Tensional fissures in sediments as signature of rift tectonics in the Main Ethiopian Rift

The Main Ethiopian Rift, which forms the northern part of the East African Rift, is a regime of extensional tectonics with geodetically measured mean spreading rate of 3.6 mm(yr)-1. Earlier studies have shown that the effects of this extension are manifested mainly through earthquakes, faults and volcanism. Recently, with the observations of the occurrence of fissures of tectonic origin on the sediment cover of the rift floor, an additional effect of the extensional process has been identified. The importance of this effect in characterizing rift tectonics could be commensurate with the areal size of the sedimentary cover of the rift floor which is substantial. The object of this study is to assess the significance of these tectonic-induced fissures as signature of the rifting process by comparing them to earthquake and volcanic activities. It is shown that fissures on sediments are significant indicators of rift tectonics with a corresponding role as agents of strain release. SINET: Ethiopian Journal of Science Vol. 23, No. 1 (June 2000), pp. 103-113 Key words/phrases: Earthquakes, fissures, sediments, signature, strain release, tectonics