EVALUATION OF PROBABILISTIC SEISMIC HAZARD IN NORTHERN ALGERIA. A CONTRIBUTION TO THE ALGERIAN BUILDING CODE M. Hamdache 1 , J.A. Peláez 2 , A. Talbi 1 and M. Mobarki 1 1 CRAAG, B.P. 63-Bouzaréah, 16340-Algiers Algeria, mhamdache@hotmail.com 2 . Department of Physics, University of Jaén, Jaén, Spain. japelaez@ujaen.es Abstract The recent seismic activity in northern Algeria evidences the need for updating the current Algerian building code, and consequently, the need to update the probabilistic seismic hazard values in force in northern Algeria assessed in previous works. The seismic risk reduction uses the results of seismic hazard analysis, and includes consequence and probability. This study is a large highlight on the used updated procedure. The spatially-smoothed seismicity approach was used for the computation of the seismic hazard values. The adopted method combines both zonified and non-zonified approches. It is well adapted to model disperse or background seismicity. Seismic hazard map in terms of peak ground acceleration (PGA) with 10% probability of exceedance in 50 years was initially obtained for rock. These maps are a crucial tools used in seismic risk reduction. Also, we have computed spectral acceleration (SA) values for rock, corresponding to soils type A in Eurocode-8, and soils type S1 in the Algerian building code, damped at 5% for different periods. The compilation of seismic hazard in term of SA at different periods, damped at 5%, for three different types of soils (rock, and soft and stiff soils), and for return periods of 100 and 475 years, allow us to derive interesting relationships between SA (0.2-sec) vs. PGA and SA (1.0-sec) vs. PGA independent of the considered return period. In addition, uniform hazard spectra (UHS) have been obtained for different return periods at different locations. The computed UHS for different types of soils and for a 475 years return period have been proposed as design spectra. We have used the well known Newman-Hall approach with certain modifications. The SA (0.2-sec) is used to establish the spectral region for lower periods (region controlled by acceleration), while the SA (1.0-sec) is used to establish the spectral region for intermediate periods (region controlled by the velocity), just as it is proposed in the most recent International Building Code. The results obtained in this study could improve the Algerian building code, which is a fundamental tool in seismic risk reduction. Key words: Peak ground acceleration, spectral acceleration, uniform hazard spectra, design spectra.