Site Amplification Assessment in the East Corinth Gulf Using 3D Finite-Difference Modeling and Local Geophysical Data

Elastic 3D wave-field simulations were performed in the seismically active region of Eastern Gulf of Corinth, in the area of Loutraki city. A new methodology was tested with the aim of performing multiple simulations for a large variety of realistic sources located around the study area, by employing 3D finite-difference modeling using matrix operations for the calculation of the spatial velocity and stress derivatives. The new methodology was proven to be quite efficient in simulating the near surface 3D site effect of the study area, by greatly minimizing the simulation time, thus allowing the use of 3D finite-difference modeling for a large number of simulations. The complex geological features of the study area were obtained by performing multiple passive MASW surveys within the busy urban area of Loutraki. By processing the acquired geophysical data, a highly inhomogeneous near surface velocity structure in the study area was obtained and was implemented in the 3D wave-field simulations. The near surface amplification that is caused by the 3D subsurface structure was proven to be highly significant for the area of Loutraki, with high spectral amplification compared to the amplification that is caused by an equivalent 1D model in the area. The dominant frequencies of the spectral amplification for the 3D model were also confirmed by Processing HVSR measurements that were also taken in the area. Finally, we also investigated how the propagation direction affects the near surface amplification.