Recent seismotectonic stress regime of most seismically active zones of gulf of guinea and its kinematic implications on the adjoining sub-sahara West African Region

Abstract

The Tectonic stress regime of Gulf of Guinea region has been studied by stress tensor inversion analysis for the area bounded by latitude-10.00 S to 4.0oN and longitude-250 W to-11.00 E. A total of one hundred and four focal mechanism solutions, pertaining to the earthquake events which have occurred in this region, were used for this study. In order to decipher the stress pattern of this region, we have divided the region into four fracture zones namely Romanche, Chain-Romanche, Charcot and Ascension fracture-zones based on seismicity clustering, tectonics and available focal mechanism solutions. The seismicity pattern indicates that none of the nearby countries on the border line between the west Africa region and the gulf of Guinea is devoid of seismicity. Simultaneously, the stress tensor inversion in the four subzones of investigation indicates different types of stress orientations. All of these zones are characterized by varying principal axial directions. The orientation of the principal axial direction along Romanche, Chain-Romanche, Charcot and Ascension fracture-zones are along NE-SW, NE-SW, ENE-WSW and ESE-WNW respectively. The stress tensor inversion results indicate that Chain-Romanche, Charcot and Ascension fracture zones are characterized by extensional stress regime while Romanche fracture zone is characterized by strike-slip stress regime respectively. These patterns imply sea floor spreading activities in and around the mid oceanic ridges and the general orientation of the extensional stress regime is found towards the continents, along the line of migration / progression of earthquakes.