A simplified method for determining the equivalent peak ground acceleration of near-fault pulse-like ground motions

Near-fault ground motions (NFGMs) differ significantly from far-field ground motions (FFGMs), as NFGMs exhibit pronounced pulse effects and directionality. Specifically, for a given earthquake event, the intensity level of NFGMs is generally higher than that of FFGMs due to less geometric attenuation. To ensure the seismic stability of engineering structures in near-fault regions, it is of vital importance to reasonably determine the ground motion amplitude of seismic actions in near-fault regions. Peak Ground Acceleration (PGA), as the core parameter for measuring ground motion intensity, is widely utilized to calculate equivalent seismic actions. However, current seismic design codes often lack consideration of pulse effects and directionality when determining the amplitude of ground motions in near-fault regions. To address this issue, this study analyzed 1,576 NFGMs records from the NGA-West2 database to quantitatively investigate the correlations between PGA, fault distance, and orientation. Through statistical regression, continuous calculation formulas for correction factors were derived. The results indicate that the fault distance correction factor ranges from approximately 1.2 to 2.0, and the direction correction factor ranges from 1.0 to 1.1. Ultimately, by integrating these factors, a simplified method for determining the equivalent near-fault PGA is proposed in near-fault regions for practical engineering design.