Προσδιορισμός της εδαφικής δομής με τη χρήση μικροθορύβου. Εφαρμογή στην εκτίμηση των δυναμικών ιδιοτήτων και της γεωμετρίας των εδαφικών σχηματισμών στη Θεσσαλονίκη

Abstract

It is widely recognized that local geological conditions have a large impact on ground motion at a given site. The geometry of the subsoil structure, the variation of soil types and its properties with depth, the lateral discontinuities and the surface topography are at the origin of large amplification of ground motion and have been correlated to damage distribution during destructive earthquakes (Aki, 1993; Bard, 1994; Faccioli, 1991; 1996; Chavez-Garcia et al., 1996; Pitilakis et al., 1999, 2001a, 2001b). Site effects estimation requires an adequate knowledge of the geometry and the dynamic properties of soil formations. Among the dynamic properties of soil deposits, the shear waves velocity (Vs) that defines the shear modulus (Go), is one of the most important parameter that controls the amplification of seismic motion. The knowledge of the dynamic properties, especially Vs velocity, and geometrical characteristics of soil formations allow the study of ground response and hence the assessment of the basic parameters for the aseismic designs of structures. Different aspects of site amplification from experimental and theoretical point of view were extensively discussed during all recent conferences such as 11th WCEE - Acapulco (1996), 11th ECEE - Paris (1998), ESG98 - Yokohama (1998) and 12th WCEE - New Zealand (2000). Issues like effects of irregular geological configurations, near field phenomena, basin edge and 2D effects are better understood and quantified as well. However, this kind of studies requires the ‘design’ of 2D sections that describe the geometrical and dynamic characteristics of soil formations independently of the depth of the rock basement. These aspects constitute the basic motives of the present thesis. The aim is to determine the geometrical and dynamic characteristics of soil formations, down to the rock basement, at Thessaloniki city, a densely populated and urbanized area.