Reading landscapes from Afar: Field-based geomorphic constraints on fault evolution in the Dobi Graben, Ethiopia

Resolving fault evolution in time and space for magma-rich rifts remains a challenge, particularly at the scale of individual fault systems where fault growth, volcanism and surface processes interact. Central Afar, Ethiopia, is widely recognised as a key natural laboratory for investigating active continental break-up and the interactions between surface processes and fault activity. This is particularly true within the structurally complex rift linkage zone between the Dabbahu-Manda Harraro and Asal magmatic segments of the Red Sea and Gulf of Aden rift systems, respectively. Previous studies and numerical models based on geodetic data, strain-rate analyses and paleomagnetism have provided important conceptual insights into the wider tectonic architecture and mechanisms of strain transfer across this zone. However, direct structural constraints and quantitative field-based measurements of fault initiation ages are limited, and fault evolution histories based on systematic observational data are unresolved.

In this study, we characterise the chronology of graben development within the rift linkage zone by integrating quantitative geomorphic analyses with new field datasets from the Dobi Graben. Our initial DEM-based regional-scale geomorphic analysis of river long profiles and swath profiles indicate that the Dobi Graben is among the youngest and most tectonically active structures in the linkage zone, characterised by its high throw rates of ca. 1 mm/yr. Building on this, we focus on two river catchments that cross the main Dobi Graben bounding fault to better resolve its temporal evolution history and fault kinematics. We combine new field measurements from these catchments, including geomorphic and hydraulic parameters, Schmidt hammer measurements of bedrock strength, and grain size estimates, with high-resolution topographic analyses to trace the growth and evolution of the main Dobi Graben through time, and to quantify transient river response to active faulting.

These data place refined, field-based constraints on bedrock strength and erodibility allowing lithological and surface process controls on landscape dynamics to be explicitly accounted for, in addition to the tectonic forcing. Relationships between knickpoint migration, channel steepness and catchment morphology are used to better constrain river incision rates and fault growth patterns, enabling a clear reconstruction of the Dobi Graben fault evolution history. In doing so, our study provides clear and detailed insights into the role of the Dobi Graben in accommodating extension within the Central Afar rift linkage zone in the last 1 My and advances our understanding of major fault kinematics and rift linkage dynamics in an active continental rift.