Wednesday’s incident was an earthquake, not just a tremor – Geological Survey Authority

What was believed to be an earth tremor on Wednesday evening was actually an earthquake, according to Ghana Geological Survey Authority.

Nicholas Opoku, a senior Seismologist at the Authority, said the earthquake had a magnitude of 4.2 on the Richter scale and described it as a mild earthquake.

"This is a small earthquake. If you are moving from 4.5 to 6.0 [on the Richter scale], you are moving into a moderate earthquake. Then from 6.0 going, you are moving into a bigger one," Mr. Opoku explained on the Citi Breakfast Show.

He noted that the epicentre of the earthquake, which was felt outside the Greater Accra Region, was "between Dansoman towards Bortianor."

The foreshock of the earthquake was measured at 3.7 on the Richter Scale, the mainshock registered at 4.2 on the scale and the aftershock was the weakest measured at about 3.5 on the scale.

In the past few years, environs of Accra have been hit by a series of earth tremors of magnitudes ranging between 2.6 and 3.9.

The most recent was in March 2019 which had a magnitude of 3.9.

Some of the areas that experienced the tremors at the time included Gbawe, Sowutuom, Old Kasoa Barrier, New Bortianor, Awoshie, Abelemkpe, Tabora, Achimota, Ablekuma, Kissiman, Westland, Laterbiokorshie, Legon and McCarthy Hill.

Mr. Opoku, at the time, predicted that these seismic incidents would get worse.

After the March 2019 tremor, the Ministry of Interior inaugurated a 10-member committee to develop a comprehensive programme for national earthquake preparedness and response.

The committee, chaired by an engineer, Carlien Bou-Chedid, was expected to finish work by April 15, 2019.

In November 2019, earthquake guard equipment was installed at the Weija-Gbawe Municipal Assembly.

Ghana's history with earthquakes

Records indicate that the earliest earthquake in Ghana occurred in 1615 with magnitude greater than 6.0 on the Richter Scale.

There are records noting that an earthquake in 1636 caused havoc in several parts of Axim in the Western Region.

The last three major earthquakes occurred in Ghana in 1862, 1906 and 1939.

The 1862 Accra earthquake had a magnitude of 6.5 on the Richter Scale and caused three fatalities in addition to the damage to property.

Magnitude 4.6 and 4.9 seismic events also occurred in Accra in 1871 and 1872.

The epicentre of the 1906 earthquake was near Ho collapsing buildings and causing severe damage.

The June 1939 magnitude 6.5 earthquake, which was centred around James Town, was the most destructive in Ghana's history, causing an estimated $67.3 million damage at the time.

This seismic event lasted about thirty seconds and killed 17 people and injured about 140 persons.

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