The role of strike-slip faulting in the evolution of the Afar Depression from remote sensing data fusion, field investigation and radar interferometry

Remote sensing data integration, field studies and radar interferometry has proven to be an effective combination in evaluating the evolution of the Afar Depression, specifically, the interplay of normal and strike-slip faulting within the East Central Block. The Afar triple junction is a ∼200,000 km2 region of diffuse but complex deformation where the Red Sea, the Gulf of Aden, and the Ethiopian Main Rift meet. The Gulf of Aden and Red Sea rifts are currently propagating into the Afar Depression creating a ∼120 km long and ∼100 km wide overlap zone, known as the East Central Block. Field studies and fault plane solutions of seismic activity within the East Central Block have shown evidence of strike-slip movement along dominantly NW-trending faults. However, integrated radar and optical remote sensing data shows dextral, map-scale kink structures within the Tendaho Graben. Field studies provided additional evidence for dextral displacement along NE- to NNE-trending faults in the Tendaho Graben. Dextral strike-slip movement along NE- to NNE-trending faults are explained as tear zones within regions of localized lithospheric weakness as faulted blocks adjust to clockwise rotation of micro-blocks within the East Central Block. Differential Interferometric Synthetic Aperture Radar (DInSAR) characterizes the strain deformation within the East Central Block. Unwrapped interferograms and displacement maps show relative deformation patterns within and across micro-blocks that support a component of clockwise rotation about a vertical axis. Steep phase shifts along NW-trending faults with and without topographic expression indicate a change in the strain accommodation from preexisting fault scarps to newly formed fault planes. Steep phase shifts delineate NE-trending faults which exist within individual micro-blocks supporting tear zones as a means of accommodating the strain of clockwise rotating fault blocks. This work suggests that dextral strike-slip movement along NE-trending faults could be the cause of recent seismicity within the Tendaho Graben.