University of Pretoria: West Africa should prepare for strong earthquakes, UP scientists warn

A powerful earthquake of magnitude 6.5 hit Accra, Ghana, in 1939. It is still considered the most powerful earthquake to have hit West Africa, killing 22 people and injuring close to 200. While rare, scientists at the University of Pretoria (UP) are using new data and modern techniques to help predict when such an earthquake could strike that side of the continent again.

Professor Andrzej Kijko, Director of UP’s Natural Hazard Centre, recently helped create one of West Africa’s seismic hazard maps. However, he says important information about earthquake hazards in the sparsely populated region has been incomplete because of a lack of high-resolution earthquake detection networks.

“We know very little about the seismicity of Africa. In China, we have a catalogue more than 4 000 years old. However, reliable instrumental data for Africa only goes back about 70 years, or 100 years if you consider the strong earthquakes that have been recorded,” Prof Kijko says.

While the region has seen its fair share of significant earthquakes, such as the 1984 magnitude 6.4 earthquake in Guinea, scientists still don’t know enough about the seismic nature of West Africa to predict the impact of the next quake reliably. As West Africa gears up to develop critical infrastructure, seismic hazard data becomes essential for critical infrastructure plans.

“If another magnitude six earthquake were to occur, it would cause tremendous damage to infrastructure, and so a seismic hazard assessment is needed for engineers to properly design structures,” he says.

To conduct a seismic hazard assessment for a specific area, researchers need to know the past earthquakes in a region and the near-surface structure of the earth’s crust at that location. Prof Kijko and his team used data from the International Seismological Centre and local seismic stations to assess the seismic hazard and settle an old debate about the region’s seismicity.

They found that West Africa can be called a stable continental region (SCR) instead of a region of shallow crustal seismicity, as some researchers believe. The result implies that West Africa should expect strong earthquakes from time to time, which can cause significant damage that threatens economic activity.

“Researchers are changing their opinions about this region as more information becomes available,” he says.

The work of a seismic hazard researcher is never done, as new information becomes available and accepted ideas become overturned. Prof Kijko says there are still significant knowledge gaps across the African continent that need to be filled with more seismic hazard assessments.

“Earthquakes are rare and everybody relaxes and lives peacefully until a strong earthquake, like the 2006 earthquake of magnitude seven in Mozambique, hits,” he says. This 2006 quake hit Mozambique so strongly that it caused damage as far-afield as Durban in South Africa, and is considered one of the strongest events to have ever occurred in Africa.

“This all shows that our knowledge of the seismicity of Africa is very limited, and we need more research if we want to sleep in peace,” he says.

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