Evaluating the Effects of Input Parameters of the NGA-West2 Ground Motion Prediction Models on Record Selection Based on Conditional Spectrum Method

The NGA-West2 ground motion prediction models (GMPMs) are widely used to estimate shallow crustal ground motions at a given site based on several predictor variables such as earthquake magnitude, distance, and site characteristics. These GMPMs also play a key role in the construction of target response spectra for record selection. With the introduction of target response spectra such as the conditional mean spectrum (CMS) and conditional spectrum (CS) which are not only site-specific but are also structure-specific, there is a greater need for structural engineers to use GMPMs than before. However, many of the input parameters of GMPMs require having a strong knowledge of the seismicity of the site and, therefore, are often unknown to engineers. Engineers typically have to make assumptions to determine the unknown predictive variables such as dip angle, hypocentral depth, and rupture width which may affect the accuracy of the seismic performance assessment. In this study, the effects of these assumptions on record selection are investigated in terms of the spectral acceleration amplitudes and overall spectral shape of the CMS/CS target spectra. For this purpose, a parametric study is conducted by constructing a series of CMS/CS for a single-degree-of-freedom system based on the NGA-West2 GMPMs with different estimated source, path, and site parameters. Using these target response spectra, different sets of records are selected and compared. Also, the impact of the estimated predictive variables on the collapse capacity of the system is evaluated. It is found that the overall shape of the CMS/CS and the resulting selected records can be considerably affected by using the estimated input parameters when the exact values are not known. The significance of the effect of input parameters depends on the type of record selection method, the conditioning period, and the criteria of the earthquake causal parameters.