SEISMOTECTONICS IN THE REPUBLIC OF DJIBOUTI, LINKING THE AFAR DEPRESSION AND THE GULF OF ADEN

The Arta seismological array around the Gulf of Tadjurah monitored earthquake activity for over 15 years. Epicentral locations and focal mechanisms are compared with tectonic evidence from surface breaks, traces of active faults and the spatial distribution of swarms of aftershocks. Strike-slip motion on near vertical faults predominates. In the Gulf, left-lateral strike-slip on N150-degrees-E oriented faults is suggested, at variance with the emphasis in previous models on either: (1) a continuous plate boundary with spreading centres connected by ENE trending right-lateral transform faults; (2) a propagating rift oriented approximately east-west or (3) a few broad zones of extension between N150-degrees-E normal faults. Left-lateral, strike-slip motion occurring on a series of parallel faults results in clockwise rotation of the blocks between the faults. The type of deformation has similarities to that further west, but is not obviously controlled by a distinct pair of overlapping rifts, as proposed inland by Tapponnier et al. (1990). It is suggested that the stresses induced by the northeasterly drift of Arabia, alone, may deform the southern part of the more easterly oriented zone of lithosphere, derived of plume and ridge, which separates Arabia from Africa.