Some of the geological challenges and opportunities associated with the dynamics of the Cenozoic East African Rift System

The Cenozoic East African Rift System (EARS) is the largest continental rift valley system on Earth. Extending over a total distance of approximately 4,500 km, and with an average width of about 50 km, it is home to some of East Africa's largest urban populations and some of its most important transport, energy and water supply infrastructure. Rifting commenced during the Early Miocene and crustal extension has continued to the present day, posing seismic and volcanic hazards throughout its history of human occupation. Deep-seated landslides also present significant challenges for public safety, land management and infrastructure development on the flanks of rift margins. The rift floor itself poses a range of geohazards to community livelihood and engineering infrastructure, including ground fissuring and cavity collapse, flooding and sedimentation. On the positive side, the development of the EARS has created hydrocarbon and geothermal energy resources, and geomaterials for use as aggregates and cement substitutes in road and building construction. Optimising the use of these resources requires careful planning to ensure sustainability, while land use management and infrastructure development must take full consideration of the hazards posed by the ground and the fragility and dynamism of the human and physical environment.

The first Miocene fossils from coastal woodlands in the southern East African Rift

The Miocene is a key time in the evolution of African mammals and their ecosystems witnessing the origin of the African apes and the isolation of eastern coastal forests through an expanding biogeographic arid corridor. Until recently, however, Miocene sites from the southeastern regions of the continent were unknown. Here we report discovery of the first Miocene fossil teeth from the shoulders of the Urema Rift in Gorongosa National Park, Mozambique, at the southern East African Rift System. We provide the first 1) radiometric age determinations of the fossiliferous Mazamba Formation, 2) reconstructions of past vegetation in the region based on pedogenic carbonates and fossil wood, and 3) description of fossil teeth from the southern rift. Gorongosa is unique in the East African Rift System in combining marine invertebrates, marine vertebrates, terrestrial mammals, and fossil woods in coastal paleoenvironments. The Gorongosa fossil sites offer the first evidence of persistent woodlands and forests on the coastal margins of southeastern Africa during the Miocene, and an exceptional assemblage of fossil vertebrates including new species. Further work will allow the testing of hypotheses positing the formation of a northeast-southwest arid corridor isolating species on the eastern coastal forests from those elsewhere in Africa.

Volcanic activity and hazard in the East African Rift Zone

Over the past two decades, multidisciplinary studies have unearthed a rich history of volcanic activity and unrest in the densely-populated East African Rift System, providing new insights into the influence of rift dynamics on magmatism, the characteristics of the volcanic plumbing systems and the foundation for hazard assessments. The raised awareness of volcanic hazards is driving a shift from crisis response to reducing disaster risks, but a lack of institutional and human capacity in sub-Saharan Africa means baseline data are sparse and mitigating geohazards remains challenging.

Improving depth estimations of African earthquakes using teleseismic data, and influence for the East-African rift seismic hazard characterization

SUMMARY Well-constrained earthquake depth estimations are important for seismic hazard determination. As local networks of the East-African Rift are usually too sparse for reliable depth estimations, we used detections of pP and sP phase arrivals (the so-called depth phases) at teleseismic distance to constrain earthquake depths in this region. We rely on a fully automatic Cepstral analysis approach, first validated at the global scale using the ISC-EHB catalogue, then applied on the East-African seismicity. We investigated 9575 earthquakes from magnitude 2 since 2005 which allows us to constrain the depth estimation of 584 events with magnitude mainly above 3.5, complemented by 139 reliable depth estimations from previous studies based on teleseismic data as well. To ensure a final catalogue as complete as possible, we also identified from regional catalogues 113 earthquakes assumed to be well constrained, based on network geometry empirical criteria. Thanks to this study, we finally propose new earthquake depth distributions for the seismic source zonation defined by Poggi et al., in order to estimate the seismic hazard of the East African Rift region. Including those new distributions in the source models leads to significant changes of seismic hazard assessments results.