Revealing 60 years of Earthquake Swarms in the Southern Red Sea, Afar and the Gulf of Aden

Abstract

Earthquake swarms occur sporadically at divergent plate boundaries but their recurrence over multiple decades and relation to magmatic spreading activity remain poorly understood. Here we study more than 100 earthquake swarms over a 60-year period in the southern Red Sea, Afar, and Gulf of Aden region. We first compiled an earthquake-swarm catalogue by integrating reexamined global and local earthquake catalogues from 1960 to 2017. This yielded 134 earthquake swarms that mainly cluster in 19 different areas in the study region, showing that in most cases swarms recur every few decades in the same area. The swarms exhibit a range of earthquake magnitudes and often include multiple M3 to M5 events with some swarms having occasional larger earthquakes over M6, primarily in southern Afar. Many of the earthquake swarms were clearly associated with rifting events, consisting of magmatic intrusions, surface faulting, and in some cases volcanic eruptions. Together, the swarms suggest that extension at these divergent plate boundaries occurs episodically along <100 km long segments, some of which were previously unrecognized. Within the study region, the Gulf of Aden shows the most frequent swarm activity, followed by Afar and then the southern Red Sea. The results show that the three areas were subject to an increase of earthquake-swarm activity from 2003 to 2013 in the form of three rifting episodes and at least seven volcanic eruptions. We interpret that the most likely controls on temporal variations in earthquake swarm activity are either temporal variations in magma supply, or rifting-induced stress change that trigger clusters of swarms.

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

“…Yellow lines are faults in the area of the 2022 sequence, orange dashed lines are fractures reported by Ruch et al. (2021). (c–e) wrapped co‐seismic interferograms for the initial part (c), later (d) part, and entire (e, f) seismic sequence.…”

The Energetic 2022 Seismic Unrest Related to Magma Intrusion at the North Mid‐Atlantic Ridge

“…Another very unusual aspect concerns the reported focal mechanisms. Thrust mechanisms are rarely reported at MOR (Ruch et al., 2021), where such failure type is incompatible with the dominant extensional stresses. The observation of large off rift thrust earthquakes during the 2022 is quite unique, likely requiring specific conditions.…”

“…Strike‐slip mechanisms with rupture planes oblique to the ridge axis, instead, can be triggered at the tip of migrating dikes and provide evidence for a magmatic driver (Hill, 1977; Passarelli et al., 2015). Finally, thrust mechanisms have been rarely reported in extensional domains (Ruch et al., 2021; Wolfe et al., 2012) and require a strong perturbation of the background, tectonic stress.…”

Morpho-tectonic Assessment of the Abu-Dabbab Area, Eastern Desert, Egypt: Insights from Remote Sensing and Geospatial Analysis

“…In fact, this assumption may not be an overinterpretation. Recent studies have shown that below the southern Red Sea, there is ongoing magmatic activity creating local earthquake swarms [63,64]. However, we would like to emphasize the need for further studies (e.g., tomographic imaging) to unequivocally infer the origin of seismicity in the Abu-Dabbab area.…”