On the Limitation of the H/V Spectral Ratio Using Seismic Noise as an Exploration Tool: Application to the Grenoble Valley (France), a Small Apex Ratio Basin |
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| Authors: | Philippe Guéguen Cécile Cornou Stéphane Garambois Julien Banton |
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| Institution: | (1) Laboratory of Geophysics and Tectonophysics (LGIT), Joseph Fourier University of Grenoble, Grenoble, France;(2) Laboratoire Central des Ponts et Chaussées, Paris, France;(3) Institut de Recherche pour le Développement (IRD), France;(4) LIRIGM, University of Grenoble, Grenoble, France |
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| Abstract: | The H/V spectral ratio method based on seismic noise (HVSRN) was used in the Grenoble Basin (France), an Alpine valley characterized
by a small apex ratio. The resonance frequencies obtained in the experiments were compared to the thickness of the sediments
deduced from a microgravimetric survey and to the 1-D theoretical assessment of site responses. Given the abundance of data
on the sediments and depth of the basin, the values of the theoretical resonance frequency fo can be determined quite accurately. However, it has been observed that the effects of basin geometry can disturb fo measurements using the HVSR method, in particular for a case like the Grenoble Basin, which has a small apex ratio (w/H)
and strong suspected 2-D and/or 3-D effects. Interpretation of fo values in terms of bedrock depth gives rise to estimation errors of about 10% in certain cases, with the most significant
errors (>50%) occurring on the edges of the basin, where subsurface layers are characterised by larger heterogeneities and
where the basin topography is accentuated. This study suggests that great care must be taken when using the HVSRN method as
an exploration tool, at least in valleys with a small apex ratio. |
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| Keywords: | H/V ambient noise seismic response 3-D basin Grenoble |
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