Reports: ND849600-ND8: Spatial and Temporal Variations of Crustal Deformation in the Afar Depression: Constraints from Radar Interferometry

Stephen S. Gao, PhD, Missouri University of Science and Technology

Mohamed G. Abdelsalam, PhD, Missouri University of Science and Technology

Rupturing of continental lithosphere through the transitioning from continental rifting to sea floor spreading and the onset of passive continental margins has been a central question where the academic and petroleum industry communities have spent appreciated efforts addressing it. Understanding the evolution of these widespread structures has received significant attention from the petroleum industry community because these structures are sites of sediments accumulation where ~60% of all hydrocarbon resources are discovered. In this study we used remote sensing data to investigate present-day crustal deformation in the central Afar Depression of Ethiopia, where a transtion from continental to oceanic rifting is currently going on.  We have successfully determined the current deformation field in our study area. In addition, we have also measured suface deformation associated with active volcanoes in Afar. 

1. Crustal deformation in central Afar

Crustal deformation of East Central Block in the Afar Depression of Ethiopia and Djibouti was measured using the Envisat satellite, Advanced Synthetic Apeture Radar (ASAR), C-Band data to create ascending and descending interferograms. Data used in this study  were collected over different time sequences between 2002-2010 over the East Central Block, which is hypothesized to be the location of the Nubian-Arabian plate boundary in the Afar Depression. Strain localization is expected to be manifested by a high phase change. For the East Central Block, 2 Pass + DEM interferometry was utilized to create 22, cm scale phase displacement maps, from 21 ASAR scences. In addition, mean surface velocity maps in cm/yr was create using 3-Pass + DEM interferometry for ASAR data from 2007, 2008, and 2009. Only master and slave pairs that had suitable perpendicular baselines (>500 m) were processed.

About 2 cm of vertical Displacement can be seen on the northeastern border fault of the Dobe Graben and the Data Yager Hanle Border fault in an ASAR pair collected from 10/12/2007 and 10/31/2008. In general, high phase change in the vertical displacement maps is concentrated in the Data-Yager Hanle-Dobe, Der Ela’ Gaggade, North Bahlo grabens and the southeastern Siyarrou Block. The eastern and southeastern portions of the East Central Block are likely undergoing the most crustal deformation. The Arabian-Nubian plate boundary in the Afar will likely follow a deformation pathway in the southeastern ECB. InSAR measurements from 2007-2010, have a maximum of ~5-6 cm/yr with 2 Pass DInSAR (2005-2010). A mean surface velocity map collected from 3 ASAR scenes from 2007, 2008 and 2009 shows that the vertical deformation in the East Central Block is ranges from -4.2 to 4.2 cm/yr.

2. Using InSAR to detect actively deforming volcanoes in the Afar Depression

For this study, four Envisat ASAR scenes were selected based on having the best coverage of volcanoes in the Afar Depression. The four scenes allowed for study of over 30 volcanoes. The main coverage areas include ther Erta Ale Complex, Nabro range, Dabbahu region of the Red Sea propogator and the central Tendaho Graben. Deformation was detected at Erta Ale, Dabbahu and the central Tendaho. The Nabro range did not exhibit any mean deformation. These results were combined with work by H. Carrie Bender for an abstract that was submitted for the Geological Society of America annual meeting in Minneapolis, MN, USA. Our results show that the volcanoes associated with the active propogators displayed significant deformation during the 2004-2010 interval studied while the transverse ranges exhibited little to no mean deformation.