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

Abstract

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 Mw 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 Mw 5.7 event, in agreement with local seismic recordings. Our models show that tectonic faulting accommodates 26 cm of extension corresponding 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.