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A seismogenic zoning for north Algeria is proposed. The characteristics of each zone are studied in detail and different statistical analyses are performed in order to assess the slope of the Gutenberg-Richter relationship, the mean annual activity rate of earthquakes, the average return period, the probability of non-exceedence during a time period and the maximum expected magnitude. The slope of the Gutenberg-Richter relationship determined by traditional methods, physical strain energy release and corresponding magnitude, together with a new approach based on both historical and instrumental data, are used to estimate the seismic hazard parameters.The seismic hazard parameters obtained described well the characteristics of each proposed seismogenic zone. The b-value of the Gutenberg-Richter relationship concurs especially well with the most common seismotectonic interpretation of each zone, for example 0.70 9 0.06 at El Asnam region and 0.639 0.09 around Algiers. The average return period obtained (approximately 300 years for magnitude 7.5 at El Asnam region, exceeding 1000 years in other regions), corroborate those obtained through Paleoseismic studies and others using a digital elevation model.

In this study, the procedure of the earthquake hazard evaluation recently developed by KIJKO and SELLEVOLL (1992) is used to estimate seismic hazard parameters in the northern part of Algeria. The new method differs from the conventional one because it incorporates the uncertainty of earthquake magnitude, and accepts mixed data containing large historical events and recent complete catalogue. The importance of the method lies in its ability to estimate from incomplete and uncertain data files the parameter b of the Gutenberg-Richter relationship, the annual activity rate u of event and the maximum possible magnitude m max . In this method, the earthquake process is considered to be of the Poisson type with an annual activity rate u, and with a doubly truncated exponential distribution of earthquake magnitude with parameter i.The northern part of Algeria is subdivided into three zones. For each zone, estimation of b-value, the annual activity rate u and the expected maximum magnitude are obtained. The mean return period and the probability of non-exceedence of some magnitude during a time period T =50 and 100 years are computed.The results obtained in this study using this methodology, give a prior picture of seismic hazard in the northern part of Algeria. In some regions (Mitidja and Chelif basins) these results corroborate not only with the observation, but also with seismotectonic results.

This study examines distinctive features of ground motion parameters in northern Algeria. An initial computation of seismic hazard in terms of horizontal peak ground acceleration (PGA) and spectral acceleration (SA) at different periods, damped at 5%, is carried out for three different types of soils (rock, stiff soils and soft soils) for return periods of 100 and 475 years. In addition, uniform hazard spectra (UHS) are computed for these two return periods at several locations in the region. Then, the UHS computed for different soil types are proposed as a starting point to define elastic design spectra for building-code purposes. We have used the well-known Newmark-Hall approach. As proposed in the most recent International Building Codes, the SA (0.2 s) value is used to establish the spectral region for lower periods (region controlled by acceleration), whereas the SA (1.0 s) value is used to establish the spectral region for intermediate periods (region controlled by velocity). We also obtained important relations, dependent on site condition, between SA (0.2 s), SA (1.0 s) or SA max values, and the PGA, for both return periods of 100 and 475 years. Other relationships between PGA or SA max values have also been derived for return periods of 100 and 475 years, in this case independent of site condition.

Seismic hazard in terms of spectral acceleration (SA) has been estimated for the first time in northern Algeria. For this purpose, we have used the spatially-smoothed seismicity approach. The present paper is intended to be a continuation of previous work in which we have evaluated the seismic hazard in terms of peak ground acceleration (PGA) using the same methodology. To perform these evaluations, four complete and Poissonian seismic models have been used. One of them considers earthquakes with magnitudes above M S 6.5 in the last 300 years, that is, the most energetic seismicity in the region. Firstly, seismic hazard maps in terms of SA, at periods of 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, 1.5 and 2.0 sec, with 39.3% and 10% probability of exceedance in 50 years, have been obtained. Therefore, uniform hazard spectra (UHS) are computed and examined in detail for twelve of the most industrial and populated cities in northern Algeria. All the reported results in this study are for rock soil and 5% of damping. It is noteworthy that, in the seismic hazard maps as well as in the UHS plots, we observe maximum SA values in the central area of the Tell. The higher values are reached in the Chleff region (previously El Asnam), specifically around the location of the destructive earthquakes of September 9, 1954 (M S 6.8), and October 10, 1980 (M S 7.3). These maximum values, 0.4 g and 1.0 g, are associated with periods of about 0.2 and 0.3 sec for return periods of 100 and 475 years, respectively.