Strain partitioning in the Natron Basin, East African Rift: Insights from geodetic and seismic moment rates.

The Natron Basin is located within the eastern branch of the East African Rift, a segment characterized by greater magmatic activity compared to the western branch. This activity has been shown to play a key role in accommodating deformation in the eastern rift, alongside crustal-scale faulting. The Natron Basin represents a particularly suitable natural laboratory to investigate the interaction between active tectonic and magmatic deformation, as previous studies have documented magmatic intrusion events associated with active rifting episodes in the region.

In this study, we use new geodetic observations acquired during a GNSS campaign conducted in the Natron Basin in summer 2025, and started in 2013, to investigate present-day deformation patterns. Campaign-derived horizontal (and vertical) velocities are used to estimate regional strain rates and to derive geodetic moment rates under standard mechanical assumptions. These geodetic estimates provide an integrated measure of ongoing extension across the basin.

To assess how this deformation is released seismically, we compare geodetic moment rates with seismic moment rates inferred from global earthquake catalogs, including NEIC and ISC; over comparable spatial and temporal scales. This comparison allows us to place bounds on the seismic coupling coefficient of rift normal faults.

The observed mismatch between geodetic and seismic moment rates suggest that a significant fraction of present-day deformation in the Natron Basin is accommodated though aseismic processes. These may include distributed crustal deformation and contributions from magma intrusions, which are known to influence rift evolution in magma-rich segments of the East African Rift. These observations illustrate the potential of combined geodetic and seismic analyses to investigate strain partitioning in magma-rich segments of continental rifts.