Comparison of near-surface layers spectral characteristics under the seismic stations «Trosnyk», «Uzhgorod», «Mezhgirya» calculated using finite element method and obtained experimentally
The purpose of this work was to calculate the theoretical transfer characteristics of the sedimentary layers under the seismic stations «Trosnyk», «Uzhgorod», «Mizhgirya» of the Carpathian seismic network using the Finite element method (FEM). These results are used for comparison with the dynamic parameters of near-surface layers received experimentally; for checking the conformity of investigated environment resonance properties obtained by these methods for the possibility of their application in regional seismological studies. The research was carried out by solving the direct dynamic seismic problem using the finite element method. This method of mathematical modeling allows making calculations for models that are complex in their structure. When solving the direct dynamic seismic problem using FEM, the opportunity to take into account various exchange effects inside the model does not forfeit. Also, we can calculate models with the complex geometric environment structure and various inclusions. Using the developed technique of wave field simulation by finite element method, oscillations for models of the seismic section under the «Trosnyk», «Uzhgorod» and «Mizhgirya» stations were investigated. According to the simulation results, theoretical spectral ratios for these stations were calculated. For the Seismic Station «Mizhgirya», we observe the coincidence of two interference maxima at a frequency of 4 and 10 Hz for both charts: experimental and theoretical. For the Seismic Station «Uzhgorod», the graphs obtained by the experimental and modeling method showed identical behavior throughout the frequency range. These charts provide a stable source of noise within the city. For the Seismic Station «Trosnyk» there is a discrepancy in the behavior of experimental and model charts above 6 Hz. Such results are due to the high level of groundwater under the seismic station, which was not taken into account in the creation of the model for calculating using the finite element method.
The spectral characteristics of near-surface layers under the «Trosnyk», «Uzhgorod» and «Mizhgіrya» seismic stations were calculated by the finite element method for the first time. The results of mathematical modeling were compared with experimental measurements. The knowledge about the dynamic parameters of the upper sediment layers under seismic stations, which are the largest filter of oscillation frequencies in the spectral range, will allow more accurate interpretation of registered by these stations occurrences. The calculated spectral ratios give a possibility to estimate the degree of environmental influence on stations’ seismic signals recording, which will be the largest at frequencies corresponding to the received resonance maxima and minima. These results should be taken into account when evaluating the parameters of possible seismic effects in the territory.
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