National Repository of Grey Literature 4 records found  Search took 0.01 seconds. 
Relative earthquake locations
Jeschkeová, Zuzana ; Bachura, Martin (advisor) ; Doubravová, Jana (referee)
This bachelor thesis concerns the issues related to techniques of earthquake locations. The methods can be divided into a two groups: absolute (Geiger method, grid search) and relative (master-event, hypoDD) ones. A greater emphasis is put on the latter ones - the relative methods. In these methods make use of so-called differential times - absolute time differences between phase arrivals of two earthquakes. The differential times can be estimated by the means of waveform cross-correlations. Our main objective was to compare cross-correlated differential times with the real ones and determine their accuracy. The analysis revealed that the difference - bias in differential time is present and for tho earthquakes with different magnitude it can reach 0.06 s. Keywords: locations, earthquakes, cross-correlation, seismograms
Analysis of coda waves of the West-Bohemian earthquakes
Bachura, Martin ; Fischer, Tomáš (advisor) ; Vavryčuk, Václav (referee)
Coda of high frequency earthquakes contains information about attenuation propetries of the environment between earthquake hypocentre and seismic station. By application of different methods of coda anlysis one can derive these properties. I applied three methods to seismograms from autumn 2011 from WEBNET network monitoring seismic activity in West Bohemia/Vogtland area: basic method to derive Qc parameter of the environment, and two methods that allow for separation of intrinsic attenuation (Qi) and attenuation due the scattering (Qsc): method MLTWA (Multiple Lapse Time Window Analysis) and method based on energy flux model. Values of Qc are relatively small (from 22 to 600, which depends on the length of the window in which the analysis is carried out and on the frequency and station used), which is in good agrement with the high seismic activity in the area. Qc shows frequency, depth and lateral dependances. It increases with frequency and depth and in the southwest direction. The applicability of methods for separation of Qi and Qsc are limited. With short hypocentral distancies as we have coda is not affected by scattering. Because of this, I was unable to use MLTWA method and the method of energy flux model was usable to derive only the values of Qi. These values are from 120 (1,5 Hz at...
Seismic noise analysis at selected stations of the WEBNET network
Bachura, Martin ; Fischer, Tomáš (advisor) ; Růžek, Bohuslav (referee)
Seismic signal is affected by noise of non-geological origin. The main source of seismic noise is in human activities. Seismic noise of human origin occurs in the frequency range from one to the first tens of Hz. The noise intensity limits the lower level of the earthquake size that can be recorded by a seismic network. The aim of this thesis is to analyze the seismic noise on selected stations of the West Bohemian seismic network WEBNET which operates in the area since the early nineties. The earthquakes in West Bohemia/Vogtland are manifested in the form of long-lasting earthquake swarms with the magnitudes ranging up to ML = 3.8. The way how the seismic noise influences the seismic stations and their capability of recording small earthquakes can be classified by a statistical and time-frequency analysis. We applied this method to the selected stations NKC, KRC and SKC. The results show that the effect of noise does not deteriorate the seinsitivity of the three stations for recording small earthquakes. Despite of quite good results, some differences occur among the three stations, which are most probably caused by the distance of the stations to the populated areas. The smallest noise influence is observed at the stations located far from settlement (NKC and KRC) compared to the station located in a small...

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