Full-length oceanic spreading in the Red Sea: Insights from the spatiotemporal distribution of earthquakes

The Red Sea is an embryonic ocean, offering a rare window into the early evolution of oceans. While the central-southern segment exhibits well-developed oceanic spreading, the tectonic regime of the northern Red Sea remains uncertain, specifically whether it still undergoes continental extension or has already transitioned to oceanic spreading. Thick sediment cover in the northern segment conceals direct evidence of oceanic crust formation. To address this, we examined the spatiotemporal distribution characteristics of more than10,000 earthquakes from a standardized International Seismological Centre (ISC) catalog (1960−2024). We found that seismicity is focused in a narrow zone along the Red Sea axis, and that the activity is overwhelmingly dominated by earthquake swarm sequences focused at distinct zones along the spreading axis. This pattern is typical of other (ultra)slow oceanic spreading centers globally, contrasting with the wider main shock−aftershock behavior expected in continental rifts. Furthermore, the seismological characteristics, including the spatial distribution of earthquakes, the typical swarm activity, and the overall b values, are comparable between the northern and central-southern segments of the Red Sea. We further found that earthquake swarms repeatedly occur in spatial association with bathymetric deeps, confirming these are active volcanic centers. This observation is also valid in the northernmost deeps despite the lack of exposed basaltic crust. Our comprehensive seismic analysis strongly supports the conclusion that active oceanic spreading extends along the entire length of the Red Sea.