Spatial and Temporal Evolution of Graben Formation During Rift Linkage Using Quantitative Geomorphology: Insights From Central Afar

Quantifying fault slip rates and resolving rift segment linkage mechanisms is important for understanding the evolution of magma-rich rift systems and the broader processes of continental break-up. In tectonically and volcanically active rifts, such as Afar, there is commonly a lack of quantitative, observational constraints on long-term fault system evolution and linkage. Quantitative geomorphology has proven effective in magma-poor rifts, yet its application in magma-rich contexts remains limited. In this study, we analyze 26 river catchments crossing active normal faults across seven major grabens in Central Afar. Using integrated geomorphic and topographic methods including stream power law analyses, knickpoint retreat metrics and swath profiles, we quantify landscape signals of tectonic activity and construct a spatial model of graben evolution. Our results show that rift linkage in Afar has been active for at least 3 Myr, with individual grabens accommodating extension over timescales of 0.5–1.0 Myr. Multiple grabens are commonly active synchronously, but integrating the graben initiation ages with their measured fault slip rate shows that most extension localizes through the center of the linkage zone. Notably, the Dobi Graben, in the center of the linkage zone, exhibits the youngest graben formation age and highest throw rates in the region of 0.4–0.8 mm/yr, implying it is the locus of present-day deformation. Our results provide the first quantitative constraints on spatio-temporal graben evolution in Central Afar, showing that extension due to rift linkage is primarily accommodated by en-echelon, normal fault-bound graben systems with the deformation progressively localizing through time.