par Perton, Mathieu;Spica, Zack;Caudron, Corentin
Référence Geophysical journal international, 212, 2, page (930-941)
Publication Publié, 2018-02
Article révisé par les pairs
Résumé : The horizontal-to-vertical spectral ratio (HVSR) method has recently gained a resurgence of interest because of its new interpretation through the diffuse field approach. According to this theory, the HVSR measurement is linked to the Green's function retrieval. While the HVSR method is traditionally used to evaluate simple and shallow velocity model, we demonstrate that complex Earth' structure (that includes composite geological layering) can be assessed by choosing appropriate data processing and inversion scheme. In particular, we explore the effects of a strong lateral heterogeneity on the HVSR by using measurements along a vertical crater wall. However, wave propagation computation with lateral heterogeneity is inefficient to conduct an inversion. Then, to accelerate the forward calculation, we identified a simplified model consisting of an unbounded 2-D multilayer medium that allows describing the observed measurements with the use of a correction factor. The 2-D character comes from a nonstandard noise illumination related to the wind blowing perpendicularly to the crater walls. It is supported by several theoretical and experimental arguments.We also show that the H and V components can be retrieved independently, which may improve the sensitivity of the inversion at high frequency. To reduce the non-uniqueness of the problem,we consider the joint inversion of the H and HVSR's at several positions where the thicknesses of the layers were evaluated thanks to a large geological outcrop. The good agreement between the recovered velocity structure and the geology shows that the method is not limited to unbounded simple shallow structures, which opens the domains of application of the method to exploration geophysics or to hazard assessment.

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