DBPapers
DOI: 10.5593/SGEM2014/B11/S5.068

MAPPING THE RESONANCE FREQUENCY OF SEDIMENTARY LAYERS IN THE VICINITY OF A PERMANENT SEISMIC STATION IN UNDERMINED AREA

M. Lednicka, Z.Kalab
Wednesday 1 October 2014 by Libadmin2014

References: 14th International Multidisciplinary Scientific GeoConference SGEM 2014, www.sgem.org, SGEM2014 Conference Proceedings, ISBN 978-619-7105-07-0 / ISSN 1314-2704, June 19-25, 2014, Book 1, Vol. 1, 513-520 pp

ABSTRACT
This paper presents an analysis of site effect in Stonava locality, the Karviná region (Czech Republic). This region is a populated area, where underground mining activities are still active, and the vibration effect on the surface has been documented by observations for a long time. The vibration effect on the surface, mainly mining induced seismic events, is evaluated using solitaire seismic stations situated in selected surface objects. Local geology in the area of Stonava is very complicated. A thin layer of Quaternary sediments covers the Tertiary sediments of a different thickness (400 – 600 m) and a different stiffness. Several significant faults have also been found there. The local geology has a significant influence on the intensity of vibrations on the surface. The first studies by means of spectral ratio methods were carried out in the Karviná region mostly from the records of mining induced seismic events generated in the Karviná Coalfield. It was found out that the spectral ratio exhibits significant peaks in localities covered by sedimentary layers. These ratio curves for individual measured points document the significance of amplification of seismic effect on the surface in this area. Two or more peaks were often detected which indicates a complexity of subsurface layers. From the geological point of view, it is also necessary to consider changes of hydro-geological regime of the area and a deformation of the terrain. This effect might be evaluated e.g. by using special maps of potential conflicts of interest between the use of residential area and mining effects. The maps have been developed to estimate possible seismic effect in undermined areas with different classes of foundation conditions. It has also been found out that an area of about 2 x 2 km needs at least two seismic stations: One in favourable foundation conditions and the other one in critical foundation conditions as the seismic effect may vary due to changes of geological conditions. This paper summarizes the evaluation of resonance frequency of sedimentary layers in a selected locality. Short-term measurements of seismic noise were performed at about 15 places near the permanent seismic station in Stonava village. Resonance frequency was determined using the HVNR method (horizontal to vertical noise ratio). Obtained results were compared with the previous ones specified for the permanent seismic station.

Keywords:HVNR method, mining induced seismicity, undermined area, site effect, seismic noise