The Afar Depression is located at one of the world’s most complex plate boundaries, where the Red Sea, Gulf of Aden, and the Main Ethiopian Rift meet in a triple-junction system linking continental and oceanic rifting. Although the Afar region is widely recognised as a key location for understanding the transition from continental extension to seafloor spreading, the relationships between fault growth, magmatism, block rotation, and the redistribution of strain remain poorly constrained at the surface scale. This thesis addresses this problem by providing an integrated zone-by-zone quantitative analysis of fault geometry, displacement, segmentation, linkage, cross-cutting relationships, and minimum apparent strain across three contrasting rift domains: the North Afar Depression (Zone 1), North Main Ethiopian Rift (Zone 2), and East Afar Depression (Zone 3).
This study combines manual fault mapping of 2,500 normal faults using 30 m resolution DEM map in QGIS environment with a suite of Python-based quantitative analyses of apparent fault length (L), apparent maximum displacement (Dmax), Dmax/L scaling behaviour, displacement-profile classification, segmentation and linkage metrics, and cross-section-based minimum strain calculations. These datasets are integrated with information from published geological maps and stratigraphic constraints to reconstruct the spatial and temporal evolution of deformation across the three zones. Analysis of Dmax and L data and log-log plots of Dmax/L show that across three zones, fault morphology population are consistent with a hybrid growth model.
The results show that Zone 1 is characterised by numerous short, low-displacement faults with mainly single- and multi-peak profiles, dominated by soft linkages and a southward increase in minimum strain along the southern Danakil margin, consistent with a structurally transitional rift sector in which strain has begun to localise but is still distributed across many mechanically immature, partly linked segments before migrating eastward into more axial Afar structures. Zone 2 is dominated by short, mechanically young faults within the central Wonji belt, where strain is tightly focused into a narrow NNE-trending magmatic rift and older border faults are now largely inactive. Zone 3 records the interaction between the Afar and Gulf of Aden rifts, combining Early Pleistocene grabens with very young Afar- and Gulf of Aden-aligned axial segments, producing a heterogeneous strain field linked to ongoing block rotation and extension relocation.
These findings provide new evidence confirming that the northern East African Rift and Afar Depression evolved as a diachronous, segmented triple junction rather than a simple
linear progression from continental to oceanic rifting. The combined patterns of fault maturity, strain localisation, and cross-cutting relationships are consistent with kinematic models that involve anticlockwise rotation of the Danakil Block and clockwise rotation of the internal Afar crustal blocks. More broadly, this thesis demonstrates that under the continental to oceanic rifting transition, strain can shift rapidly between neighbouring structural domains and that fault growth in magma-assisted systems is strongly influenced by resurfacing, magmatic intrusion, and block kinematics. These conclusions have implications for global models of rift evolution, the role of magmatism in strain accommodation, and the development of plate boundaries approaching continental break- up.
