Modern seismic design codes and standards (e.g., ASCE 7–16, Eurocode 8, NEHRP, RPA, 2024) prescribe the use of the pseudo-acceleration (PSA) spectrum to determine seismic loads and forces. These codes provide spectral acceleration values for various structural periods to ensure buildings are designed to withstand earthquake forces. PSA is derived from the displacement response of a system, offering a theoretical approximation of seismic forces rather than a direct measurement of ground acceleration. Instead, it is computed based on the relationship between response displacement and natural frequency. In contrast, relative acceleration more accurately represents the actual motion of a structure during an earthquake, making it a more physically intuitive measure of seismic forces. However, PSA approximations introduce significant errors. This study analyzes acceleration and displacement response spectra for single-degree-of-freedom systems using a carefully curated dataset from the Pacific Earthquake Engineering Research (PEER) ground motion database across various site periods. Pseudo-response spectra were derived from horizontal displacement spectral ordinates, and differences between actual and pseudo-response spectra were examined. Based on this analysis, correction formulas were developed to improve PSA accuracy. The key findings of this study can be summarized as that the discrepancy between real and pseudo-acceleration spectra is significantly larger for near-fault motions than for far-fault records. Therefore, a conversion model that effectively adjusts PSA spectra, accounting for both distance and magnitude is proposed. Finally, the model’s validity is confirmed within the parameter limits of the used database.
