Thessaloniki's detailed microzoning: Subsurface structure as basis for site response analysis

The city of Thessaloniki is located in northern Greece, close to a large seismogenic area and it has experienced several destructive earthquakes during the present century, In this paper, we focus on the definition of the subsurface structure of the city from a site response analysis perspective. The paper presents, together with a summary of geology and seismicity, the results of a large-scale geophysical and geotechnical survey, in order to determine and validate geometry and dynamic properties of the main soil formations. The synthesis and combination of recent results regarding the dynamic properties with those obtained from the elaboration of a large database of classical geotechnical tests led to the design of a detail geotechnical map and of various 1-D profiles, 2-D cross sections and 3-D thematic maps for the main soil formations. These soil profiles and maps are oriented to site effect studies and provide a comprehensive picture easily adapted to geographic information systems (GIS) for planning and design purposes. Moreover, the results of this study were correlated with macroseismic observations reported in many earlier published microzonation studies of Thessaloniki. These comparative observations revealed the complexity of surface geology of the urban area, a fact which: is expected to provoke additional amplification with respect to 1-D resonance.