Within the framework of the CEC working group on the safety of thermal reactors a particular ad hoc subgroup was charged to investigate problems relating to the protection of NPPs against seismic effects.

Owing to the lack of an harmonized seismic data base in European countries and the existing differences in methods applied for the evaluation of seismic parameters, the ad hoc subgroup on seismic effects under the chairmanship of Mr. VAN GILS was charged to prepare an European catalogue of seismic data serving as the basis for the preparation of different seismic maps. This catalogue was revised by Mr. G. LEYDECKER to bring it to the present form.

These historical data are taken from an heterogeneous set of national catalogues, some of which are going back to before Christ. They all are harmonized as far as possible to the same intensity-scale (MSK-scale) to make them suitable for computerization. It is, however, obvious that the editors could only bring together what local seismologists have collected over a long time with intense engagement. National collections of so-called present-day data start at the beginning of the 20th century and include instrumental and macroseismic data. Based on instrumental data, the strength of an earthquake is expressed in terms of magnitude (Richter scale) while with macroseismic data the importance of a shaking is given in intensities (MSK-scale).

Such a compilation of seismic data can provide a basis for statistically supported studies of site selection procedures and the qualitative assessment of seismic risks. The rate of recurrence of seismic events in a certain region can e.g. be derived from the compiled data.

The European catalogue served as a basis for the preparation of seismic maps for EC member countries, Austria and Switzerland, which you will find in the appendix to the catalogue. Data for the years 1982 and 1983 are incomplete; these data are, therefore only listed but not plotted. Three groups of maps illustrate the content of the catalogue for different time periods and different intensities.

1. Time period 500 B.C. - 1981 A.C. for intensities equal or greater 8.5, 7.5, 6.5 and 5.5.
2. Shocks with intensities equal or greater 6.5 (beginning of small damages) for the time periods 500 B.C. - 1000 A.C, 1000 - 1799, 1800 - 1899. 1000 - 1899 and 1900 - 1981.
3. Shocks with intensities equal or greater 4.5 for the same time periods as under 2.

The maps give an impression of the beginning of data collection in the different cultures and show the enormous differences in the seismic risk for various regions in a conspicuous way.

The earlier report entitled "Catalogue of European earthquakes and an Atlas of European seismic maps" can be considered as an explanatory textbook to this catalogue and the maps; it was also prepared by Mr. J.M. VAN GILS and is already published as report EUR 11344.