Seismotectonic Stress Regimes of the Nubia-Eurasia Plates Boundary and Its Kinematic Implications on the Adjoining Region

Abstract

The tectonic stress regime of the Nubia-Eurasia plate boundaries and the adjoining region of the Strait of Gibraltar, Morocco, Azores-Cape St. Vincent, Algeria and Northern Algeria has been studied by stress tensor inversion analysis for the area bounded by latitude 27.00˚N to 40.00˚N and longitude 19.00˚W to 7.00˚E. A total of fifty-four focal mechanism solutions, pertaining to the earthquake events that have occurred in this region, were used for this study. The stress pattern of the different seismotectonic domains contained in this region was deciphered by zone-wise stress tensor inversion analysis of the Focal Mechanism Solutions (FMSs) through the algorithms of Michael and Gauss techniques. The stress tensor inversion in the five subzones of investigation shows different types of stress orientations. All of these zones are characterized by varying principal axial directions. The orientations of the principal axial direction along the Strait of Gibraltar, Northern Algeria, Algeria region, Morocco region and Azores-Cape St. Vincent zone are along N-W/S-E, NN-W/SS-E, N-W/S-E, NN-W/SS-E and N-S, respectively. The stress tensor inversion results indicate that the Strait of Gibraltar, Northern Algeria, Algeria region, and Azores-Cape St. Vincent zones are characterized by strike-slip tectonic stress regimes, while the Morocco zone is characterized by a thrust (compression) stress regime. The study concluded that for as long as the dominant compression axis of all the investigated subzones is virtually located along the N-S or along the convergent movements of the Nubia-Eurasia plates, the seismicity of the region shall continue to increase with the possibility of large magnitude events occurring anytime and anywhere within the investigated region. Hence, there is a need for precursory measures and preparedness for seismic hazards in the region.