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Great Rift Valley, Ethiopia
The Great Rift Valley of Ethiopia, (or Main Ethiopian Rift or Ethiopian Rift Valley) is a branch of the East African Rift that runs through Ethiopia in a southwest direction from the Afar Triple Junction. In the past, it was seen as part of a "Great Rift Valley" that ran from Mozambique to Syria.
==Description==
The Great Rift Valley lies between the Ethiopian Plateau to the north and the Somalia Plateau to the south. The rift developed as the Nubian and Somalian plates began to separate during the Miocene Period along the East African rift system. Rift initiation was asynchronous along the Ethiopian rift valley: deformation began around 18 million years ago at the south end, around 11 million years ago close to the Afar depression and probably around 6-8 million years ago in the central sector.〔Bonini M., Corti G., Innocenti F., Manetti P., Mazzarini F., Abebe T., Pecskay Z; ''The evolution of the Main Ethiopian Rift in the frame of Afar and Kenya rifts propagation,'' Tectonics, 24, TC1007, doi:10.1029/2004TC001680〕 The rift is extending in an ESE-WNW direction at about 5-7 millimetres (0.20-0.28 in) annually.〔Corti, G.; ''Continental rift evolution: from rift initiation to incipient breakup in the Main Ethiopian Rift, East Africa,'' Earth Science Reviews, v. 96, p. 1–53〕
The Ethiopian rift valley is about wide and bordered on both margins by large, discontinuous normal faults that give rise to major tectonic escarpments separating the rift floor from the surrounding plateaus. These faults are now thought to be inactive at the northern rift valley termination, whereas to the south they are still tectonically and seismically active.〔Keir, D., Ebinger, C.J., Stuart, G.W., Daly, E. and Ayele, A. ''Strain accommodation by magmatism and faulting as rifting proceeds to breakup: seismicity of the northern Ethiopian rift,'' Journal of Geophysical Research, 111(B5), B05314, doi: 10.1029/2005JB003748〕〔Agostini A., Bonini M., Corti G., Sani F., Manetti P.; ''Distribution of Quaternary deformation in the central Main Ethiopian Rift, East Africa,'' Tectonics, 30, TC4010, doi:10.1029/2010TC002833〕 The rift floor is cut by a series of smaller en echelon, right-stepping, rift basins of Quaternary to recent age. These basins are about wide and long. In the northern part of the rift, extension within the valley is now thought to be mainly along these faulted and magmatically active segments. These segments are considered to be developing mid ocean ridge spreading centers.〔Ebinger, C. J. and M. Casey; ''Continental breakup in magmatic provinces: An Ethiopian example,'' Geology, v. 29 no. 6 p. 527-530〕〔Corti, G.; ''Continental rift evolution: from rift initiation to incipient break-up in the Main Ethiopian Rift, East Africa,'' Earth Science Reviews, v. 96, p. 1–53〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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