In this paper, a novel strategy to generate broad-band earthquake ground motions from the results of 3D physics-based numerical simulations (PBS) is presented. Physics-based simulated ground motions embody a rigorous seismic wave propagation model (i.e., including source-, path-and site-effects), which is however reliable only in the long period range (typically above 0.75-1 s), owing to the limitations posed both by computational constraints and by insufficient knowledge of the medium at short wavelengths. To cope with these limitations, the proposed approach makes use of Artificial Neural Networks (ANN), trained on a set of strong motion records, to predict the response spectral ordinates at short periods. The essence of the procedure is, first, to use the trained ANN to estimate the short period response spectral ordinates using as input the long period ones obtained by the PBS, and, then, to enrich the PBS time-histories at short periods by scaling iteratively their Fourier spectrum, with no phase change, until their response spectrum matches the ANN target spectrum. After several validation checks of the accuracy of the ANN predictions, the case study of the M6.0 Po Plain earthquake of May 29, 2012 is illustrated as a comprehensive example of application of the proposed procedure. The capability of the proposed approach to reproduce in a realistic way the engineering features of earthquake ground motion, including the peak values and their spatial correlation structure, is successfully proved.

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The scope of this paper is to give an insight into the advantages of a new, allembracing, modeling approach of a strong ground motion scenario, by carrying out a source-to-structure analysis at regional scale, accounting explicitly for the uncertainties related to the databases and the models. To this end, a suitable case-study is represented by the 2007 Mw6.6 Niigata-Ken Chūetsu-Oki seismic sequence (west Japan), that damaged the Kashiwazaki Kariwa Nuclear Power Plant. This study describes the effect of the wave propagation path within the Earth's crust on the seismic response of nuclear reactor buildings located nearby a seismogenic source. The multiscale problem is de-coupled into three steps: (1) a parallel simulation of seismic-wave propagation throughout the Earth's crust at regional scale (≈ 60 km wide, major 3-D geological interfaces found below the nuclear site), reliable up to 5.0 Hz; (2) a mid hybridization step consisting in enriching the synthetic wave-field at high frequency (up to 30 Hz), employing an Artificial Neural Network to predict the short-period (SP) spectral ordinates; (3) a high-resolution structural dynamic analysis, introducing the hybrid broadband synthetics as input wave-motion. A simplified stress-test is performed, ✩ Fully documented templates are available in the elsarticle package on CTAN.

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