Definition of subsoil structure and preliminary ground response in Aigion city (Greece) using microtremor and earthquakes

An extensive campaign—including detailed geologic and geotechnical surveys both existing and news as well as noise measurements—was conducted along a cross-section in order to define both geometry and soil properties (mainly the shear wave velocity) of the main formations in Aigion city. Aigion city is located in the Gulf of Corinth, Greece, a highly seismic region of the Aegean Sea. The main objective of the accurate 2D soil model is its use in site response modeling and in the interpretation of observations from a vertical down-hole accelerograph array. This model revealed a complex geologic structure with a multi-faulted shear zone related to the Aigion fault. The defined subsurface structure offered the possibility for its correlation with estimated site effects, in terms of spectral ratios. Two different data sets, earthquakes recorded at down-hole accelerograph network and noise measurements at 17 sites, were used. To translate the empirical transfer functions with the geologic structure, the 1D estimates were also computed. All these results are consistent, indicating a satisfactory correlation between the soil model and preliminary site response.