Empirical spectral amplification functions using strong ground motion data and the mixed effect analysis method: application in Algeria

This paper aims to calculate empirical spectral amplification functions for multiple locations in the north central region of Algeria by utilising strong ground motion records of earthquakes occurring in this region (M ≥ 4). The analysis consists in performing a residual analysis of the observed ground motions in relation to the local ground motion prediction equation (GMPE). This task is achieved through the application of the mixed effect analysis method to divide the total residuals into between-event residuals (source effect) and within-event residuals (site effect). For instance, the reference site, situated on a rocky formation near the Keddara dam, shows clear deamplification for periods longer than 0.2 s with respect to the GMPE with Vs30 = 800 m/s. Furthermore, other sites located in urban areas within the Mitidja basin, such as Boufarik, display distinct amplification in the long-period range, which underscores the importance of considering basin effects within the Mitidja basin. Ultimately, based on the derived amplification functions, the local GMPE is adjusted by incorporating the site term. This modification aims to improve the accuracy of surface ground motion prediction in site-specific probabilistic seismic hazard analysis near the selected sites.