In 1990, present day

South Sudan South Sudan (; din, Paguot Thudän), officially the Republic of South Sudan ( din, Paankɔc Cuëny Thudän), is a landlocked country in East Africa. It is bordered by Ethiopia, Sudan, Central African Republic, Democratic Republic of the C ...

was rocked by a series of violent earthquakes. It started with the largest event, a 7.2, and continued with multiple very large aftershocks for the next couple of months. It contains some of the largest recorded earthquakes anywhere in Africa.

Tectonic setting

The

East African Rift System East or Orient is one of the four cardinal directions or points of the compass. It is the opposite direction from west and is the direction from which the Sun rises on the Earth. Etymology As in other languages, the word is formed from the f ...

(EARS) is a system of rifts and associated

rift lakes The Rift Valley lakes are a series of lakes in the East African Rift valley that runs through eastern Africa from Ethiopia in the north to Malawi in the south, and includes the African Great Lakes in the south. These include some of the world's ...

within the eastern portion of the African continent. It accommodates the internal breakup of Africa. It is a boundary between the Somali and

African Plate The African Plate is a major tectonic plate that includes much of the continent of Africa (except for its easternmost part) and the adjacent oceanic crust to the west and south. It is bounded by the North American Plate and South American Plat ...

. The

Victoria Victoria most commonly refers to: * Victoria (Australia), a state of the Commonwealth of Australia * Victoria, British Columbia, provincial capital of British Columbia, Canada * Victoria (mythology), Roman goddess of Victory * Victoria, Seychelle ...

and Rovuma microplates help accommodate additional more local stresses. The eastern portion of the rift runs from the Afar rift to

Tanzania Tanzania (; ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa within the African Great Lakes region. It borders Uganda to the north; Kenya to the northeast; Comoro Islands and ...

, while the western portion runs from

Lake Albert (Africa) Lake Albert, originally known as Lake Mwitanzige and temporarily Lake Mobutu Sese Seko, is a lake located in Uganda and the Democratic Republic of the Congo. It is Africa's seventh-largest lake, as well as the second biggest of Uganda's Great La ...

Uganda }), is a landlocked country in East Africa East Africa, Eastern Africa, or East of Africa, is the eastern subregion of the African continent. In the United Nations Statistics Division scheme of geographic regions, 10-11-(16*) territor ...

all the way down to

Mozambique Mozambique (), officially the Republic of Mozambique ( pt, Moçambique or , ; ny, Mozambiki; sw, Msumbiji; ts, Muzambhiki), is a country located in southeastern Africa bordered by the Indian Ocean to the east, Tanzania to the north, Malawi ...

. The Aswa Rift Zone (ARZ) is an important geologic structure in the area near the earthquakes. The ARZ may act as a broad zone of faulting that links together the eastern and western portions of the EARS. The mainshock occurred along a fault where the ARZ and EARS meet.

Earthquake sequence

May 20 mainshock

The first and largest earthquake in the sequence struck near

Juba Juba () is the capital and largest city of South Sudan. The city is situated on the White Nile and also serves as the capital of the Central Equatoria State. It is the world's newest capital city to be elevated as such, and had a populatio ...

at 02:22:01 on May 20, 1990. The event had a of 6.6, with a and of 7.2, and struck at a depth of . Its

focal mechanism The focal mechanism of an earthquake describes the deformation in the source region that generates the seismic waves. In the case of a fault-related event it refers to the orientation of the fault plane that slipped and the slip vector and is ...

shows left-lateral (sinistral) strike-slip faulting, which is consistent with the shear forces in the area of the ARZ. The event killed 31 people and damaged some buildings in Juba, and some in Moyo, Uganda. This event is believed to be the largest earthquake ever recorded in South Sudan, and is one of the largest events known in all of Africa.

May 24 foreshock

At 19:34:44 on May 24, 1990, another large earthquake struck southern South Sudan. It occurred at a depth of with a of 6.1, of 6.5-6.8 and () of 6.5-6.6. The focal mechanism solution varies, with some showing the earthquake being the result of normal dip-slip faulting, while others suggesting it was the result of reverse dip-slip faulting instead.

May 24 mainshock

At 20:00:08, only a little over 25 minutes after the foreshock, an even stronger earthquake struck the region: the second strongest of the whole sequence. This event was a 6.6, 7.0, 7.1 quake that occurred at a depth of . The focal mechanisms by various sources again disagree, with some showing normal faulting, with others showing strike slip faulting. It caused additional structural damage to buildings previously affected by the first and strongest shock, however, no casualties occurred. The worst damage was observed in uninhabited areas.

July 9 mainshock

After the sequence had largely finished, another large shock struck the area for a final time. The last big earthquake in the sequence was a 6.0, 6.4-6.5 and 6.6 event. It occurred at a depth of . Focal mechanism solutions are split, with a roughly equal proportion of agencies and studies preferring a strike-slip event, with another equal proportion believing it to be a normal faulting event.

Damage

The mainshock killed 31 people and damaged buildings in Juba and Moyo, Uganda. Shaking was felt as far as

Nakuru Nakuru is a city in the Great Rift Valley, Kenya, Rift Valley region of Kenya. It is the capital of Nakuru County, and was formerly the capital of Rift Valley Province. As of 2019, Nakuru had an urban and rural population of 570,674 inhabitant ...

Kenya ) , national_anthem = "Ee Mungu Nguvu Yetu"() , image_map = , map_caption = , image_map2 = , capital = Nairobi , coordinates = , largest_city = Nairobi , ...

. The mainshock of May 24 did further damage. Government buildings and private instutions were damaged in

Terekeka Terekeka is a community in Central Equatoria, South Sudan. It is the headquarters of Terekeka County. Older buildings in Juba reported cracked walls. Between 8,000 and 10,000 of the displaced required extra relief and shelter. 300,000 people were made homeless across the region as a result of the earthquakes.

References

Sources * * * * *

External links

M 7.2 - 69 km ENE of Juba, South Sudan
–

United States Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...

M 6.5 - 54 km NNE of Juba, South Sudan
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M 7.1 - 63 km NNE of Juba, South Sudan
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M 6.6 - 60 km N of Juba, South Sudan
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* * * * {{Earthquakes in Africa South Sudan earthquakes South Sudan earthquakes South Sudan earthquakes South Sudan earthquakes Earthquakes in Africa South Sudan earthquakes