Site Dependent Ground Response for the City of Patras, Greece

Results of a preliminary study of seismic ground response at different sites of the coastal city of Patras, in Southern Greece, are presented. At each site equivalent linear 1-D response analyses were conducted by using the finite element program LUSH 2. Values of dynamic properties of soils were obtained from either cross-hole tests or empirical correlations. The 'rigid base' excitation was selected as to best simulate the expected bedrock motions in Patras from local and distant earthquakes. The results of the analyses indicate a strong differentiation of seismic site response when moving from the coastal region of the city to the inland area. Peak surface accelerations were found to vary from 0.10 g in the coastal region to 0.50 g in the inland area, whereas the corresponding values of spectral acceleration ranged from 0.30 g to 2.0 g. Strong motion records obtained in the city during the July 14, 1993 MS = 5.4 Patras earthquake are in agreement with the results of this study. It is concluded that a systematic microzonation study of Patras would contribute to the seismic protection of the city.