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Seismic soil amplification in alpine valleys: a case study : the Rhône valley, Valais, Switzerland

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Defense Thèse de doctorat : Univ. Genève, 2000 - Sc. 3154 - 2000/03/31
Collection Terre et Environnement; 21
Abstract Alpine valleys are characterized by peculiar conditions, such as thick and young quaternary unconsolidated deposits (several hundred meters deep), steep slopes, rapid lateral variation of surficial deposit and a shallow water-table. In order to better appreciate the role of these elements on the seismic response, two areas were studied using different methodological approaches depending on the available data. In the Sion region, the soil amplification was evaluated in the frequency domain. Two-dimensional (2D) modeling and horizontal to vertical component (H/V) ratio on ambient seismic noise were independently used in order to cross-check their reliability and usefulness. Both techniques are consistent with the general trend, i.e. low frequency value where the deposit is thicker and higher values towards the edges where the sediment is thinning out. 2D modeling makes possible to demonstrate the influence of the asymmetry of the valley geometry, the importance of the slope gradient and the role of structure like shoulders on the amplification distribution. In the upper part of the Rhône valley, in the Susten-Brig area, the influence of local geologic conditions on soil amplification has been examined through a qualitative rating scheme. This approach not only integrates data on the surficial geology, depth to the water table, and thickness, but also on the slope gradient of the quaternary deposit because its influence on the amplification distribution has been demonstrated in the Sion region. The resulting relative maximum amplification map shows that the amplification distribution is mainly controlled by the steep slopes, although the level of amplification at a site depends on all of the present conditions. These results demonstrate the importance of considering not only the surficial characteristics but also the hidden morphological structure of a valley for a seismic hazard assessment in Alpine regions since both elements contribute to modify the seismic response of a site.
Keywords Seismic site effectsSeismic hazardMicrozoningH/V2D modelingRhône Valley
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Structures
Research group Reservoir Geology and Sedimentary Basin Analyses
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FRISCHKNECHT, Corine. Seismic soil amplification in alpine valleys: a case study : the Rhône valley, Valais, Switzerland. Université de Genève. Thèse, 2000. https://archive-ouverte.unige.ch/unige:26879

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Deposited on : 2013-03-20

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