Today, surface-wave analysis is widely adopted for building near-surface S-wave velocity models. The surface-wave method is under continuous and rapid evolution, also thanks to the lively scientific debate among different disciplines, and interest in the technique has increased significantly during the last decade. A comprehensive review of the literature in the main scientific journals provides historical perspective, methodological issues, applications, and most-promising recent approaches. Higher modes in the inversion and retrieval of lateral variations are dealt with in great detail, and the current scientific debate on these topics is reported. A best-practices guideline is also outlined.

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Surface-wave analysis for building near-surface velocity models — Established approaches and new perspectives

This work focuses on the analysis of the multiple interactions between soil layers and civil-engineering structures in dense urban areas submitted to a seismic wave. To investigate such phenomena, called site–city interaction (sci) herein, two simplified site–city configurations are considered: a homogeneous, periodically spaced city and a heterogeneous, nonperiodically spaced city, both on a constant- depth basin model. These 2D boundary-element method models are subjected to a vertically incident plane SH Ricker wavelet. A parametric study of the city parameters (density of buildings and their natural frequencies) and the thickness of the basin is carried out to characterize the sci and to investigate its sensitivity to some governing parameters. The following parameters are analyzed: building vibrations, induced ground motion, ground-motion perturbations inside and outside the city, spatial coherency, and kinetic energy of the “urban wave field.” A so-called site–city resonance is reached when the soil fundamental frequency and structure eigenfrequencies coincide; building vibrations and ground motion are then significantly decreased and the spatial coherency of the urban field is also strongly modified. Building density and city configuration play a crucial role in the energy distribution inside the city.

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Seismic Site-City Interaction: Main Governing Phenomena through Simplified Numerical Models

SUMMARY The analysis of seismic wave propagation and amplification in complex geological structures raises the need for efficient and accurate numerical methods. The solution of the elastodynamic equations using traditional boundary element methods (BEMs) is greatly hindered by the fully-populated nature of the matrix equations arising from the discretization. In a previous study limited to homogeneous media, the present authors have established that the fast multipole method (FMM) reduces the complexity of a 3-D elastodynamic BEM to N log N per GMRES iteration and demonstrated its effectiveness on 3-D canyon configurations. In this paper, the frequency-domain FM-BEM methodology is extented to 3-D elastic wave propagation in piecewise homogeneous domains in the form of a FM-accelerated multi-region BE–BE coupling approach. This new method considerably enhances the capability of the BEM for studying the propagation of seismic waves in 3-D alluvial basins of arbitrary geometry embedded in semi-infinite media. Several fully 3-D examples (oblique SV -waves) representative of such configurations validate and demonstrate the capabilities of the multi-domain FM approach. They include comparisons with available (low-frequency) results for various types of incident wavefields and time-domain results obtained by means of Fourier synthesis.

https://hal.archives-ouvertes.fr/hal-00338211/document

A new fast multi‐domain BEM to model seismic wave propagation and amplification in 3‐D geological structures

3D soil structure of the Mygdonian basin for site response analysis

The geometrical and mechanical features of alluvial deposits have a major influence on seismic-wave propagation and amplification. However, for alluvial basins located in densely urbanized areas, the surface structures such as buildings could influence seismic-wave propagation near the free surface. In this article, the influence of surface structures on seismic-wave propagation is analyzed numerically in the case of an actual two-dimensional (2D) shallow basin. At a local scale, the vibration of a surface structure can induce a seismic wave field in the surficial soil layers. At the scale of an alluvial basin, the site-city models considered herein show that the city effect can lead to a significant seismic wave-field modification when compared to the free-field case. The coincidence between the fundamental frequencies of the soil layers and eigenfrequencies of the surface structures is a key parameter to investigate site-city interaction. When comparing simplified sitecity models (Kham et al., 2006) to the basin-city model, the influence of the lateral heterogeneities on the site-city interaction is found to be significant. Indeed, the seismic wave field radiated by the city appears to be trapped within the alluvial basin, and specific directivity features are found for this wave field. The influence of site-city interaction on the free-field seismic hazard may then be significant. The effects of the site-city interaction are beneficial in some parts of the city or detrimental in other parts (especially city boundaries). These effects strongly depend on the urban configuration (city heterogeneity, building density, etc.). Finally, the full characterization of the seismic wave field in densely urbanized areas could often raise the need for investigating site-city interaction and consider such parameters as basin and city fundamental frequencies, building density and city arrangement, as well as basin effects combined with the seismic wave field radiated by the city.

/pdf/seismic-wave-propagation-in-alluvial-basins-and-influence-of-za8go3vw8b.pdf

Seismic-Wave Propagation in Alluvial Basins and Influence of Site-City Interaction

https://hal.archives-ouvertes.fr/hal-00107884/document

M. Kham

Papers

Seismic Wave Amplification : Basin Geometry vs Soil Layering