Rift-parallel block-like motion of the graben floor during the 2005–2010 Afar rifting episode.

Crustal deformations associated with rifting episodes are often explained by both normal faulting and tensile opening in an elastic body, suggesting no significant rift-parallel displacements. In this study, using ALOS/PALSAR pixel-offset and multiple aperture interferometry (MAI) data, we detected ~1 m of northwestward block-like cumulative horizontal motion in the graben floor during the latter half of the 2005–2010 Afar rifting episode, Ethiopia. This horizontal block-like motion can be explained by additional shallower strike-slip on normal fault surfaces, which was presumably aseismic due to the very small number of strike-slip earthquakes and a significant gap between seismic and geodetic moment releases. We conclude that the rift-parallel movement can be interpreted by the strain accommodation of plate oblique spreading associated with dike intrusions, as has been demonstrated for the 2014 Bárðarbunga dike intrusion episode. Although we do not propose direct evidence for the plate oblique spreading, the complicated tectonic setting caused by the rotation of the Danakil block and the upwelling plume beneath the Afar triple junction may be drivers of the rift-parallel motion associated with the Afar dike intrusion. Unlabelled Image • Rift-parallel motions in the graben floor in the 2005–2010 Afar rifting episode. • Both PALSAR pixel offset and MAI data detect horizontal motion in the graben floor. • Block-like motion is explained by aseismic strike-slip on graben bounding faults. • The motion is interpreted by strain accommodation of oblique plate spreading. [ABSTRACT FROM AUTHOR]