Inundated by calls, the city’s emergency management agency told residents not to worry.
“There is no likelihood of an earthquake disaster in Nigeria,” it said, as the country “is not in an earthquake zone”.
Days later, another government agency – the National Space Research Development Agency, which runs the Centre for Geodesy and Geodynamics – announced that the tremor was 3.0 in local magnitude and 2.6 in moment magnitude.
Local magnitude is the same as Richter magnitude and measures how much the ground vibrates during an earthquake. Moment magnitude measures the energy released by the movement of rock along a fault in the earth’s crust.
But is the emergency agency right that there is “no likelihood” of a major earthquake? Not quite.
Nigeria’s earthquake history
Earthquakes with a local magnitude lower than 5.0, known as tremors, were usually not destructive, Prof Adekunle Adepelumi, a seismologist at the Obafemi Awolowo University in Ile-Ife, told Africa Check.
“At least 32 tremors have been recorded since 1919,” he said. “Nigeria cannot be referred to as an earthquake-free zone. The recent tremor, which we named tremor Mary, shows that the subsurface of Abuja is unstable, contrary to previous assumptions.”
Adepelumi was a member of a presidential committee set up to study September’s Abuja tremor. The committee concluded that earthquakes were a potential hazard in Nigeria and identified five towns most at risk – a significant shift from the narrative that an earthquake disaster was unlikely.
The director of the Centre for Geodesy and Geodynamics, Dr Tahir Yakubu, said the epicentre of tremor Mary, Abuja’s Mpape district, lies in a weak fault zone. Yakubu also served on the presidential committee.
While Mpape and Kwoi are both in northern Nigeria, the south of the country has also had its share of shocks. On 11 September 2009 a tremor shook towns across states in the southwest, including Abeokuta, Ijebu-Ode and Ibadan.
Adepelumi and Yakubu were among seven seismologists who studied the 2009 tremor. Their report indicated that its cause, a fault zone underlying the region, was linked to fracture zones in the Atlantic Ocean.
Mining, water extraction and other causes
In reaction to tremor Mary, the government suspended all mining activities in the affected area. The assumption was that the tremor was nothing more than vibrations from rock blasting.
The presidential committee said about 110,000 boreholes had been sunk in Abuja, a city of some 8,000 square kilometres. These pumped “about 330,000 metric tonnes of water” out of the earth every day, causing an underground void that put the region at risk of tremors.
Another probable cause of quakes in Nigeria is oil and gas operations, Ross Stein told Africa Check. Stein is an adjunct professor of geophysics at Stanford University and scientist emeritus at the US Geological Survey. He runs Temblor Inc, a tech company that helps people estimate their seismic hazard and lower their earthquake risks.
“Some of the recorded quakes are associated with the oil and gas fields of the Niger delta,” he said. “This suggests that they could be induced earthquakes.”
Stein said the US state of Oklahoma had experienced shocks of up to magnitude 5.8, triggered by oil and gas drilling, and this could be the case in southern Nigeria. Such shocks can cause major damage to poorly constructed buildings.
William Seelig, a science information officer at the US Geological Survey, said the risk was present everywhere. “Essentially, there is nowhere on the planet that can be deemed an ‘earthquake-free zone’,” he told Africa Check.
So what’s the chance of a big bang?
Adepelumi has predicted that a major earthquake could hit Nigeria between 2020 and 2028, based on quake records since 1919. But others said this was far from certain.
“Earthquakes cannot be predicted in terms of time, place and magnitude,” Stein told Africa Check. “However, the likelihood can be forecast but these probabilities will be very small over a limited time, place or magnitude range.”
Seelig said the probability of an earthquake of a certain magnitude anywhere was largely based on historical quakes and tremors, and how close the region was to an active fault in the earth’s crust.
“Probabilities and forecasts are rather like climate probabilities and weather forecasts, while predictions are more like statements of when, where, and how large, which is not yet possible for earthquakes,” US Geological Survey website explains.
But Nigeria has only 18 active seismic stations to measure vibrations in the earth, Adepelumi said. This means the country “has a lot of ground to cover in terms of early detection and recording of the earthquakes”.
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