Re-appraisal of seismicity and seismotectonics in the north-eastern Algeria Part II: 20th century seismicity and seismotectonics analysis

The main objective of the research work is the homogenisation of the two recent Algerian earthquake catalogues for the common covered period of time, from 1900 to 1990, for the region under consideration limited by [33degreesN-38degreesN, 4degreesE-9.5degreesE] and the updating of the catalogue for the twentieth century ( 1900-2000). To mitigate the deficiency of the incompleteness of catalogue, an effort was made to establish a correlation between surface-wave magnitude Ms and body-wave magnitude m(b) in the form of Ms = a + b ( mb). A complete, exact and homogeneous earthquake catalogue as much as possible, comprising 870 seismic events, has been compiled. Seismicity analysis of the region shows a strong concentration of seismicity along a band of no more than 400 km width oriented mainly in the east-west direction parallel to the coast. Moreover, earthquakes in this zone are rather associated to strike-slip mechanism. The focal mechanism show a regional stress regime that corresponds to horizontal compression in NW-SE to N-S direction. As a result of the review of the seismicity of north-eastern Algeria from the compilation of checked and corrected data and its correlation with other geologic and geophysical investigations based on documentary sources, it was possible to construct a most complete seismotectonic map. It leads also to delineate four seismogenic zones in the Tellian Atlas, a less important zone in the Saharan Atlas, a sixth zone at the boundary of both Atlas and finally, a seventh one along the coastal zone. The seismicity-active faults correlation of some of these defined zones is examined in details with a special attention to the Saharan Atlas zone, the Hodna and Biban zone as well as Soummam and Babor zone where further research work allowed to find some neotectonic features considered as a significant sign of recent tectonic activity.