Acta Montanistica Slovaca (Oct 2007)
Site response investigation at the seismological station Ostrava-Krásné Pole (OKC)
Abstract
Seismic waves generated by earthquakes, quarry blasts, ocean waves and various technological sources cause vibrations that spread through underlying strata into the broad vicinity of these sources. The aim of our experiments was to identify and characterize possible sources of seismic noise generated primarily by technical sources in the Ostrava-Karviná urban agglomeration, which is part of north-eastern Moravia (Czech Republic). The solution of this issue was initiated upon the demand for new knowledge of particle velocity amplitudes and spectral content of disturbing effects, using a newly developed data acquisition method and a system of digitized data processing. A detailed investigation of the influence of different seismogeological conditions at the two sites of observation was performed. While the seismic cellar (OKC A: φ = 49.8375o N, λ = 18.1472o E and h = +272 m) is underlain by glaciofluvial sediments (clay loams, sands and gravels), the thickness of which is approximately up to 22 m, the underlying beds in the nearby experimental gallery (OKC B: φ = 49.8353o N, λ = 18.1423o E, and h = +250 m) are represented by compact Culm-facies schists (Lower Carboniferous). The thickness of these Culm-facies that represent the underlying bed of the coal-bearing Upper Carboniferous (Namurian A) is about 1,200 m. The experimental gallery is situated at a distance of approximately 450 m from the original seismic cellar and about 22 m below its bottom. Different physical-mechanical properties of sub-surface layers at both sites result in different values of acoustic impedance, which naturally influences the particle velocity values, while the shape of calculated amplitude spectra displays a noticeable similarity. On the basis of experimental measurements, some results related to particle velocities and corresponding amplitude spectra of seismic noise are briefly discussed.
