Plate-boundary kinematics of the Afrera linkage zone (Afar) from InSAR and seismicity

Abstract:

Studying the mechanisms of interaction between rift segments is key to understanding the plate boundary kinematics of continental rifts. However, the spatial and temporal evolution of deformations at rift linkage zones are rarely observed directly. Here we combine all C-band InSAR data, from Envisat and Sentinel satellites, with local seismicity from the Afar rift of Ethiopia to investigate the plate-boundary kinematics of the Afrera linkage zone, the junction between the Erta Ale and Tat Ali rift segments in Northern Afar. We obtained average Line-Of-Sight InSAR velocities as well as time-series of cumulative displacements showing that deformation between the two segments is accommodated by a series of active en-echelon oblique faults striking ~NS. The faults at the western and central part of the linkage zone have a dominant east-dipping geometry while west-dipping faults occur in the east as the linkage zone approaches Tat Ali. Different fault behaviors are also observed: fault creep accompanied by low-level seismicity occurs at the linkage tips while the central faults behave in a stick-slip mode, associated with episodic seismicity (M_L > 5). Our results confirm that Afrera is a right-lateral linkage zone with dominant oblique NS-striking faults accommodating the extension between Erta Ale and Tat Ali. We show how different modes of deformation can occur with both creep and episodic seismicity characterizing different sectors of linkage zones.