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| Titel |
Site effects and soil-structure resonance study in the Kobarid basin (NW Slovenia) using microtremors |
| VerfasserIn |
A. Gosar |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1561-8633
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| Digitales Dokument |
URL |
| Erschienen |
In: Natural Hazards and Earth System Science ; 10, no. 4 ; Nr. 10, no. 4 (2010-04-14), S.761-772 |
| Datensatznummer |
250008081
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| Publikation (Nr.) |
 copernicus.org/nhess-10-761-2010.pdf |
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| Zusammenfassung |
| The town of Kobarid is located in one of three areas with the highest
seismic hazard in Slovenia. It was hit by several 1976–1977 Friuli sequence
earthquakes and recently by the 1998 and 2004 Krn Mountains earthquakes
which caused damage of intensity up to VII EMS-98 scale. The town is located
in a small basin filled with heterogeneous glaciofluvial Quaternary
sediments in which site effects due to soft sediments are expected. The
existing microzonation which is based on surface geological data only is
inadequate, and no borehole or geophysical data are available in the basin
that would allow a modelling approach of site effects assessment. The
microtremor horizontal-to-vertical spectral ratio (HVSR) method was
therefore applied in order to assess the fundamental frequency of the
sediments. Investigations were performed on a 100×100 m dense grid and 106
free-field measurements acquired. Clear HVSR peaks were obtained in the
majority of the surveyed area. The eastern part of the basin is
characterized by two well separated peaks which indicate distinct shallow
and deep impedance contrasts. The iso-frequency map of sediments shows a
distribution in a broad range of 1.8–22.2 Hz. The observed frequencies can
be related to the total thickness of Quaternary sediments (sand, gravel) in
the western part of the basin only. They are deposited over bedrock built of
Cretaceous flysch. In the eastern part the obtained fundamental frequencies
are influenced by the presence of a shallow conglomerate layer inside sandy
gravel or lacustrine chalk. The extent of these layers was not known before.
Microtremor measurements were also performed inside 19 characteristic
buildings of various heights (from two to four stories), and longitudinal
and transverse fundamental frequencies determined from amplitude spectra. A
potential of soil-structure resonance was assessed by comparing building
frequencies with the free-field sediments frequencies derived from the
iso-frequency map. For two surveyed buildings a high danger of
soil-structure resonance was assessed and for three buildings the danger was
of medium level. The building resonant frequency of two- and three-story
houses, which prevail in the area, spans the range 4–11 Hz, with an average
value of 7.7 Hz. The danger of soil-structure resonance should be therefore
sought in this frequency range. Since the majority of Kobarid area is
characterized by lower (W part) or higher (E part) frequencies, the danger
exist mainly in a relatively narrow transition zone. |
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