Chapter 11 Euroseistest 3D Array for the Study of Complex Site Effects K. Pitilakis, D. Raptakis, K. Makra, M. Manakou, and F.J. Chávez-García Abstract Euroseistest is currently the longest running instrumented test site in the world. It was originally defined as the 2D (N–S) cross section of the Mygdonian basin, N-E from Thessaloniki Greece, epicenter area of the M6.4 1978 earthquake. In this paper, we present the effort to extend the test site to a larger portion of the whole sedimentary structure, i.e., from 2D to a 3D structure. To this end we have compiled available geological and geotechnical information. We have analyzed microtremor and earthquake data. We present the results of the analysis of all avail- able information and data. The synthesis of all data allowed us to propose reliable image of the geometry and the properties of the basin. We have also obtained a reliable estimate of the site response throughout the basin and we have discussed several aspects of site effects in complex geologic structures, including the increase of spectral amplification compared to 1D site amplification. 11.1 Introduction Site conditions affect strong ground motion during destructive earthquakes. They have been shown to affect the intensity of ground motion by a value between one and two units (e.g. [4]). The importance of site effects led to the creation of test sites; sites where detailed observations on the variations of site response could be related to the subsoil structure. The first test sites were those of Turkey Flat USA [29] and Ashigara valley Japan [9]. In Europe, Euroseistest was established as a test site for seismology and earthquake engineering studies in 1993. During its operation, a large number of universities and institutes throughout the world have been involved in both field measurements and research studies. EUROSEISTEST project is actually a very powerful multidisciplinary European experimental site to perform integrated studies in earthquake engineering, engineer- ing seismology, seismology, and soil dynamics. It generates a set of high quality K. Pitilakis (B ) Department of Civil Engineering, Aristotle University of Thessaloniki, GR-54124 Thessaloniki, Greece e-mail: kpitilak@civil.auth.gr 145 S. Akkar et al. (eds.), Earthquake Data in Engineering Seismology, Geotechnical, Geological, and Earthquake Engineering 14, DOI 10.1007/978-94-007-0152-6_11, C  Springer Science+Business Media B.V. 2011