Development of a seismic source model for probabilistic seismic hazard assessment of nuclear power plant sites in Switzerland: the view from PEGASOS Expert Group 4 (EG1d)

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We present a seismogenic source model for site-specific probabilistic seismic hazard assessment at the sites of Swiss nuclear power plants. Our model is one of four developed in the framework of the PEGASOS project; it contains a logic tree with nine levels of decision-making. The two primary sources of input used in the areal zonation developed by us are the historical and instrumental seismicity record and large-scale geological/rheological units. From this, we develop a zonation of six macrozones, refined in a series of seven decision steps up to a maximum of 13 zones. Within zones, activity rates are either assumed homogeneous or smoothed using a Gaussian kernel with width of 5 or 15 km. To estimate recurrence rate, we assume a double truncated Gutenberg-Richter law, and consider five models of recurrence parameters with different degrees of freedom. Models are weighted in the logic tree using a weighted Akaike score. The maximum magnitude is estimated following the EPRI apporach. We perform extensive sensitivity analyses in rate and hazard space in order to assess the role of declustering, the completeness model, quarry contamination, border properties, stationarity, regional b-value and magnitude-dependent hypocentral depth.