Thesis defence : Valeria Soto Moncada

Numerical simulation of wave propagation in 3D basin models and their effects on nonlinear structures response

Sedimentary materials enclosed in basins modify the earthquake ground motion (EGM) characteristics by energy trapping, resonance and surface wave generation at the basin edge. Usually, these are defined as site effects and are considered by proxies associated with the one-dimensional (1D) structure beneath. In the context of hazard assessment with the Performance-Based Earthquake Engineering (PBEE) methodology, they are considered to modify the EGM in terms of an in-tensity measure (IM). The effects of the basin presence, i.e., the three-dimensional (3D) geometry, can be further approximated by aggravation or adjustment factors (AGF). This factor is traditionally defined as the ratio between the 3D and 1D cases of the IM computed with the horizontal components of motions using a plane wave approach. How-ever, the particular surface wave part of the ground motion, described with a more complex shaking, is never explicitly measured. This complexity comes specifically from the fact that surface waves are de-fined by low-frequency content and include both vertical and rotational components.With this regard, the current work assesses the impact of basin effects, with interest in surface wave generation, on the seismic damage of non linear structures. In order to introduce the complex input wavefield into the structure, numerical simulations are needed. In this case, a coupled 3D SEM-FEM approach is used, employing the Domain Re-duction Method (DRM). As a result, a complete-timewave propagation analysis from the earth quakesource to the structure can be investigated. There-fore, following the PBEE methodology, this modelis able to quantify and contrast the coupled basin effects simultaneously on the seismic hazard and structural demand analyses. As an initial step, in order to quantify the gen-erated surface waves correctly, a characterization based on the normalized inner product (NIP) is validated against other surface-wave-identification procedures. Then, the seismic hazard evaluation here is defined in terms of surface wave characterization and the AGFs. The study is carried out with parametric seismic scenarios, with simplified basin geometries and homogeneous material properties. Two types of seismic sources are simulated: plane waves with vertical incidence and deep and shallow double-couple point sources. In addition, the effect of the impedance contrast at the sediment- bedrock interface is also assessed. Moreover, to approach realistic scenarios, basin simulations of the Argostoli (Kefalonia island, Greece) and Cadarache (France) sites are investigated. Furthermore, the subsequent step of the PBEE methodology, regarding the structural and damage analyses, is performed using a nonlinear structure and the basin simplified case. The spatial variability is investigated by placing the structure in different positions, hence modifying the ground motion wave field arriving at the structure’s foundation. The results are further contrasted with those obtained from traditional methodologies to check if the fully coupled model from the source to the structure increases the seismic structural demand.

Composition of the jury :

•     Cecile Cornou, Directrice de recherche IRD, Université Grenoble Alpes - Reviewer
•     Panagiotis Kotronis, Professor, Ecole Centrale de Nantes - Reviewer
•     Etienne Bertrand, Directeur de Recherche, Université Gustave Eiffel - IFSTTAR - Examiner
•     Esteban Sáez, Associate Professor, Pontificia Universidad Católica de Chile - Examiner
•     Irmela Zentner, Expert research engineer EDF R&D - Examiner
•     Cédric Giry, Maitre de Conferences, Université Paris-Saclay, ENS - Examiner