We propose a ground-motion prediction equation (GMPE) for probabilistic seismic hazard analysis of nuclear installations in Finland. We collected and archived the acceleration recordings of 77 earthquakes from seismic stations on very hard rock (VHR, i.e., the shear-wave velocity in the upper 30 m of the geological profile=2800  m/s according to the definition used in the nuclear industry) in Finland and Sweden since 2006 and computed the corresponding response spectra important for engineering evaluation. We augmented the narrow magnitude range of the local data by a subset of VHR recordings of 33 earthquakes from the Next Generation Attenuation for Central and Eastern North America (CENA) (NGA-East) database, mainly from eastern Canada. We adapted the backbone curves of the G16 equation proposed by Graizer (2016) for CENA. After the calibration, we evaluated the accuracy of the median prediction and the random error. We conclude that the GMPE developed can be used for predicting ground motions in Fennoscandia. Because of compatibility with the original G16 backbone curve and comparisons with the NGA-East GMPEs, we estimate that the formulation proposed is valid on VHR over the range of 2≤moment magnitude≤7.0 and 0≤ rupture distance ≤300  km, the depth range over 1.5–37 km, and frequencies between 1 and 100 Hz. The median of the composite prediction of the GMPE proposed was reasonable. The standard deviation of the prediction error (σ) was over the range of 0.73–0.86, in ln spectral acceleration units, for the relevant spectral frequencies. This is somewhat lower than the G16 σ, indicating lower aleatory variability. The new Fenno-G16 GMPE is applicable over a wider range of magnitudes than the two older GMPEs available in Finland and fits the data better, especially for peak ground acceleration and 25 Hz.

We present a modeling technique for generating synthetic ground motions, aimed at earthquakes of design significance for critical structures and ground motions at distances corresponding to the engineering near field, in which real data are often missing. We use dynamic modeling based on the finite-difference approach to simulate the rupture process within a fault, followed by kinematic modeling to generate the ground motions. The earthquake source ruptures were modeled using the 3D distinct element code (Itasca, 2013). We then used the complete synthetic program by Spudich and Xu (2002) to simulate the propagation of seismic waves and to obtain synthetic ground motions. In this work, we demonstrate the method covering the frequency ranges of engineering interests up to 25 Hz and quantify the differences in ground motion generated. We compare the synthetic ground motions for distances up to 30 km with a ground-motion prediction equation, which synthesizes the expected ground motion and its randomness based on observations. The synthetic ground motions can be used to supplement observations in the near field for seismic hazard analysis. We demonstrate the hybrid approach to one critical site in the Fennoscandian Shield, northern Europe.

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