STUDY OF SITE EFFECT IN THE MOST BASIN AREA, CZECH REPUBLIC

References: 15th International Multidisciplinary Scientific GeoConference SGEM 2015, www.sgem.org, SGEM2015 Conference Proceedings, ISBN 978-619-7105-33-9 / ISSN 1314-2704, June 18-24, 2015, Book1 Vol. 3, 1027-1034 pp

ABSTRACT
The Most Basin (North Bohemia, Czech Republic) is a part of a Tertiary sedimentary basin, filled with sedimentary material mostly during the Miocene era. In that period, a layer of up to 500 m of clays, sands and organic matter was accumulated. This became the basis of coal seams of a thickness of 25 - 45 m. This region belongs to the richest European deposits of lignite (brown coal), which has been extracted here since the second half of the 19th century, mostly by extensive surface mining.
Blasting operations are used as a part of mining technology in open-pit mines and this mining activity represents the main source of seismic loading of inhabited areas in the surroundings of the mine. The vibration effect caused by blasting operations takes an unusual shape at the Most Basin area. The duration of the recorded wave patterns is up to 35 s. Wave patterns recorded at a distance of 2 to 5 km far from the blast show body waves in groups, the duration of which is from 3 to 7 s. The group of body waves is followed by an intensive group of surface waves with a pattern of harmonic vibration lasting for 15 - 20 s. The prevailing frequency in this part of the wave pattern is up to 2 Hz and the maximum recorded value of vibration velocity also occurs in majority of these wave groups. We suppose that this unusual wave pattern is connected with the site effect caused by surface geology. To confirm this hypothesis, the recorded wave patterns of blasting operations were analysed in time and frequency domain in detail. Seismic noise measurements were performed in the surroundings of the open-pit mine at the edge of the basin and gained resonant frequencies were compared to prevailing frequencies resulting from the analysed records of blasting operations at the investigated locality.

Keywords: blasting operation, site effect, HVNR method, Most Basin