Site-to-bedrock over 1D transfer function ratio: An indicator of the proportion of edge-generated surface waves?

[1] We study multi-dimensional site effects in the small-size deep sediment filled basin of Grenoble (French Alps). A very dense array composed of 3-component seismometers over a 1 km aperture is used to investigate propagation parameters of waves propagating across the array. We present results for 6 teleseismic events for which we had a reference rock site. For the frequency range 0.1 to 1 Hz, records are clearly dominated by edge-generated surface waves. Quantification of energy carried by each identified wave train allows interpreting the difference between site-to-bedrock and 1D transfer function estimates in terms of laterally propagating basin-edge induced waves only above the fundamental resonance frequency of the basin. A simple ratio between site-to-bedrock and 1D transfer function curves should thus provide an estimation of the relative contribution of 1D and 2D/3D effects in ground motion on the condition that all the time signal length is taken into account.