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Joint inverse modeling of coseismic and postseismic slip of the 2014 South Napa, California, earthquake
Premus, Jan ; Gallovič, František (advisor) ; Burjánek, Jan (referee) ; Tinti, Elisa (referee)
Title: Joint inverse modeling of coseismic and postseismic slip of the 2014 South Napa, California, earthquake Author: Jan Premus Department: Department of Geophysics Supervisor: prof. František Gallovič, Department of Geophysics Abstract: Slip at tectonic faults spans a wide range of time scales, from tens of seconds of earthquake coseismic rupture to months of aseismic afterslip, recorded in seismograms and geodetic data. The two slip phenomena are often studied separately, focusing on kinematic aspects. We introduce a Bayesian method for physics-based joint inverse modeling of an earthquake slip and afterslip, employ- ing a unifying rate-and-state friction law. To simulate the rupture propagation, we develop an efficient finite-difference open-source code FD3D TSN. GPU ac- celeration of the code yields speed-up by a factor of 10 with respect to a CPU, enabling hundreds of thousands of earthquake simulations in a reasonable time. We also implement a quasi-dynamic afterslip simulation using a boundary inte- gral element method. We apply the Bayesian dynamic inversion to the 2014 Mw 6.0 Napa earthquake. We reveal the dynamics of coseismic and postseismic slip in terms of stress and friction in a unified model, reconciling previous disjunctive analyses of the event. We show that the two types of slip are mostly...
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Analysis of volcanic tremor during the 2021 Fagradalsfjall eruption
Sova, František ; Fischer, Tomáš (advisor) ; Burjánek, Jan (referee)
Volcanic tremors are low frequency seismic events, occurring prior to or during eruptions and are believed to be caused by the movement of magma. The study of those events can reveal subsurface processes during volcanic activity, furthermore it can help to reconstruct eruptions, which cannot be observed directly. The presented study describes the volcanic tremor during the 2021 Fagradals- fjall eruption in Iceland. Seismic data from several stations were processed to produce a half-year record of volcanic activity. Additionally, the tremor ampli- tude attenuation was investigated. The seismic record was marked by a reoccurring tremor signal in the fre- quency band 1-10 Hz, which temporally matched with the different phases of effusive eruption. Its amplitudes varied in time, showing three distinct pat- terns. The weak continuous tremor in the first weeks of eruption transitioned into regular pulses, lasting several minutes, and later into a different pulsation with a 1.5-day period. Those variations might reflect the changes in geometry and magma flow of the underground magmatic system. 1
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Seismic Site Effects (Data Analysis and Modelling)
Caserta, Arrigo ; Zahradník, Jiří (advisor) ; Růžek, Bohuslav (referee) ; Burjánek, Jan (referee)
A comprehensive study of the soil shaking under the seismic wave-field ex- citation is presented. It includes theoretical, geological, geotechnical, data analysis and numerical simulations aspects. The aim is to quantify the main parameters allowing the estimate of the soil shaking in urban areas for better mitigating seismic risk due to future earthquakes. The city of Rome has been chosen as a case study because of its high density of popula- tion and large concentration of historical monuments with high earthquake vulnerability. This study improves significantly the knowledge concerning the detailed near-surface geology of the chosen study area of Rome, ful- fills the absence both of knowledge concerning its geotechnical properties and earthquake data recordings in the city. Among others, it allows for a better explanation of the spatial damage pattern observed in the city due to earthquakes in the past. The main innovations include the construction and long-term operation a seismic array in the city, analysis of the natural seismic noise, and instrumental recordings of the 2009 L'Aquila earthquake sequence. The 3D array (including a borehole sensor at 70-m depth) is the first one in Italy planned, realized and operated within an urban area, and the first one that recorded a significant earthquake in...
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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 the earthquake source
Kostka, Filip ; Gallovič, František (advisor) ; Burjánek, Jan (referee) ; Kaneko, Yoshihiro (referee)
Dynamic models of the earthquake source allow simulating the evolution of stress and slip at tectonic faults by coupling the equations of motion in a volume surrounding the fault with a constitutive law that represents the surface forces acting on the fault. In the first part of the thesis, we review important properties of shear rupture for brittle, linear slip-weakening, and rate-and-state constitutive laws. In the second part of the thesis, we present two studies utilizing 3-D dynamic modeling at both long (hundreds of years) and short (seconds) time scales. In the first study, we model seismic cycles using the rate- and-state laws of friction and perform a parametric exploration of the effects of sudden intra-cycle shear stress perturbations on the clock advance or delay of the subsequent large event. We find that when the perturbation is applied during specific time intervals, the earthquakes following the perturbation are only small ruptures that do not completely release stress on the whole fault. The time interval between large earthquakes may thus be prolonged up to 80% when compared to the unperturbed cycles. We reproduce this behavior on a numerical heterogeneous model of the Parkfield segment of the San Andreas fault and demonstrate that the mechanism could have been responsible for the observed large...
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Ambient noise investigation of rock structures in Bohemian Paradise
Müller, Jozef ; Burjánek, Jan (advisor) ; Zábranová, Eliška (referee)
We carry out non-invasive ambient noise investigation of rock structures in Bohemian Paradise (Bohemian Cretaceous Basin, Czech Republic). The study is focused on two key topics: 1) An in-situ elastic moduli estimate of competent, horizontally deposited sandstone layers. This is done by performing an ambient noise array measurement. The recording is processed with f-k array analysis, from which frequency-dependent Love and Rayleigh wave dispersion curves as well as the Rayleigh wave ellipticity are retrieved. The data are inverted for P- and S-wave velocity profiles, from which the Young's and shear modulus are successfully estimated. 2) Study of local response of Kapelník rock tower. We analyse a dataset of ambient noise recordings from the top of the tower and from its foot. Information about tower oscillation frequencies and directions, together with amplification ratios, are retrieved from particle motion polarisation analysis and from site-to-reference spectral ratios. The Euler-Bernoulli beam theory is finally used to interpret the measured data using the elastic moduli estimated from the noise array measurement. Keywords: Bohemian Paradise, rock tower, seismic ambient noise, seismic surface waves
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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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Recent movements on the Cordillera Blanca fault (Peru)
Sánchez Valdiviezo, Lisseth del Pilar ; Fischer, Tomáš (advisor) ; Burjánek, Jan (referee)
The studied area is located the Cordillera Blanca range (central Peru). This mountain range is, at its western foot, bordered by a 210 km long fault system bearing the same name. It is on this fault system where 3D monitoring of recent movements with the use of dilatometer TM-71 takes place. Displacements along this fault are analyzed with regard to the static stress changes caused by earthquakes. Moreover, processing and interpretation of data from ERT measurement performed across the investigated fault at Pitec locality (10 km from Huaraz) are presented. The resulting geoelectrical models of the measurement carried out in July 2016 at the mentioned locality indicate that this area is formed by rocks with very high resistivity values. It is a consequence of the presence of the moraine material (7 to 12 m thick) and of the base of the colluvial deposits composed of granites and granodiorites. At this site the fault has a dip angle of 70ř. The 3D displacement monitoring results of the studied fault at the Pitec locality indicate that the selected site is generally very stable. The dilatometer TM-71 has been in operation since 1997 and has been measuring movements on the Cordillera Blanca fault in all the three dimensions (perpendicular to the fault - opening, along the fault in horizontal plane,...
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Seismic Site Effects (Data Analysis and Modelling)
Caserta, Arrigo ; Zahradník, Jiří (advisor) ; Růžek, Bohuslav (referee) ; Burjánek, Jan (referee)
A comprehensive study of the soil shaking under the seismic wave-field ex- citation is presented. It includes theoretical, geological, geotechnical, data analysis and numerical simulations aspects. The aim is to quantify the main parameters allowing the estimate of the soil shaking in urban areas for better mitigating seismic risk due to future earthquakes. The city of Rome has been chosen as a case study because of its high density of popula- tion and large concentration of historical monuments with high earthquake vulnerability. This study improves significantly the knowledge concerning the detailed near-surface geology of the chosen study area of Rome, ful- fills the absence both of knowledge concerning its geotechnical properties and earthquake data recordings in the city. Among others, it allows for a better explanation of the spatial damage pattern observed in the city due to earthquakes in the past. The main innovations include the construction and long-term operation a seismic array in the city, analysis of the natural seismic noise, and instrumental recordings of the 2009 L'Aquila earthquake sequence. The 3D array (including a borehole sensor at 70-m depth) is the first one in Italy planned, realized and operated within an urban area, and the first one that recorded a significant earthquake in...
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