South-Central Section - 49th Annual Meeting (19–20 March 2015)

Paper No. 9
Presentation Time: 9:00 AM-4:00 PM


DEMISSIE, Zelalem S., BYRNES, Jeffrey and ABDELSALAM, Mohamed, Boone Pickens School of Geology, Oklahoma State University, Stillwater, OK 74078,

The Quaternary Dobe Graben in NE Ethiopia is situated in the intensely faulted east-central block of the Afar Depression that represents a triple junction. One of the most important unresolved questions in this region is how the strain is partitioned and localized, which is typically due to both spatial and temporal change. Understanding these changes requires a model that predicts the link between the geological processes and their genesis. In this paper, we resolved complete 3D time series displacements from Interferometric Synthetic Aperture Radar (InSAR) measurements for ~ 5 years. We first employed offset-tracking and multi-aperture InSAR techniques, with which the surface displacement in the azimuth direction can be measured together with the (line of sight) LOS displacement. The combination of multi-pass LOS and azimuth measurements integrated with GPS data revealed that the Dobe graben has experienced a clockwise rotation among individual fault blocks and confirmed the existence of the ongoing NE and SW remote stresses that cause an active differential extension. Results from persistent scatter and small baseline approaches shown that Dobe graben exhibits an asymmetrical full graben morphology but shows an almost mirror image LOS velocity and lateral displacement on both sides of the rift axis. In the middle, an average of 6.3 mm/year SE trending to 5.8 mm/year NW trending LOS velocity is shown. Furthermore, the high frequency changes seen in the displacement curves and large magnitude changes of velocity along a short distance of LOS measurement reveal the presence of sinistral strike slip faults near the center of the floor and along the Dobe relay zone. In the southern region of the Dobe graben, a maximum NW trending LOS velocity of 7.78 mm/ year toward NW and an opposite SE trending LOS displacement with 6.73 mm/year velocity near the graben center is observed. It should be noted that in this portion of the graben, a sharp, quick LOS polarity change can be seen and is interpreted as the presence of antithetic and synthetic blocks. The uplift and subsidence curves detect the gravitational slip and block rotation. Using InSAR data to model surface displacement allows us to calibrate conceptual kinematic models of the overlapping rift zones and understand the tectonic history of the African-Arabian plate boundary.
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