Ground zoning against seismic hazard in Athens, Greece

The 1999, Ms=5.9, Athens earthquake caused serious structural damage to buildings in the western part of Athens, Greece. This paper presents the ground zoning against seismic hazard proposed shortly after the earthquake in order to aid reconstruction of the area. Existing engineering geological and geotechnical data were combined with local observations to provide a unified set of classification criteria, consistent with provisions of the Greek Seismic Code EAK. The accuracy and the possible limitations of this zoning procedure are addressed through comparison with observed damage distribution as well as results from seismic ground response analyses performed at sites with well established soil profiles. There is clear evidence that the proposed zones correspond to geological formations exhibiting grossly different seismic response with regard to the design of common engineering structures. However, the mostly qualitative nature of the guidelines for ground categorisation provided by EAK and the general lack of systematic, site-specific geotechnical data for the whole area induce uncertainties in the definition of the seismic design actions for the different zones. These objective uncertainties certainly demand increased conservatism but do not limit application of the proposed methodology for first aid, preliminary planning in the event of destructive earthquakes.