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Abstract:
Topographic effects result from the influence of the surface geometry on the seismic ground motion and may generate strong amplifications, generally at hilltops and crests. They have caused significant damage during past earthquakes. They must therefore be accurately estimated even in areas of moderate seismicity. Despite numerous studies conducted over the last fifty years (Massa et al., 2014), the main parameters responsible for this phenomenon are not all identified, notably because of the difficulty in differentiating in recordings the effects of the surface geometry from others such as lithological site effects due to subsurface heterogeneities, faults, fractures and so on. Furthermore, topographic effects are mentioned in the Eurocodes8 in the form of simplified coefficients, independent of the frequency and subjected to interpretation. Therefore, topographical effects are rarely taken into account when generating site-specific response spectra. Thus, we propose to compare alternative approaches based on simple and easily accessible parameters. They are: - the FSC method developed by Maufroy et al. (2015) and - SuperTau method developed by the BRGM based on the previous French seismic regulation (PS92). Here, we firstly compare the estimations of topographical amplification computed by both methods for two case studies: the district of Menton in the south of France and the Dembeni site on the island of Mayotte. In a second step, we discuss how to consider topographic effects at these two sites in the associated response spectra.
