Seismic Parameters Estimation In Northern Algeria

Résumé: Seismic hazard assessment studies, using a probabilistic or deterministic approach need a reliable earthquake catalog, covering a certain time period, seismogenic source model (line sources or area sources) and some seismic parameters, such as: the a and b values of the Gutenberg-Richter relationship, and the maximum «possible» magnitude expected in each source. This study is an attempt to develop seismic parameters estimation in northern Algeria. The seismicity analysis carried out is based on a reliable compiled earthquake catalog obtained from different agencies. All the intensities and magnitudes were converted to Ms magnitude using the most appropriate relationship among those we examined. The non-possonian events identified by means of the methodology proposed by EPRI which have been removed. Also, a simple procedure to identify aftershock events is discussed. The completeness of the final catalog has been discussed according to the procedure developed by Stepp, (1971). This check is a fundamental step to establish four complete and poissonian seismic models, which completely describe and characterize the seismic activity in northern Algeria. Seismic sources are delineated as in area by taking into account the most important geological features. Each seismic source is characterized by its seismic parameters, especially a and b values of the Gutenberg-Richter relationship, and the maximum expected magnitude. We estimate the a and b values by the procedure developed by Weichert, (1980), using the catalog of each zone. More attention is given to the estimation of the maximum expected magnitude using different statistical estimators (Kijko-Sellevoll, Gibowics-Kijko and Pisarenko). To avoid the abrupt change in the seismogenic source boundaries, these parameters, especially the b value and the maximum expected magnitude are smoothed over all the north of Algeria, this gives an overview of the spatial variation of these parameters in the studied area. For instance, the obtained estimated seismic parameters not only, give an appropriate overview and well characterizes the seismic activity in northern Algeria but also, are the most appropriate input parameters to the seismic hazard assessment.

Publié dans la revue: Bulletin du Service Géologique de l'Algérie