The United States Geological Survey recorded a Magnitude 5.2 Earthquake at a depth of 10 km, roughly 45 km to the west of the town of Fougamou in Ngounié Province, Gabon, slightly before 6.10 pm local time (slightly before 5.10 pm GMT) on Saturday 6 March 2021. There are no reports of any damage or injuries associated with this even, but it was felt across the west of Gabon.
Earthquakes are extremely rare in Gabon, which lies over Precambrian basement rocks which for the most part have not been tectonically active since the rifting which separated Africa from South America as the Atlantic Ocean in the Mesozoic. However, the North Gabon Sub-basin is cross-cut by a series of northwest-southeast trending faults associated with this Mesozoic rifting. Movement on these rift zones is now extremely limited, but the area is overlain by extensive evaporite salt deposits, which are structurally weak, and altering the way in which faults propagate.
Because salt deposits are dense and structurally weak, movement on faults below them does not typically propagate upwards though them. Instead, the salt layer will often expand laterally, accommodating the movement of the fault. Eventually, however, this displacement becomes to great for the overburden layer, which leads to the development of new faults in that layer, offset from the faults in the basement. Thus, gradual movements in the basement rock can be translated into sudden, shallow faulting in surface layers, which we experience as Earthquakes.
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