Seismic swarm activity at spreading centers in the southern Red Sea, Afar and Gulf of Aden

Abstract:

Rifting events periodically occur at divergent plate boundaries, consisting of magmatic intrusions, seismicity (seismic swarms), faulting and in some cases volcanic eruptions. Earthquake swarms occur at all types of plate boundaries but those observed at rift zones inland (Afar region, Iceland) and in a few cases offshore show a clear relation with magmatic intrusions. Despite the availability of global seismic catalogues since the late 60’s, only a few studies have focused on swarms in rift zones and on their tectonic and magmatic significance. These swarms typically last for a few days to a few weeks, lack a clear mainshock-aftershock decay pattern and are in some case related to submarine eruptions. Here we present a new study on seismic swarms in the southern Red Sea, Afar and Gulf of Aden region. We provide the first complete earthquake swarm catalogue for the region, integrating reexamined global and local catalogues with historical observations. We find that swarms have been re-occurring at the same locations in the southern Red Sea over decades suggesting the existence of local magmatically active spreading centers. For the region, the Gulf of Aden shows the highest swarm activity, followed by the Afar area and the Southern Red Sea. The later has seen the birth of two new volcanic islands during the past few years accompanied by seismic swarms. Both the eruption and the swarm activity indicate the presence of a magmatically active zone that has previously escaped notice.