Seismic Wave Amplification in 3D Alluvial Basins: 3D/1D Amplification Ratios from Fast Multipole BEM Simulations

International audienceIn this work, we study seismic wave amplification in alluvial basins having 3D standard geometries through the Fast Multipole Boundary Element Method in the frequency domain. We investigate how much 3D amplification differs from the 1D (horizontal layering) case. Considering incident fields of plane harmonic waves, we examine the relationships between the amplification level and the most relevant physical parameters of the problem (impedance contrast, 3D aspect ratio, vertical and oblique incidence of plane waves). The FMBEM results show that the most important parameters for wave amplification are the impedance contrast and the so-called equivalent shape ratio. Using these two parameters, we derive simple rules to compute the fundamental frequency for various 3D basin shapes and the corresponding 3D/1D amplification factor for 5% damping. Effects on amplification due to 3D basin asymmetry are also studied and incorporated in the derived rules

Use of Bayesian Networks as a decision support system for the rapid loss assessment of infrastructure systems

This paper presents an approach for the rapid seismic loss assessment of infrastructure systems, where all probabilistic variables are modeled through a Bayesian Network (BN). While BN-based approaches have been introduced as promising tools for the risk assessment of systems, they suffer from computational issues (i.e., combinatorial explosion) that prevent their application to large real-world networks that require accurate and complex performance indicators. Therefore, a hybrid BN method is introduced here, where a preliminary Monte Carlo simulation is performed in order to generate a dataset of component damage configurations, which is used to build a simplified BN structure with only a few selected components. The most critical components are selected thanks to an unbiased importance measure computed from a random forest classification. While the proposed approach generates an approximate BN structure that cannot provide exact probability distributions of losses, the application of Bayesian inference in a retro-analysis context (i.e., updating of loss projections given field observations immediately after an earthquake) has a lot of potential as a decision-support system for emergency responders. This method is applied to a road network in France, where evidence such as recorded ground-motions or observed damages is used to update the state of the system. The approximate BN structure has the ability to include complex system performance indicators, such as the additional travel time accounting for traffic flows. A sensitivity analysis on the component selection method and on the number of selected components demonstrates the stability of the posterior distributions, even with very few selected components

Seismic Wave Amplification in 3D Alluvial Basins: Aggravation factors from Fast Multipole BEM Simulations

International audienceIn this work, we study seismic wave amplification in alluvial basins having 3D canonical geometries through the Fast Multipole Boundary Element Method in the frequency domain. We investigate how much 3D amplification differs from the 1D (horizontal layering) and the 2D cases. Considering synthetic incident wave-fields, we examine the relationships between the amplification level and the most relevant physical parameters of the problem (impedance contrast, 3D aspect ratio, vertical and oblique incidence of plane waves). The FMBEM results show that the most important parameters for wave amplification are the impedance contrast and equivalent shape ratio. Using these two parameters, we derive simple rules to compute the fundamental frequency for different 3D basin shapes and the corresponding 3D aggravation factor for 5% damping.Effects on amplification due to 3D basin asymmetry are also studied and incorporated in the derived rules

MODULATE: ANR project for the modeling of long period ground motions and the assessment of their effects on large-scale infrastructures

International audienceLarge-scale infrastructures are increasingly used in urban areas to meet the demands of continuously evolving societies. Recent seismic events showed remarkably that the construction of infrastructures with adequate seismic performance is the main factor in minimizing economic loss and long-term consequences to the communities. The modern design of large-scale structures, through the framework of performance-based earthquake engineering, requires consideration of the unique features of those structures, such as long natural period (> 2 seconds), interaction with the supporting soil, interaction with contained liquid, multi-support excitation, etc. In this project, we are concerned with the analysis, estimation and modeling of long period ground motions and their effects on the response of large-scale infrastructures such as high-rise buildings, liquid-storage tanks and long-span bridges. Intense long-period ground motions are usually generated at large distances from the source by large subduction-zone earthquakes and moderate-to-large crustal earthquakes. Such motions consist primarily of surface waves that arise when seismic waves encounter sedimentary deposits. One of the main objectives of the project is the development of a methodology based on the physics of surface waves, to describe the evolution of the spectral content of the ground motion for a site located in a sedimentary basin, and exposed to potential seismic sources, using relatively easily accessible input data. Furthermore, the stochastic description of ground motion will provide broadband realistic time histories that include basin-generated surface waves and which will be the means for practical assessment of the structural reliability and integrity of the considered large infrastructures. Realistic 3D numerical geological models will be implemented to study the physics of surface wave generation and propagation in sedimentary basins. The project is based on an inter-disciplinary effort with the synergy of Earthquake and Structural Engineers, together with Seismological and Numerical Modelling experts. The ultimate goal of the project is the development of novel, efficient and reliable tools and methods to be used by the earthquake engineering community for more robust and resilient designs of large-scale infrastructures