3D configuration of Mygdonian basin and preliminary estimate of its site response

Abstract

Euroseistest is currently the longest running test site in the world. It was originally defined as the 2D cross-section of the Mygdonian basin going from Profitis to Stivos villages. In this paper, we present the first results of the effort to extend the idea of test site to a larger portion of the whole sedimentary structure, i.e. the extension of the idea of Euroseistest from a 2D to a 3D structure. To this end we have compiled available geological and geotechnical information. We have analyzed microtremor and earthquake data recorded seven years ago, that had not been thoroughly exploited. We present the results of the analysis of H/V spectral ratios from microtremors recorded at 195 sites, and from earthquake records at 14 stations. The results are validated through comparison with the well studied 2D cross-section. In addition to this, the geometry of the edges of the basin has been deduced from electrical tomographies. The synthesis of all these data allowed us to propose reliable map of dominant frequencies throughout the basin, a good constrain on the geometry of the basin at the edges, and shear-wave velocity profiles at some points. Our results indicate that average shear-wave velocity is not constant throughout, and thus the dominant frequency map is not a faithful image of the geometry of the basin. We have also obtained a reliable estimate of the site response throughout the basin. The results have been used to plan an additional measurement campaign, and are currently used to compute site response using a 3D seismic modelling code. We expect that the usefulness of Euroseistest to understand site effects in 3D geological structures will be as large as it has been in its 2D phase.