Tanzania

Tanzania is one of the most seismically active countries in Africa, uniquely straddling both branches of the East African Rift System. The western rift branch extends southward through Lake Tanganyika and Lake Rukwa along Tanzania's western border with Burundi, DRC, and Zambia, while the eastern rift branch — associated with the Eyasi and Manyara rifts — cuts across northern Tanzania south of the Serengeti. Both branches terminate in Tanzania, making the country a pivot point for understanding the geometry and mechanics of the East African Rift.

Lake Tanganyika, shared between Tanzania, DRC, Burundi, and Zambia, is bounded by active normal [[fault]]s that have produced several large historical earthquakes. The Tanganyika basin is the world's second deepest lake (1,470 m), and the faults that created this deep graben are seismically active. A significant earthquake sequence struck the northern end of Lake Tanganyika near Kigoma in 1914, causing damage along the lake shores. More recently, a magnitude 6.8 earthquake struck beneath Lake Tanganyika in December 2005, causing felt shaking across western Tanzania, eastern DRC, Burundi, and Rwanda. Several people were injured and buildings damaged in Kigoma.

The Lake Rukwa Rift, which extends northeast-southwest between Lakes Tanganyika and Malawi, produced the most powerful earthquake in Tanzania's modern instrumental record. On 13 December 1910, a magnitude 7.4 earthquake struck near Lake Rukwa in the Mbeya region, generating a surface rupture and causing massive landslides that altered the course of the Lwewero River. This event is among the largest historical intraplate earthquakes in East Africa. A more recent magnitude 5.9 event struck the Mbeya region in February 2017, injuring several people.

The eastern branch of the rift in northern Tanzania is expressed through the Eyasi-Manyara-Natron trough system. This zone is associated with the world-famous Oldoinyo Lengai volcano in the Gregory Rift, which is the only active carbonatite volcano on Earth. Oldoinyo Lengai has erupted multiple times in the 20th and 21st centuries, producing both explosive events and prolonged lava effusion from its carbonatite lava lake. Each eruptive phase is accompanied by [[seismic-wave]] swarms that reflect the ascent of carbonatite magma through the volcanic plumbing.

The Kilimanjaro region, where Africa's highest peak (5,895 m) rises above the Amboseli Plain, is also seismically active. Kilimanjaro itself is a potentially active stratovolcano, and occasional low-magnitude earthquake swarms have been recorded in the region. The North Tanzania Divergence — the area where the eastern rift bifurcates around the Kilimanjaro-Ngorongoro volcanic highlands — represents one of the most complex tectonic geometries in the African rift system, and the [[epicenter]]s in this area show mixed fault mechanisms reflecting the diverging rift geometry.

The largest damaging earthquake to affect Dar es Salaam, Tanzania's economic capital, occurred in 1919 when an offshore Indian Ocean earthquake (estimated magnitude 7.0) generated a small [[tsunami]] that caused damage along the coast. More recently, the 2016 Kagera earthquake (magnitude 5.7 near the Rwanda-Tanzania border) killed 17 people in northwestern Tanzania and injured hundreds, demolishing or damaging numerous buildings.

[[seismic-wave]] propagation in Tanzania is strongly influenced by the contrasting lithospheric properties of the two rift branches and the cratonic blocks between them. The Tanzania craton, an ancient Archean nucleus that lies between the eastern and western rift branches, transmits seismic energy efficiently with low attenuation. The younger rift lithosphere transmits energy less efficiently due to higher temperatures and partial melting in the upper mantle. The [[aftershock]] sequences following significant Tanzanian earthquakes are typically well-developed, often extending for several months after major events. The [[magnitude]] distribution of instrumentally recorded events in Tanzania shows continuous activity in the magnitude 2 to 4 range along the rift axes, with periodic magnitude 5 to 7 events on major border faults.