Développement d’un outil SIG d’estimation des dommages sismiques Cas de la ville de Tlemcen (Ouest Algérien)

L'Algérie est exposée au séisme, il est donc urgent de développer un outil de simulation et d’estimation de dommages sismique. Le but de cet article est d'estimer le risque sismique pour la ville de Tlemcen. Pour atteindre cet objectif, la méthodologie de simulation présentée dans le programme "HAZUS” en combinaison avec les systèmes d'information géographique (SIG) ont été utilisés. La ville a été divisée en plusieurs parties qui reflètent la typologie du tissu urbain qui à son tour n’est pas uniforme, puisque les structures modernes sont parfois situées à proximité des structures anciennes. L’événement sismique a été simulé en utilisant le catalogue algérien des failles actives. Les résultats obtenus montrent que les constructions les plus endommagées sont celles qui reposent sur des sols meubles.Mots-clés: SIG, risque sismique, probabilité de dommages, courbes de fragilité, Hazus. Use of a GIS tool for estimating seismic damage of the city of Tlemcen (Western Algeria) Algeria is exposed to seismic action, it is thus urgent to estimate seismic risk. The aim of this paper is to estimate the seismic risk for the city of Tlemcen. To reach this goal, the methodology of simulation presented in the program "HAZUS” together with the geographical information system (GIS) tools have been used. The city has been divided into multiple part that reflect the typology of the structure which is in turn not uniform since modern structure are sometimes located near old structure. The seismic hazard has been taken from the Algerian catalogue of active fault. The obtained results show that the most affected area is that located on soft soil.Keywords: GIS, Earthquake risks, probability of damages, fragility curves, Hazu

NEW INSIGHT IN THE DERIVATION OF AMPLIFICATION FACTOR BY TAKING INTO ACCOUNT SOIL PARAMETERS

International audienceIt is currently admitted that the amplification factor (AF) is one of the best tools to describe site effects. AF depends on soil parameters that are derived from the geometrical and mechanical soil properties of the soil profile. Thus, it is important to identify which soil parameters shape the form of the AF. The aim of this paper is to measure the effects of various site parameters on the variation of AF. As the problem is highly complex, a tool using the GRNN (Generalized Regression Neural Network) to understand which soil parameters have been developed. For a particular soil profile it has been found that values of AF derived from GRNN approach are closer to that of 1D linear viscoelastic seismic analysis particularly if the number of parameters increases. Based on this result a sensitivity analysis has been conducted to identify which parameters give good AF. For the practical case where we have to introduce only two parameters, it has been observed that the couple [resonance frequency (f 0) , time-averaged shear-wave velocity in the top 30 m (Vs30)] is the most interesting

Implementing effects of site conditions in damage estimated at urban scale

International audienceLocal site effects due to geotechnical conditions modify seismic motions on surface. This implies that during a given earthquake, buildings located on soft sites may experience a higher damage than similar buildings resting on nearby rock sites. The aim of this study is to provide an estimation of the influence of site conditions on the buildings damage distribution. We combine an approach adapted from the Hazus methodology for the assessment of building damage, with the Borcherdt non linear site amplification factors, that enable to characterize the high and low frequency amplification as a function of VS30 (the average shear wave velocity in the upper 30 m) and ground motion levels. Analysis of obtained results indicates that, seismic damage expressed by the normalized mean damage index depends not only on seismic shaking level and building typology but also on site conditions through the shear wave velocity proxy. A regression relationship is established between the seismic damage and both shaking levels and site conditions, aiming at presenting a simple, rapid tool for estimating this damage at urban areas. An index, the “damage increase ratio”, is proposed to quantify the increase of damage resulting from site effects, and its dependence on loading level and site conditions are quantified and discussed for the main building typologies present in Algeria. Depending on the building typology, the overall damage may vary within a range of 2–5 for moderate shaking (0.1 g) between hard rock and very soft soil, and within a range 1–1.5 for strong shaking (0.5 g). The reduction of the impact of site conditions with increasing shaking level is directly linked with the nonlinear soil behavior