The use of Rayleigh-wave ellipticity for site-specific hazard assessment and microzonation: application to the city of Lucerne, Switzerland

Abstract

S U M M A R YThe sediments underlying the city of Lucerne (Switzerland) consisting of fluvio-lacustrine deposits of Quaternary age have the potential to produce strong amplification of the seismic wavefield. To obtain a reliable estimation of the deep soil structure, we combine different methodologies based on ambient noise recordings, such as single station horizontal to vertical ratios and three-component array analysis. Two novel techniques to estimate Rayleigh-wave ellipticity from ambient noise recordings are tested. These are based on a single-and a multistation approach, respectively. The first utilizes the continuous wavelet transform to perform a decomposition of the noise wavefield and to isolate and extract the Rayleigh-wave contribution. The second, conversely, relies on a high-resolution f -k method to achieve the same result. We compare the results from the two techniques to provide an evaluation of their capabilities and limitations. A two-step inversion scheme is then presented to improve resolution on the bedrock depth. In particular, the surface wave dispersion information is initially used to constrain the soft sediment part, while the Rayleigh-wave ellipticity peak is subsequently used for constraining the bedrock depth. It is shown that such an approach is beneficial to map the bedrock geometry over dense urban areas. The output velocity model is then used to compute the local seismic amplification by means of gridded 1-D approximation.

A Bayesian Approach to Microtremor Array Methods for Estimating Shallow S Wave Velocity Structures: Identifying Structural Singularities

“…The FK method has the potential, in principle, to resolve the phase velocities of the fundamental mode and of higher modes, if any, but its resolution depends on the array geometry, the array size, properties of the wavefield of microtremors, and the data quality (Capon, ; Woods & Lintz, ). That sometimes makes it difficult to interpret the phase velocity estimates obtained (Poggi et al, ).…”

Seismic velocity structure of the Jakarta Basin, Indonesia, using trans-dimensional Bayesian inversion of horizontal-to-vertical spectral ratios

“…However, subsequent studies showed that the HVSR curve is closely linked with Rayleigh wave ellipticity (Lachet & Bard 1994;Lermo & Chavez-Garcia 1994;Fäh et al 2001Fäh et al , 2003. Failing to account for other, non-Rayleigh wave components of the ambient seismic noise can lead to an overestimation of the Rayleigh wave ellipticity (Poggi et al 2012;Hobiger et al 2013). Following the conclusions of the comprehensive review of the nature of the seismic ambient seismic noise wavefield by Bonnefoy-Claudet et al (2006), our assumption that the ambient seismic noise wavefield is dominated by the fundamental mode Rayleigh wave is supported by the proximity of the ocean, both the Java Sea to the north and the Indian Ocean to the south.…”

Guidelines for the good practice of surface wave analysis: a product of the InterPACIFIC project

“…the magnetic North) should be verified. The procedure for this verification is based on correlation analysis of the low-pass filtered horizontal components, rotated over different azimuths (see Poggi et al 2012 for a detailed description). This procedure may be particularly useful at sites where magnetic North cannot be accurately identified with a compass (influence of electric lines, railways, etc.…”