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| Titel |
Detection of directivity in seismic site response from microtremor spectral analysis |
| VerfasserIn |
V. Gaudio, S. Coccia, J. Wasowski, M. R. Gallipoli, M. Mucciarelli |
| 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 ; 8, no. 4 ; Nr. 8, no. 4 (2008-07-25), S.751-762 |
| Datensatznummer |
250005647
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| Publikation (Nr.) |
 copernicus.org/nhess-8-751-2008.pdf |
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| Zusammenfassung |
| Recent observations have shown that slope response to seismic shaking can be
characterised by directional variations of a factor of 2–3 or larger, with
maxima oriented along local topography features (e.g. maximum slope
direction). This phenomenon appears influenced by slope material properties
and has occasionally been detected on landslide-prone slopes, where a
down-slope directed amplification could enhance susceptibility to
seismically-induced landsliding. The exact conditions for the occurrence of
directional amplification remain still unclear and the implementation of
investigation techniques capable to reveal the presence of such phenomena is
desirable. To this purpose we tested the applicability of a method commonly
used to evaluate site resonance properties (Horizontal to Vertical Noise
Ratio – HVNR or Nakamura's method) as reconnaissance technique for the
identification of site response directivity. Measurements of the azimuthal
variation of H/V spectral ratios (i.e. between horizontal and vertical
component) of ambient microtremors were conducted in a landslide-prone study
area of central Italy where a local accelerometric network had previously
provided evidence of directivity phenomena on some slopes. The test results
were compared with average H/V spectral ratios obtained for low-to-moderate
earthquakes recorded by the accelerometric stations. In general, noise and
seismic recordings provided different amplitudes of spectral ratios at
similar frequencies, likely because of differences in signal and instrument
characteristics. Nevertheless, both kinds of recordings showed that at sites
affected by site response directivity major H/V peaks have orientations
consistent (within 20°–30°) with the direction of maximum shaking
energy. Therefore, HVNR appears to be a promising technique for identifying
seismic response directivity. Furthermore, in a comparative test conducted
on a slope mantled in part by a deep-seated landslide we detected spectral
peaks with orientations close to the maximum slope direction, whereas no
evidence of directivity was found outside the slide boundaries. This
indicates the influence of the landslide body on seismic response
directivity. |
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