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HOW WELL PREPARED IS ACCRA TO DEAL WITH AN EARTHQUAKE AND ITS AFTERSHOCKS? BY THEO ACHAMPONG.

HOW WELL PREPARED IS ACCRA TO DEAL WITH AN EARTHQUAKE AND ITS AFTERSHOCKS?

  1. Most recent earthquakes or tremors in Ghana are located along two major active fault zones, the Coastal Boundary Fault zone and the Akwapim fault zone. Accra sits at the intersection of these two major faultlines.
  2. The Akwapim fault runs northeasterly from the west of Accra through Kpong, Ho, and into Togo and Benin. On the other hand, the Coastal Boundary Fault forms the northern margin of the Keta Basin. To the west of Accra, the fault bends to strike east-west and intersects with the Nyanyanu fault in the Akwapim fault zone.
  3. A recent review of geological and instrumental recordings shows that earthquakes have occurred in the past and are still likely to occur within the vicinity of the intersection of the Akwapim fault zone and the Coastal Boundary Fault [Note: mostly in western Accra in the vicinity of the Weija-Gbawe enclave, including Bortianor, Amanfro, Weija, Sowutuom, etc.]. There are a number of other faults in the acute angle between these two major faults, the most important of which is the Weija fault striking west-northwest (WNW).
  4. Major shocks occurred in 1862 when every stone building in Accra was razed to the ground, and Christiansborg Castle and the forts were rendered uninhabitable. On 20 November 1906, Government buildings in Accra were damaged though no casualties were reported. Recorded minor shocks occurred in 1636, 1858, 1863, 1883, 1907, 1911, 1918-19, 1923, 1925, 1930 and 1933-35.
  5. The most destructive quake happened on 22nd June 1939, measuring 6.5 on the Richter scale. In that incident, 17 people were killed, 133 injured, and property damage was estimated at one million pounds. In recent years, more than 200 tremors have been recorded between 1998 and 2002, with magnitudes ranging from 1.0 to 3.0 on the Richter scale and intensities from 1 to 10.
  6. Accra is one of the most rapidly urbanising cities in all of Africa. The resultant effect of this urbanisation is (1) several shanty buildings being put all over the place, especially in Western Accra; and (2) metro and district assemblies unable to enforce building codes and standards, among others.
  7. Should the unthinkable happen (a strong to major quake of more than magnitude 6.0 on the Richter scale and accompanying landslides), I daresay many many people may die, and several others would be rendered homeless because of our lax and ‘fa ma nyame’ attitude of doing things. A magnitude 6.0 quake releases 60 million kilos of equivalent energy of TNT, while a 7.0 quake (like the recent one in Turkey will release about 20 billion kg equivalent of TNT). Note: Earthquakes are measured on the Richter Scale, which is a base 10 logarithmic scale. This scale measures the magnitude of an earthquake, which is the amount of energy it releases. For every single increase on this scale, the magnitude is increased by a factor of 10.

Source:Theo Achempong Facebook page.

Sources:
—Ahulu, S. T., Danuor, S. K., & Asiedu, D. K. (2018). Probabilistic seismic hazard assessment of southern part of Ghana. Journal of seismology, 22, 539-557.
— The Accra Earthquake of June 22, 1939. Nature 147, 751–752 (1941). https://doi.org/10.1038/147751a0
— Oteng-Ababio, M. (2012). Neglected vulnerabilities in a rapidly urbanizing city: reflections on earthquake risks in Accra. Journal of Housing and the Built Environment, 27, 187-205.

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