostka, Filip ; Gallovič, František (advisor) ; Souček, Ondřej (referee)
Some tectonic faults are documented to release strain in form of segmented earthquakes, when only a part of the fault fails at a given time, being followed by a rupture of another part of the fault years to tens of years later. In this thesis, our aim is to explain such behaviour using an idealized dynamic-fault model governed by a laboratory derived friction law. To this end, we rst give an overview of a class of rate- and-state friction (RSF) laws, commonly used in modelling of seismic cycles. We perform numerical tests on a spring slider model using the most recent version of the RSF law proposed by Nagata et al. (2012) to better understand its features. Performing extensive numerical experiments with velocity- strenghtening and velocity-weakening zones of varying sizes along an in nite two-dimensional vertical fault, we nd examples of the earthquake segmentation. Powered by TCPDF (www.tcpdf.org)
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Earthquake source models
Adamová, Petra ; Šílený, Jan (advisor) ; Fischer, Tomáš (referee) ; Gallovič, František (referee)
The earthquake source is routinely modeled by moment tensor description. In many cases we need more information about the source process and for that reason we occupy with higher degree moments. This approach allows us to esti- mate non-point characteristics (including some dynamic parameters): geometry of the source, duration of the source process, average slip on the fault, spatial and temporal centroid and rupture velocity vector within the point source ap- proach. This description includes 20 parameters - 6 parameters for standard moment tensor (MT) and 14 parameters for second degree moments (SDM). First, we studied synthetic tests. Large amount of significant earthquakes con- tains false non-DC component which can be caused by approximation finite source by point source. This hypothesis was proved on the case of unilateral rupture. Standard MT contains more than 20 % non-DC components which was reduced to 6 %. In the second part we applied this procedure to real data. We chose large earthquakes (Mw>6) with large non-DC component. We estimated second degree moments for them and compared them with previous studies. Moreover we restitute higher degree moments from data and proved that false non-DC component were caused by source finiteness. In the last part we applied this method to mining data and...
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Anisotropie svrchního pláště pod Severními Apeninami z dat mezinárodního experimentu RETREAT (Itálie)
Munzarová, Helena ; Gallovič, František (advisor) ; Novotný, Oldřich (referee)
Title: Anisotropy of the upper mantle under the Northern Apennines based on data from the international experiment RETREAT (Italy) Author: Helena Munzarová Department: Department of Geophysics Supervisor of the master thesis: RNDr. František Gallovič, Ph.D. Department of Geophysics Consultant of the master thesis: RNDr. Jaroslava Plomerová, DrSc. Institute of Geophysics, Czech Academy of Sciences Abstract: In this master thesis, we process data recorded during the passive seismic experiment RETREAT (2003-2006) in the Northern Apennines with the aim to explore the upper mantle structure in the region. Active orogeny in the Northern Apennines relates to the collision of the Tyrrhenian and Adriatic (subducting westward) plates and is accompanied by an eastward retreat of the trench. Directional dependences of P-wave travel-time deviations together with variations of the fast split polarization azimuths of teleseismic SKS waves are derived from data recorded during experiment RETREAT. Both the fossil anisotropic structure in the mantle lithosphere and the anisotropy due to the present-day flow in the sub-lithospheric mantle are sources of the observed velocity-anisotropy patterns. Thick continental Adriatic plate can be divided into at least two sub-regions with their own fossil fabrics. We have also tried to...
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