The Foumban Shear Zone, or Central Cameroon Shear Zone (CCSZ), is a fault zone in Cameroon

Cameroon

Cameroon, officially the Republic of Cameroon , is a country in west Central Africa. It is bordered by Nigeria to the west; Chad to the northeast; the Central African Republic to the east; and Equatorial Guinea, Gabon, and the Republic of the Congo to the south. Cameroon's coastline lies on the...

 that has been identified with the Pernambuco fault

Pernambuco Fault

The Pernambuco fault or Pernambuco Shear Zone in northeastern Brazil is a splay fault radiating from the Transbrasiliano lineament eastwards to the coast, a major geological feature....

 in northeastern Brazil

Brazil

Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...

, which splays from the Trans-Brazilian Lineament.
It is part of the Central African Shear Zone

Central African Shear Zone

The Central African Shear Zone is a wrench fault system extending in an ENE direction from the Gulf of Guinea through Cameroon into Sudan.The structure is not well understood....

 (CASZ) and dates to at least 640 million years ago.
The zone was rejuvenated several times, usually with a dextral movement, before and during the opening of the South Atlantic in the Cretaceous

Cretaceous

The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 period.

The Foumban shear zone is a series of faults associated with major mylonite

Mylonite

Mylonite is a fine-grained, compact rock produced by dynamic recrystallization of the constituent minerals resulting in a reduction of the grain size of the rock. It is classified as a metamorphic rock...

 zones, a segment of the CASZ.
The CASZ can be traced from the Sudan

Sudan

Sudan , officially the Republic of the Sudan , is a country in North Africa, sometimes considered part of the Middle East politically. It is bordered by Egypt to the north, the Red Sea to the northeast, Eritrea and Ethiopia to the east, South Sudan to the south, the Central African Republic to the...

 to the Adamawa plateau

Adamawa Plateau

The Adamawa Plateau is a plateau region in west-central Africa stretching from south-eastern Nigeria through north-central Cameroon to the Central African Republic. The plateau was named after Fulani Muslim leader Modibo Adama. The part of the plateau that lies in Nigeria is more popularly known...

, after which its path is obscured by volcanoes. Based on reconstruction of the configuration of South America before it separated from Africa, the zone can be identified with the Pernambuco fault.
The shear zone underlies a chain of extinct volcanoes, called the Cameroon Volcanic Line.
In August 1986 a magnitude 5 earthquake with epicenter near Lake Nyos

Lake Nyos

Lake Nyos is a crater lake in the Northwest Region of Cameroon, located about northwest of Yaoundé. Nyos is a deep lake high on the flank of an inactive volcano in the Oku volcanic plain along the Cameroon line of volcanic activity...

indicated that the shear zone may be again reactivating.