The Main Ethiopian Rift: Ongoing deformation inferred from earthquake mechanism

The northern Main Ethiopian Rift (MER), which forms the northern part of the East African Rift System, offers an excellent tectonic setting to study the transition from continental to oceanic crust and also from tectonic to magmatic rifting. Opening of the rift started at 11 Myr ago. Until about 7 Ma, deformation was mainly accommodated at the rift border faults. Between 7 and 3 Ma, deformation migrated from the border faults to 20-30 km wide, 60 km long  magmatic segments. Earlier geodetic and field geological observations suggest that more than 80% of the present day opening of the rift is accommodated beneath these magmatic segments. On the contrary, recent observations indicate that deformation is more widespread than previously thought, with only 40% of the present day deformation being accommodated at the rift centre. 

 

Detailed understanding on the depth and epicentral distribution of earthquakes provides an important constraint on how strain is partitioned between the rift floor and border faults. Here I use high resolution earthquake catalogue and thermo-rheological modeling to constrain the active deformation patterns in the northern MER by assuming that the long term properties of the lithosphere represent the short term earthquake cycle. The final result of this study has significant implications for the location and magnitude of seismic hazard in the rift.