Comparative Study of the Seismic Hazard Assessments in European National Seismic Codes

The European Union has been promoting an homogenisation of the design rules for earthquake resistant structures through the Eurocode 8, which will soon become the official standard (CEN, 2003). However, the zonation for the basic earthquake ground motion will remain in the national authorities competence. Hence, it is important to outline differences and similarities in the `official' seismic hazard assessments (SHA) used by national seismic codes to define seismic zones and levels of seismic actions. The different SHA in 16 European countries were analysed taking into account a selection of comparative ingredients: date of the SHA, earthquake scale, definition of seismogenic zones, maximum earthquake estimation, attenuation relation, hazard calculation and hazard descriptor. Most of the official European SHAs were made more than 5 years ago, in terms of macroseismic intensity, taking into account seismogenic zones, estimating maximum earthquakes from historical records, making use of attenuation relationships for macroseismic intensity and assuming that earthquake occurrences follow a Poisson process. Most of the countries (11/16) depict hazard for a ∼475 year return period; seven of them use peak ground acceleration and four MSK intensity. There is also an important fraction relating the hazard to a different return period (3/16) or expressing it in a deterministic way (2/16). A general updating and homogenisation in many of the national SHA is recommended.