A magnitude 6.0 quake struck the Gulf of Aden at 21:07 UTC, 10 km down

A magnitude 6.0 earthquake struck the eastern Gulf of Aden at 21:07:38 UTC on 27 August, which was just after midnight on 28 August in Aden and Caluula. The U.S. Geological Survey and GEOFON both published Mw 6.0. Depth estimates sit between 10 and 18 kilometres. GEOFON’s confirmed solution places the epicentre at 13.27 degrees north, 50.54 degrees east, with a 10-kilometre depth and a later moment-tensor depth of 17 kilometres.

EMSC puts the same origin 204 kilometres east-southeast of Mukalla in Yemen, a city of about 258,000, and 152 kilometres north-northwest of Caluula in Somalia. Other distance notes in circulation read 145 to 146 kilometres off the Somali coast and 209 kilometres southeast of Mukalla. The scatter is ordinary for an offshore event. All of the numbers keep the rupture in the water, not under a city.

What the fault said

GEOFON’s moment tensor gives nodal planes of 114 degrees strike, 35 degrees dip, rake minus 74, and 275 degrees strike, 55 degrees dip, rake minus 100. That is a normal-faulting solution, the kind expected on a spreading centre. The Gulf of Aden is the plate boundary between Arabia and Somalia. It opened as Arabia pulled north-east away from Africa and is still extending. A shallow normal earthquake of this size is the boundary doing what the textbooks say it does.

GFZ was cited by some regional desks at 6.2. The reviewed international consensus settled at 6.0. Forty stations contributed to one of the public solutions, with a magnitude error near 0.05. Status on the GEOFON page is confirmed.

Who felt it

Population-exposure models estimated about 66,000 people in light shaking and about 1.09 million in weak shaking. Maximum intensity in those models is IV on the Modified Mercalli scale, which is light. The USGS PAGER alert for fatalities and economic loss is green: low likelihood of casualties and damage. The same product notes that many buildings in the wider region are low-rise nonductile concrete frames with infill, a type that fails in stronger shaking. This event did not deliver that shaking on land.

Tsunami risk was described as low. Earthquakes below about 6.5 in this setting rarely move enough seafloor to build a wave of concern. No tsunami warning was the operational outcome. By Friday afternoon no damage reports had come out of Mukalla, Caluula, Bereeda or Bosaso.

Yemen’s Seismological and Volcanological Observatory Center in Dhamar is on the EMSC contributor list, alongside USGS, BGS, Geoscience Australia and a long string of other agencies. That is the quiet fact of a well-recorded oceanic event: the waveform is public, the mechanism is public, and the human consequence so far is a night of light shaking on two shores of a busy shipping lane.

The Gulf of Aden carries tanker and container traffic between the Red Sea and the Arabian Sea. A 6.0 under the water column does not close the lane. It does add one more dated point on the spreading axis. For civil defence desks in Hadramawt and Puntland the file can stay on the green list unless an aftershock sequence changes the numbers.