Extensional Earthquakes in the Absence of Magma in Northern Afar: Insights From InSAR

In magma-rich rifts, normal faulting is commonly thought to be induced by dike intrusions. However, whether fault slip occurs purely tectonically is unclear. An earthquake sequence starting with a M-w 5.5 earthquake occurred in December 2022 in northern Afar, a continental rift near breakup. InSAR measurements show that seismicity was caused by normal faulting alone, without involvement of magma movements. Our best-fit InSAR models show that conjugate faults ruptured during the seismic sequence with mainly normal dip-slip and total deformation corresponding to a M-w 5.7 event, in agreement with local seismic recordings. Our models show that tectonic faulting accommodates 26 cm of extension corresponding to similar to 30 years of plate spreading without any link to magma. Our observations point toward significant along-rift variation in the proportion of extension from faulting, potentially caused by along-rift variations in rate of extension and/or from a spatially and temporally segmented supply of magma.