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

Abstract

Recent observations from geology, geodesy and seismicity at magma-rich continental rifts suggest that dike intrusion is the primary mechanism achieving plate extension (Ebinger et al., 2010;Sigmundsson et al., 2015;Wright et al., 2012). In these settings most medium-to-large magnitude, normal slip earthquakes are induced by dikes, while purely tectonic normal faulting is less common (Ebinger et al., 2010). For example, in the magma-rich rifts of Ethiopia (Afar and the Main Ethiopian rift) all the geodetically measured examples of normal faulting (i.e., since the onset of InSAR measurements in the area in 1994) have been induced by dike intrusion (e.g., Nobile et al., 2012;Wright et al., 2012).An earthquake sequence with a mainshock-aftershocks pattern occurred between 26 and 28 December 2022 in northern Afar (Bada region), with several earthquakes recorded globally. The National Earthquake Information Center (NEIC) recorded an earthquake M w 5.5 on 26 December at 12:21:07 (UTC), followed by a second mb 4.6 earthquake at 16:27:13 (UTC) on the same day, and a mb 4.9 at 16:14:57 (UTC) on 28 December (Figure 1). The European Mediterranean Seismological Center (EMSC) recorded the mainshock on 26 December with mb 5.2 and the second earthquake as mb 4.6, similar to the NEIC. On 28 December the EMSC recorded two earthquakes that were not detected by NEIC, both mb 4.5, at 14:02:27 (UTC) and at 14:35:19 (UTC), respectively, and later a mb 4.9 earthquake, the same as the M w 4.9 recorded by NEIC (Figure 1). The focal mechanism of the M w 5.5 earthquake calculated by the Global Centroid Moment Tensor (gCMT) project showed mainly normal faulting on a NNW-SSE striking plane, and with a minor component of strike-slip (Figure 1).

Tectonic and hydrothermal activity at the Yellow Lake fissure in response to the 2004 Dallol dyke intrusion event in Afar

“…North of Mount Dallol (Figure 1), a seismic swarm was recorded near Bada in December 2022, and interpreted as a consequence of plate spreading by pure tectonic extension (La Rosa et al, 2023). A seismic swarm had occurred at the same place in 1993 (Ogubazghi et al, 2004;La Rosa et al, 2023), and rupture propagation was found to be reminiscent of associated dike propagation (Ruch et al, 2021).…”