Publication Date:
2019-03-27
Description:
Site-effect assessments performed through earthquake-based approaches, such as the standard
spectral ratio (SSR), require good quality records of numerous earthquakes. In contrast, the
use of ambient noise appears to be an attractive solution for ease and rapid computation of
site responses with sufficient spatial resolution (microzonation), especially in low seismicity
areas. Two main approaches are tested here: the horizontal-to-vertical spectral ratio (HVSR)
and the noise-based SSR (SSRn). The HVSR uses the relative amplitude of the horizontal and
vertical components of the ambient noise. Instead, the SSRn defines the spectral ratio between
the seismic noise recorded simultaneously at a site and at a rock reference station, similar
to earthquake-based SSR. While the HVSR is currently used in hundreds of site-specific
studies, the SSRn approach has been gradually abandoned since the 1990s. In this study,
we compare the results obtain from these two approaches with those of earthquake-based
SSR. This comparison is carried out for two sedimentary basins, in Provence (southeastern
France) and in Argostoli (western Greece). In agreement with the literature, the HVSR does
not provide more than the fundamental resonance frequency of the site (f0). The SSRn leads
to overestimation of the SSR amplification factors for frequencies higher than the minimal
f0 of the basin (f0min). This discrepancy between SSRn and SSR is discussed, and appears
to be mainly dependent on the local geological configuration. We thus introduce the hybrid
standard spectral ratio (SSRh) approach, which aims to improve upon the SSRn by adding
an intermediate station inside the basin for which the SSR is known. This station is used in
turn as a local reference inside the basin for the SSRn computation. The SSRh provides site
transfer functions very similar to those of the SSR, in a broad frequency range. Based on these
results, the SSRn (or SSRh) should be further tested and should receive renewed attention for
microzonation inside sedimentary basins.
Description:
Published
Description:
1442–1454
Description:
5T. Sismologia, geofisica e geologia per l'ingegneria sismica
Description:
JCR Journal
Keywords:
Earthquake ground motions
;
Site effects
;
Seismic noise
;
Spectral ratio
;
04.06. Seismology
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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