Comparison of propablistic seismic hazard studies within the oecd countries

Finland is situated in Fennoscandia on the Baltic shield, which is the one of the seismically quietest areas in the world. Nonetheless, Fennoscandia is an active seismic region, but at low earthquake recurrence rates and with relatively low magnitudes. Thus, the construction regulations in Finland do not require design against seismic events. Similarly, the Nuclear Power Plant is 1980s were not designed against seismic event. The seismic risks are assessed later and the current STUK (Radiation and Nuclear Safety Authority) requirements require the periodic seismic hazard assessment for old and new nuclear reactors and sites. The utilities have updated their hazard assessments with fluctuating results as the estimation of maximum magnitudes and derivation of attenuation functions is thus a challenge. The geological and geophysical data have been added and updated as well as the seismic catalogues for conceptual seismo-tectonic models and source area models, new ground motion prediction equations are fitted to new observations, and new probabilistic seismic hazard analysis (PSHA) have been carried out. In order to compare the seismic PSHA studies and their uncertainties an OECD/NEA project was launched in 2016. The Task Group of the OECD/NEA CompPSHA project developed and distributed a detailed questionnaire to screen the PSHA practices in the NEA countries with different seismic hazard levels. The purpose of this exercise was to try to understand what divergences exist in the PSHA methodologies applied, and if such divergences may explain the differences of PSHA outputs. The questionnaire was answered by eleven NEA countries with a very broad spectrum of seismic activity level ranging from very low (Finland, Sweden) to medium (France, Germany) and high (Japan). The purpose of the project was only to summarize and present the responses side-by-side, so that an informed reader may judge if certain methodological choices are substantiated within the context of each region. Given the diversity of geological and seismo-tectonic conditions in the responding countries such consensus is unlikely to be found. That being said the CompPSHA Task Group formulated the following general recommendations: • A threshold level for systematic procedure to survey relevant information regarding PSHA in the literature in the review period is needed. It is not suggested to update the hazard levels too frequently; on the contrary the Task Group acknowledges the need for stable operating environment for the plants. • The independent peer-review procedure should be employed for quality assurance and greater transparency. • Neighboring countries (examples around U.S./Canada and Central Europe’s administrative borders) should more coordinate the implementation and review of PSHA studies. Such practice could lead to better use of national resources and increase of quality and transparency of the studies. • As instrument to implement such recommendations, the continuous cooperation between the OECD/NEA Seismic Subgroup and IAEA External Events Safety Section (EESS) is encouraged. The immediate priority of the CompPSHA project is to extend the survey to non-NEA countries. Further harmonization of the details in PSHA practice is needed and could be done in dedicated Workshops. The final report “Comparison of PSHA in areas with different level of seismic activity” is submitted in October 2018 to the OECD for publication.