## 3 Procedure Considering Guidelines for Generating Ground Motions  
This study focuses on nuclear power plant structures as critical structures and is therefore subject to constraints imposed by relevant guidelines. The generation of ground motions for risk assessment involves the application of multiple guidelines related to the selection of ground motions based on the seismic intensity, spectral shape, and hazard de-aggregation. Owing to these complex considerations, the relevant criteria are somewhat unclear, and appropriate selection and conversion of recorded ground motions are necessary to generate input ground motions for risk assessment that match the shape and seismic intensity of the risk assessment spectrum. In this study, we propose a procedure to generate an input ground motion that matches the shape and seismic intensity of the risk assessment spectrum, using the recorded motion from regions with low to moderate seismicity where only low-intensity accelerograms are available. Figure 1 presents the procedure in a flowchart. As an example of this procedure, a simple PSHA was performed by selecting the optimal annual frequency of exceedance to evaluate the UHS as a spectrum for risk assessment. Based on the PSHA results, hazard de-aggregation was conducted to select ground motions appropriate for the UHS, and the scenario earthquake was identified, focusing on the magnitude-distance that contributed the most to the hazard. Since recorded ground motion data corresponding to the scenario earthquake are not available, a finite fault was modeled using the empirical Green's function method (EGFM) based on actual fault information from an existing earthquake event. An example of an earthquake event is the largest recent Mw 5.5 earthquake in Korea for which recorded ground motions exist [22]. This example earthquake was converted into the magnitude-distance of the scenario earthquake obtained from seismic hazard de-aggregation using finite fault modeling. The characteristic of the finite fault model using the EGFM is the generation of a diverse set of ground motion time histories for the same magnitude and distance. Therefore, it is necessary to analyze the spectral shape of the generated ground motions according to the spatial distribution from the EGFM and select the ground motion with a response spectrum similar to the risk assessment spectrum shape. In this process, a spectral shape considering the conservatism of the UHS is proposed. Ground motions were selected from two distinct target spectra to compare conservatism in a uniform hazard spectral shape. The two selected ground motions were considered as the seed motion of the input ground motion for the risk assessment. Spectral matching in the time domain was performed on the selected ground motions to ensure compatibility with the risk assessment spectrum. Finally, the impact of the target spectrum when selecting the ground motion in the spectral matching process was analyzed, and the selection conditions were presented in the input ground motion generation procedure for risk assessment.  
Based on the procedures applied at each step of the flowchart, ground motions that comply with each of the risk assessment guidelines can be generated using the recorded ground motions in low to moderate seismicity regions. Detailed descriptions of each step of the procedures depicted in the flowchart are provided in the following sections.