Geodetic study of an active rifting event in Afar, Ethiopia
Abstract
In September 2005, a 60-km-long dike intrusion took place in the Dabbahu-Manda Hararo rift (Afar depression in Ethiopia), a segment of the boundary between the Nubian and Arabian/Danakil plates. Since this major event, 13 smaller additional intrusions have affected the central and southern parts of the 2005 dike. Time-series from continuous GPS stations outside of volcanic regions show displacements due to these discrete diking events superimposed on constant-rate displacements after the main intrusion. These constant-rate displacements are up to seven times faster than the secular regional spreading rate of ∼16 mm/yr at GPS stations in the near-field (within 45 km of the dike), and up to three times at GPS stations in the far-field. We use a viscoelastic finite element model of the intrusion events to show that these far-field post-diking displacements are consistent with the relaxation of a weak mantle below a depth of 14 km with an average viscosity of 3.5x1018 Pa.s, in addition to the secular plate extension rate. This result, based on a significantly updated GPS data set, confirms previous results that post-diking deformation can be explained by a combination of discrete dike intrusions and viscoelastic relaxation triggered by the 2005 intrusion. However, a detailed analysis of the new GPS data set shows that displacements at sites located in the near-field of the Dabbahu-Manda Hararo rift require an additional process to take place. We use the residuals displacements (i.e., observed minus secular extension + discrete diking intrusions + best-fit viscoelastic deformation) to show that this newly identified surface deformation is most likely caused by the slow intrusion of a sub-horizontal sill-shaped magma body at shallow depth (∼3 km), with a constant inflation rate of ∼10 cm/yr.
Degree
M.S.
Advisors
CALAIS, Purdue University.
Subject Area
Geographic information science|Geophysics|Plate Tectonics
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