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On 26th May 2021, an earthquake with a moment magnitude Mw 5.1 hit the densely populated cities of Gisenyi (Rwanda) and Goma (D.R. Congo) which sit on the active East African Rift System. It was one of the largest earthquakes associated with the 2021 Mount Nyiragongo eruption. Although of moderate magnitude, the earthquake substantially damaged manmade structures. This paper presents field observations on the geotechnical impact, building damage, and factors contributing to the heightened destruction caused by this moderate earthquake. The damage pattern observed in the field indicates that masonry structures with inadequate seismic detailing were the most damaged buildings. In addition, the statistical analysis of the damaged buildings indicates most of the damaged structures were located in plains covered by volcanic soil. The intensity of the waves was estimated using the building damage data based on the European Macroseismic Scale (EMS-98). An intensity distribution map was generated for the surveyed area, suggesting EMS-98 intensity of VIII or IX along the eastern basin boundary fault and VII around the cities of Goma and Gisenyi where the land is composed of black cotton soil of volcanic origin. The higher intensity values along the eastern basin-bounding fault indicate that a reevaluation of the seismic hazard for the region is necessary. Since this is the first-ever such damage survey for the region, the developed intensity map can be used to understand the correlation between the intensity of the ground motion and damage severity which contributed to the seismic hazard assessment of the study area. [ABSTRACT FROM AUTHOR]

Sedimentary provenance analysis has rarely been applied to continental rifts, because source-rock terrains are assumed to be uniform and supply systems stable and closely connected to the formation of graben shoulders. Here, we test the suitability of multi-proxy sedimentary provenance analysis to unravel the evolution of a segment of the East African Rift System from its sedimentary record, where an extreme relief has been created and a continent-wide drainage system has been affected. Multi-proxy techniques include petrographic-mineralogical analysis (framework, heavy mineral spectra, zircon morphology, and colour), as well as single-grain garnet geochemistry, Zr-in-rutile thermometry, and geochronological methods (detrital zircon U–Pb ages). Published data are compiled and complemented by new U–Pb detrital zircon data of rift sediments. Because a comprehensive database of basement source-rock compositions from East Africa is missing, published modern river sand compositions have been added to provide endmember source fingerprints. The selected Albertine Rift is surrounded by four main source terrains within the East African Basement, which cannot be separated clearly by individual provenance indicators. Most useful were heavy mineral spectra, garnet composition, and with limitation Zr-in-rutile thermometry showing different metamorphic overprint. U–Pb detrital zircon spectra assisted well in detecting juvenile magmatism of different orogenic events, but repeated inheritance in younger units prevented a strict allocation. Petrographic maturity turned out to be more dependent on multi-cycle detritus as on climate shift. Applying endmember composition to rift sediments, three evolutionary stages of the Albertine Rift could be identified which coincide with basin-scale unconformities. Moreover, we could prove a large, southwest trending drainage network in East Africa during the Miocene, which was destructed step-wise by ongoing rifting. Extreme uplift of the Rwenzori Mountains up to 5109 m could be documented by a specific set of provenance indicators justified by modern river sand. Three main lessons can be drawn from this study: (1) basement units can be only reliably characterized by a combination of provenance-sensitive parameters, and here, the frequently used U–Pb detrital zircon ages are not sufficient; (2) it is possible to define subunits, e.g., individual fault-blocks within the rift; and (3) chemical weathering is unproblematic when applying a multi-parameter approach even in a tropical setting. [ABSTRACT FROM AUTHOR]

The East African Rift System (EARS) provides an ideal natural laboratory for studying the mechanisms of tectonic plate breakup and continental drift, as well as a unique perspective for exploring the maturation process of continental rifting and its drivers. This study combines high-resolution satellite gravity data and seismic tomography model with an integrated geophysical approach to reveal the density structures in the upper mantle of the EARS. The results show that the northeastern to central Congo and Zimbabwe Craton exhibit significant high-density anomalies extending up to 250 km, which is indicative of a thicker and more intact lithosphere. In contrast, the Uganda, Tanzania, eastern and southern Congo, and Kaapvaal Craton show shallow high-density anomalies underlain by low-density anomalies that are clearly derived from the deeper mantle, indicating a thining of the lithosphere with some degree of possible melting at the base. The various rift segments of the EARS exhibit different rift morphologies. The Main Ethiopian Rift and the Kenya Rift of the Eastern Rift Branch show strong low-density anomalies, indicating intense melting, which is much stronger than that observed in the Western Rift Branch. However, the two rifts may have originated from the same mantle uplift in which the low-density anomalies of the Eastern and Western Rift Branches connected in the deep upper mantle. The lower portion of the Malawi Rift exhibits weaker low-denstiy anomalies, which can be observed to the south of the Malawi Rift, extending further south as a continuation of the EARS. Combining the results of previous kinetics simulations and our density perturbation results, it can be inferred that the Eastern Rift Branch is mainly affected by active rifting, while the Western Rift Branch is affected by both active and passive rifting. [ABSTRACT FROM AUTHOR]

The distribution and timing of Neogene extensional structures along the offshore Tanzania margin and their influence on submarine sediment dispersal pathways remain poorly constrained. This knowledge gap limits understanding of the propagation of the East African Rift System (EARS) in the western Indian Ocean. In this study, we use 2D and 3D seismic reflection data to explore a portion of the upper slope region offshore the Rufiji River delta which led to the discovery of a new extensional structure. Horizon maps and seismic sections extracted from the 3D volume reveal that the slope was intersected by W‐E‐oriented turbidite channels during the Cenozoic until the early Pliocene (5.3 Ma). Since then, the opening of this graben, whose timing is also constrained by stratigraphic horizon flattening, has led to a southward reorientation of these channels, a pattern that persists today, as evidenced by the flow direction of the channels at the modern seafloor. 2D seismic profiles reaching depths of 10 s two‐way travel time (TWT) indicate that the formation of this graben is not related to the reactivation of Mesozoic structures. In detail, seismic data show that the acoustic basement is intersected by extensional faults, likely related to the Jurassic rift tectonics, which is reactivated during the middle Cretaceous forming a gentle monocline. The lack of deformation in the post‐Cretaceous suggests a period of tectonic quiescence which persists until the establishment of a new extensional regime responsible for the graben's opening, indicating a decoupling between Mesozoic and Neogene tectonics. Considering the similarity in kinematics, orientation and timing between the graben and other structures along the margin, onshore and offshore, we interpret this graben to be generated by a later tectonic phase of the EARS. These new results may indicate that tectonic stresses associated with the EARS migrated from the Tanzania craton, where the oldest rift structures are dated to ca. 25 Ma, to the western Indian Ocean, where the tectonic activity started during the middle‐late Miocene to Pliocene. [ABSTRACT FROM AUTHOR]

The East African Rift System (EARS) is the youngest rift with the eastern and western branches, consisting of multiple secondary rifts. It is generally characterized by low extent of exploration and great exploration potential. Identifying the differences in hydrocarbon accumulation conditions in various rifts is very important in providing guidance for hydrocarbon exploration and selecting favorable exploration targets in this area. Based on the interpretation of first-hand seismic-geological data, and combining other materials such as commercial databases and open access literature, the structural characteristics of the main rifts in the eastern and western branches of the EARS are comparatively analyzed; based on the anatomy of the discovered hydrocarbon reservoirs, the rifts of the EARS are classified into four types depending on their structural styles, including double-fault type, simple single-fault type, single-fault transfer type, and single-fault terrace type, and the control of structural style over hydrocarbon accumulation in the EARS is discussed. In the Western Branch of the EARS, large rifts such as the Albertine Rift and the Tanganyika Rift are mainly of double-fault type and single-fault transfer type, and only some small rifts are of the simple single-fault type. The rifts in the Eastern Branch of the EARS are generally small; the rifts in the northern section of the Western Branch are mainly of the simple single-fault type, and those in the southern section are mainly of the single-fault terrace type. The hydrocarbon potential of double-fault rifts is the greatest, followed by that of simple single-fault rifts and single-fault transfer rifts, and the hydrocarbon potential of single-fault terrace rifts is relatively limited. The results obtained from a comparative analysis of the structures, sediment fills, and reservoir elements of various rifts show that the west side of the Albertine Rift, the southeast of the Tanganyika Rift, the Kerio Rift, and the land in the northwest of the Turkana Rift have great exploration potential. [ABSTRACT FROM AUTHOR]

The southern East African Rift System (EARS) is an early-stage continental rift with a deep seismogenic zone. It is associated with a low-to-moderate seismic hazard, but due to its short and sparse instrumental record, there is a lack of ground-motion studies in the region. Instead, seismic hazard assessments have commonly relied on a combination of active crustal and stable continental ground-motion models (GMMs) from other regions without accounting for the unusual geological setting of this region and evaluating their suitability. Here, we use a newly compiled southern EARS ground-motion database to compare six active crustal GMMs and four stable continental GMMs. We find that the active crustal GMMs tend to underestimate the ground-motion intensities observed, while the stable continental GMMs overestimate them. This is particularly pronounced in the high-frequency intensity measures (>5 Hz). We also use the referenced empirical approach and develop a new region-specific GMM for southern EARS. Both the ranked GMMs and our new GMM result in large residual variabilities, highlighting the need for local geotechnical information to better constrain site conditions. [ABSTRACT FROM AUTHOR]

The Malawi Rift is localized within Precambrian amphibolite‐granulite facies metamorphic belts, bounded by up to 150 km long border faults, and generates earthquakes throughout ∼40 km thick crust. Rift‐related faults are inferred to exploit pre‐existing weaknesses that allow rifting of otherwise dry and strong crust. It is unclear what these weaknesses are, and how localization into weak zones can be reconciled with strength required for lower crustal seismicity. We present results of mineral equilibria modeling, which indicate that Proterozoic metamorphism generated dry crust dominated by a quartz‐feldspar assemblage that is metastable at current conditions. For rift propagation to be possible at current cool thermal gradients and in mechanically strong, dry quartzofeldspathic rocks, mid‐ to lower‐crustal strain must be localized into relatively weak, inherited shear zones that deform primarily by aseismic, viscous creep. These shear zones are embedded within high‐strength crust, and interaction between creeping shear zones and enveloped or surrounding rocks may locally increase stress and trigger frictional, seismic slip at mid‐ to lower‐crustal depths. Over time, this interaction may produce a fracture network that allows infiltration of fluids. We therefore suggest that during rifting of previously deformed and metamorphosed crust, major faults are most likely to grow from below, with their location and orientation prescribed by underlying inherited viscous shear zones. In this case, fluids may infiltrate and locally weaken metastable lower crust, including allowing time‐dependent fluid‐driven seismicity and local partial melting, but length‐scales of this weakening is limited by the scale of the permeability network. Plain Language Summary: In Malawi, East Africa, the Earth's crust is slowly splitting apart. This "rifting" has two unusual characteristics: (a) the crust is thick and strong and therefore difficult to split apart, and (b) there are earthquakes at greater depth and temperature than typical for the continents. We propose that the reason rifting occurs with these two characteristics, in this location, is that the crust is inherited from past periods of mountain building. Based on thermodynamic principles, specifically what minerals are stable under what conditions, we model the composition of Malawi crust in the geological past. We then compare those results to current conditions. We find that the likely inherited composition of Malawi crust is unstable under current conditions, but needs an addition of water to undergo reactions to new, stable minerals. We also note that deformation is only possible in weak zones inherited from past deformation, and these zones will deform by high‐temperature flow of rock, not generating earthquakes. However, flow of local weak zones may induce fracturing in surrounding harder rocks, generating local earthquakes and a fracture system that water can flow along. Over time, this water infiltration can weaken the crust and ultimately allow continental rifting as seen further north in Africa. Key Points: The Malawi crust is mostly dry, metastable and frictionally strong, and rifting requires viscous flow in inherited lower crustal shear zonesMajor faults are likely to grow from below, with their location and orientation prescribed by underlying inherited viscous shear zonesViscous flow in heterogeneous crust may trigger lower crustal seismicity generating permeability that allows infiltration of external fluids [ABSTRACT FROM AUTHOR]

The East African Rift System (EARS) provides an ideal natural laboratory for studying the mechanisms of tectonic plate breakup and continental drift, as well as a unique perspective for exploring the maturation process of continental rifting and its drivers. This study combines high-resolution satellite gravity data and seismic tomography model with an integrated geophysical approach to reveal the density structures in the upper mantle of the EARS. The results show that the northeastern to central Congo and Zimbabwe Craton exhibit significant high-density anomalies extending up to 250 km, which is indicative of a thicker and more intact lithosphere. In contrast, the Uganda, Tanzania, eastern and southern Congo, and Kaapvaal Craton show shallow high-density anomalies underlain by low-density anomalies that are clearly derived from the deeper mantle, indicating a thining of the lithosphere with some degree of possible melting at the base. The various rift segments of the EARS exhibit different rift morphologies. The Main Ethiopian Rift and the Kenya Rift of the Eastern Rift Branch show strong low-density anomalies, indicating intense melting, which is much stronger than that observed in the Western Rift Branch. However, the two rifts may have originated from the same mantle uplift in which the low-density anomalies of the Eastern and Western Rift Branches connected in the deep upper mantle. The lower portion of the Malawi Rift exhibits weaker low-denstiy anomalies, which can be observed to the south of the Malawi Rift, extending further south as a continuation of the EARS. Combining the results of previous kinetics simulations and our density perturbation results, it can be inferred that the Eastern Rift Branch is mainly affected by active rifting, while the Western Rift Branch is affected by both active and passive rifting.

Abstract Background The initial phase of earthquake hazard assessment involves the consolidation of diverse magnitude scales, thereby requiring the homogenization of various magnitudes. Moment magnitude (Mw) emerges as the preferred descriptor for a range of magnitudes, encompassing local magnitude (ML), teleseismic magnitude (e.g., mb and MS), duration magnitudes (MD), and other magnitude proxies. Unlike alternative scales, Mw does not exhibit saturation at high magnitudes, enhancing its reliability. To achieve uniformity in magnitude representation, diverse regression techniques are employed, with the General Orthogonal Regression (GOR) method being widely regarded as the most dependable, accounting for uncertainty in both independent and dependent variables. Methods This study utilized the International Seismological Centre (ISC) Catalogue ( http://www.isc.ac.uk/ ) to compile an array of events related to the East Africa Rift System (EARS). Subsequently, the General Orthogonal Regression method was applied to merge and harmonize the collected data. Furthermore, the research computed Gutenberg-Richter b-values using the newly unified magnitude. Results Notably, the conversion relationships between magnitude proxies, including MS-mb, mb-Mw, MS-Mw, and ML-Mw, exhibited robust correlations, with coefficients of 0.86, 0.80, 0.88, and 0.94, respectively. In contrast, the relationship between ML and mb proxies revealed a notably weaker correlation, registering a coefficient of 0.54. Ultimately, the study identified a magnitude of completeness and a b-value of 3.8 and 0.71, respectively, for the EARS region, providing valuable insights for earthquake hazard assessment in this area. Conclusion Generally, the homogeneous catalogue is a step forward in seismicity assessment and geodynamic activities in the EARS. Hence, developing the empirical equations for the area is essential for future studies on seismic hazards and engineering applications due to the peculiarity of EARS’s geological and tectonic characteristics.

Abstract The Malawi Rift is localized within Precambrian amphibolite‐granulite facies metamorphic belts, bounded by up to 150 km long border faults, and generates earthquakes throughout ∼40 km thick crust. Rift‐related faults are inferred to exploit pre‐existing weaknesses that allow rifting of otherwise dry and strong crust. It is unclear what these weaknesses are, and how localization into weak zones can be reconciled with strength required for lower crustal seismicity. We present results of mineral equilibria modeling, which indicate that Proterozoic metamorphism generated dry crust dominated by a quartz‐feldspar assemblage that is metastable at current conditions. For rift propagation to be possible at current cool thermal gradients and in mechanically strong, dry quartzofeldspathic rocks, mid‐ to lower‐crustal strain must be localized into relatively weak, inherited shear zones that deform primarily by aseismic, viscous creep. These shear zones are embedded within high‐strength crust, and interaction between creeping shear zones and enveloped or surrounding rocks may locally increase stress and trigger frictional, seismic slip at mid‐ to lower‐crustal depths. Over time, this interaction may produce a fracture network that allows infiltration of fluids. We therefore suggest that during rifting of previously deformed and metamorphosed crust, major faults are most likely to grow from below, with their location and orientation prescribed by underlying inherited viscous shear zones. In this case, fluids may infiltrate and locally weaken metastable lower crust, including allowing time‐dependent fluid‐driven seismicity and local partial melting, but length‐scales of this weakening is limited by the scale of the permeability network.

The Southwestern Branch of the East African Rift System propagates through the Central and Southern African plateaus and ends in the Okavango Makgadikgadi Zambezi Basin. This basin hosts the Okavango Graben and the Eiseb Graben, considered as the terminus of the Southwestern Branch of the rift. To the southeast, the Makgadikgadi Basin is affected by a series of normal faults forming the Makgadikgadi Rift Zone (MRZ) which regional geodynamic significance remains unclear. Based on fieldwork and geomorphic analysis, we revisited the geomorphological features associated with paleolakes and the fault pattern within the Makgadikgadi Basin to better constrain the dynamics of the MRZ. Fault scarps and offsets along linear dunes show normal‐dip kinematics of faults, indicating a NW‐SE extension direction in the area. Furthermore, lacustrine shorelines in the basin are undeformed, proving that they post‐date the fault activity. The previously published ages of these shorelines demonstrate that the MRZ currently has a low tectonic activity. Integrated in the geodynamic framework of the region, these results suggest that present‐day deformation shifts toward the Okavango Graben north of the MRZ. We therefore propose a "zip‐opening" model to explain the propagation of the Southwestern Branch of the East African Rift System where the tip of the system progressively progresses southwestward, driven by motions of the continental plates. Key Points: Geomorphic indicators better constrain kinematics and deformation relative chronology of the Makgadikgadi Rift Zone (MRZ), BotswanaLow activity of the MRZ suggests that present‐day rift activity shifts from the Mid‐Zambezi Rift to the Okavango GrabenWe propose a NE‐SW propagation model of the East African Rift System at its southwestern terminus driven by plates relative motions [ABSTRACT FROM AUTHOR]

The presence of pre‐existing fabrics at all lithospheric scales has been proven to be of primary importance in controlling the evolution of continental rifts. Indeed, observations from natural examples show that even in conditions of orthogonal rifting, when extension should result in simple fault patterns dominated by normal faults orthogonal to extension vectors, inherited fabrics induce complex arrangements of differently‐oriented extension‐related structures. This paper explored the influence of inherited fabrics on rift‐related structures by using a series of analog models deformed in a centrifuge. The models reproduced a brittle‐ductile crustal system and considered the presence of pre‐existing discrete fabrics in the brittle crust in conditions of orthogonal narrow rifting. These fabrics were reproduced by cutting the brittle layer at different orientations with respect to the extension direction. Modeling shows pre‐existing fabrics have a significant influence on rift‐related faults, provided that the angle between inherited fabrics and the rift trend is less than 45°. In these conditions, fabrics cause prominent segmentation of rift‐related faults and induce the development of isolated depocenters. Pre‐existing fabrics strongly influence the geometry of extension‐related structures, resulting in curved fault patterns and en‐echelon arrangement of oblique faults. These findings provide insights into the development of continental rift systems in nature: our modeling shows indeed significant similarities (i.e., peculiar fault architecture and geometries) with the faults in different sectors of the East African Rift System (e.g., the Magadi and Bogoria basin, Kenya Rift), testifying that reactivation of inherited fabrics is a paramount process in shaping continental rifts. Key Points: Centrifuge analog models show that inherited fabrics strongly influence rift structures when their angle to the rift trend is <45°Inherited fabrics affect the top‐view geometry of rifts, leading to curvature and segmentation of faults as well as isolated depocentersOur models display strong similarities with different examples in the East African Rift System, well explaining the fault pattern evolution [ABSTRACT FROM AUTHOR]

Background: The initial phase of earthquake hazard assessment involves the consolidation of diverse magnitude scales, thereby requiring the homogenization of various magnitudes. Moment magnitude (Mw) emerges as the preferred descriptor for a range of magnitudes, encompassing local magnitude (ML), teleseismic magnitude (e.g., mb and MS), duration magnitudes (MD), and other magnitude proxies. Unlike alternative scales, Mw does not exhibit saturation at high magnitudes, enhancing its reliability. To achieve uniformity in magnitude representation, diverse regression techniques are employed, with the General Orthogonal Regression (GOR) method being widely regarded as the most dependable, accounting for uncertainty in both independent and dependent variables. Methods: This study utilized the International Seismological Centre (ISC) Catalogue (http://www.isc.ac.uk/) to compile an array of events related to the East Africa Rift System (EARS). Subsequently, the General Orthogonal Regression method was applied to merge and harmonize the collected data. Furthermore, the research computed Gutenberg-Richter b-values using the newly unified magnitude. Results: Notably, the conversion relationships between magnitude proxies, including MS-mb, mb-Mw, MS-Mw, and ML-Mw, exhibited robust correlations, with coefficients of 0.86, 0.80, 0.88, and 0.94, respectively. In contrast, the relationship between ML and mb proxies revealed a notably weaker correlation, registering a coefficient of 0.54. Ultimately, the study identified a magnitude of completeness and a b-value of 3.8 and 0.71, respectively, for the EARS region, providing valuable insights for earthquake hazard assessment in this area. Conclusion: Generally, the homogeneous catalogue is a step forward in seismicity assessment and geodynamic activities in the EARS. Hence, developing the empirical equations for the area is essential for future studies on seismic hazards and engineering applications due to the peculiarity of EARS's geological and tectonic characteristics. Article highlights: The empirical relations developed on the basis of the updated catalogue for the EARS are crucial and strong agreement with global studies for the earthquake hazard analysis in the region. The magnitude of completeness, Mc, for the EARS is significantly low as catalogues are continuously being updated. b-value obtained reveals that the EARS is experiencing active stress field with b-value significantly lower than 1. [ABSTRACT FROM AUTHOR]

Ethiopia's Cenozoic flood basalt magmatism, uplift, and rifting have been attributed to one or more mantle plumes. The Nubian plate, however, has drifted 500–1,000 km north since initial magmatism at ∼45 Ma, having developed above mantle that now underlies the northern Tanzania craton and the low‐lying Turkana Depression. Unfortunately, our knowledge of mantle wavespeed structure and mantle transition zone (MTZ) topography below these regions is poorest, due to a historical lack of seismograph stations. The same data gap means we lack constraints on lithospheric structure in and around the NW–SE trending Mesozoic Anza rift. We exploit data from new seismograph networks in the Turkana Depression and neighboring northern Uganda to develop AFRP22, a new African absolute P‐wavespeed tomographic model that resolves whole mantle structure along the entire East African rift system. We also map MTZ thickness using Ps receiver functions. East Africa's thinnest MTZ (∼25 km thinning) underlies the northwest Turkana Depression. AFRP22 reveals a co‐located, previously unrecognized, slow wavespeed plume tail, extending from the MTZ, deep into the lower mantle. This plume may thus have contributed, along with the African Superplume, to the development of the 45–30 Ma flood basalt province that preceded extension. Pervasive sub‐lithospheric slow wavespeeds imply that Turkana's present‐day low elevation is explained best by Mesozoic and Cenozoic‐age crustal thinning. At ∼100 km depth, AFRP22 illuminates a fast wavespeed SE Ethiopian plateau. In addition to governing the northernmost limit of Mesozoic Anza rifting, the refractory nature of this lithospheric block likely minimized Cenozoic flood basalt magmatism there. Plain Language Summary: The Ethiopia‐Yemen plateau is capped by Earth's youngest continental flood basalt province. Its development, and that of the East African Rift that bisects it, has been linked to the presence of one or more mantle plumes. However, the African plate has moved 500–1,000 km north since the initial flood basalt phase at ∼45 Ma, meaning the mantle that underlies it is now overlain by northernmost Uganda and the low‐lying Turkana Depression. The Depression separates the Ethiopia‐Yemen and East African plateaus and was once the site of failed NE–SW rifting in Mesozoic time (S. Sudan and Anza rifts). Here, we use two complementary techniques to image the mantle beneath East Africa using new recordings of distant earthquakes collected in the Turkana Depression and northernmost Uganda alongside existing data from across Africa. Combined, these methods help illuminate where hot mantle rock has risen to the surface within mantle plumes and resulted in magmatism. Intriguingly, East Africa's hottest mantle today, at transition zone depths, underlay the Ethiopian flood basalt province at 30 Ma. At shallower depths, a fast seismic wavespeed zone in SE Ethiopia, which was unaffected by flood basaltic magmatism, likely controlled the location of earlier episodes of failed Anza rifting. Key Points: New seismic data from the Turkana Depression enhances images of East African mantle wavespeed and discontinuity structureThinnest transition zone in East Africa is below the NW Turkana Depression and is underlain by a mid to lower mantle plume tailRefractory lithosphere in SE Ethiopia governed northern extent of Mesozoic Anza rifting and southeastern limit of flood basaltic magmatism [ABSTRACT FROM AUTHOR]

The southern East African rift system (EARS) is geologically rare considering its early-stage continental rift setting combined with a deep seismogenic zone. Several seismically vulnerable communities are located within this tectonically active region, resulting in a significant seismic risk. However, the ground motion and seismic hazard analyzes necessary to increase the earthquake preparedness in the region have been limited due to the relatively short instrumentation history and scarce ground motion data available. Here, we present a newly compiled ground motion database for the southern EARS which is critically lacking and preventing local ground motion studies. This database includes a regional catalog of 882 earthquakes spanning 1994–2022 (magnitudes 3–6.5) with available waveform records within epicentral distances of 300 km. Three different velocity models were used to relocate 256, 255, and 252 events, respectively, to quantify depth sensitivity, relocating events down to depths of 35–40 km. The final database contains 10,725 time-series records from 353 stations along with P- and S-wave phase arrivals for each record. The ground motion database contains peak ground acceleration and velocity and 5% damped pseudo-spectral acceleration for 291 frequencies from 1.0 to 30 Hz for the horizontal components. In addition, a Fourier amplitude spectrum table for 212 frequencies from 0.1 to 30 Hz is included. The database is accessible through the ISC repository (https://doi.org/10.31905/4GGVBFBE). [ABSTRACT FROM AUTHOR]

Magmatic intrusion and faulting both accommodate crustal extension in magma‐rich rifts. However, quantitative constraints on the contribution of faulting to total extension and along‐rift variations of faulting during the final stages of break‐up are lacking. We targeted the Danakil Depression (Afar, Ethiopia) to conduct a quantitative, high‐resolution study of fault activity and interaction in a magma‐rich rift near break‐up. Quantitative analysis of >500 rift axis faults, identified using remote sensing data (satellite imagery, DEMs), shows an increase in fault density, length and connectivity away from magmatic segments. Kinematic and earthquake focal mechanism data demonstrate a transition from transtensional opening in the northern and central sub‐regions of the rift to oblique opening in the southern Giulietti Plain and Tat‐Ali sub‐regions. Oblique opening is attributed to the along‐axis step between the Erta‐Ale and Harak sub‐regions. Integration of seismic reflection and borehole data with the mapped faults shows that extension is primarily accommodated by magmatism within the rift center, with faulting more significant toward the ends of the rift. ∼30% of crustal extension is accommodated by axial faulting in areas of low magmatism, highlighting the importance of faulting even in the final stages of magma‐rich rifting. Comparing our findings with spreading ridge morphology and structure, relevant due to the rift maturity and extensive magmatism, we conclude that the Danakil Depression is in a transitional stage between continental rifting and seafloor spreading. Spatial changes in the importance of faulting and magmatism in accommodating extension, alongside rift morphology, resemble the relationships observed along spreading ridges. Key Points: Switch from transtensional to oblique opening along the rift correlates to lateral steps of rift segmentsAt least 30% of extension in magma‐poor areas of the depression is accommodated by upper crustal axial faultingCharacteristics and spatial distribution of axial faulting in the Danakil Depression mimics that observed along seafloor spreading ridges [ABSTRACT FROM AUTHOR]

Abstract Ethiopia's Cenozoic flood basalt magmatism, uplift, and rifting have been attributed to one or more mantle plumes. The Nubian plate, however, has drifted 500–1,000 km north since initial magmatism at ∼45 Ma, having developed above mantle that now underlies the northern Tanzania craton and the low‐lying Turkana Depression. Unfortunately, our knowledge of mantle wavespeed structure and mantle transition zone (MTZ) topography below these regions is poorest, due to a historical lack of seismograph stations. The same data gap means we lack constraints on lithospheric structure in and around the NW–SE trending Mesozoic Anza rift. We exploit data from new seismograph networks in the Turkana Depression and neighboring northern Uganda to develop AFRP22, a new African absolute P‐wavespeed tomographic model that resolves whole mantle structure along the entire East African rift system. We also map MTZ thickness using Ps receiver functions. East Africa's thinnest MTZ (∼25 km thinning) underlies the northwest Turkana Depression. AFRP22 reveals a co‐located, previously unrecognized, slow wavespeed plume tail, extending from the MTZ, deep into the lower mantle. This plume may thus have contributed, along with the African Superplume, to the development of the 45–30 Ma flood basalt province that preceded extension. Pervasive sub‐lithospheric slow wavespeeds imply that Turkana's present‐day low elevation is explained best by Mesozoic and Cenozoic‐age crustal thinning. At ∼100 km depth, AFRP22 illuminates a fast wavespeed SE Ethiopian plateau. In addition to governing the northernmost limit of Mesozoic Anza rifting, the refractory nature of this lithospheric block likely minimized Cenozoic flood basalt magmatism there.

Understanding the crustal structure and the storage and movement of fluids beneath a volcano is necessary for characterizing volcanic hazard, geothermal prospects and potential mineral resources. This study uses local earthquake traveltime tomography to image the seismic velocity structure beneath Nabro, an off‐rift volcano located within the central part of the Danakil microplate near the Ethiopia‐Eritrea border. Nabro underwent its first historically documented eruption in June 2011, thereby providing an opportunity to analyze its post‐eruptive state by mapping subsurface fluid distributions. We use a catalog of earthquakes detected on a temporary seismic array using machine learning methods to simultaneously relocate the seismicity and invert for the three‐dimensional P‐ and S‐wave velocity structures (VP, VS) and the ratio between them (VP/VS). Overall, our model shows higher than average P‐ and S‐wave velocities, suggesting the presence of high‐strength, solidified intrusive magmatic rocks in the crust. We identify an aseismic region of low VP, low VS, and high VP/VS ratio at depths of 6–10 km b.s.l., interpreted as the primary melt storage region that fed the 2011 eruption. Above this is a zone of high VS, low VP, and low VP/VS ratio, representing an intrusive complex of fractured rocks partially saturated with over‐pressurized gases. Our observations identify the persistence of magma in the subsurface following the eruption, and track the degassing of this melt through the crust to the surface. The presence of volatiles and high temperatures within the shallow crust indicate that Nabro is a viable candidate for geothermal exploration. Plain Language Summary: Understanding the structure of the crust and the distribution and movement of fluids beneath a volcano allows for the assessment of volcanic hazard, geothermal potential and possible mineral extraction. To identify different regions of the crust and differentiate between fluids, we use the fact that the speed of seismic waves depends on the material they are traveling through. For example, seismic waves will travel through magma (molten, or liquid, rock) at lower speeds than in the surrounding rock. The focus of this study is Nabro volcano in Eritrea, which erupted in 2011. We use earthquakes that have been automatically detected following the eruption to image the structure of the crust in the form of 3D variations in seismic wave speeds. This identifies a volume of magma stored at depths of 6–10 km below sea level, which fed the eruption. Above this, we observe a region of rocks that are likely remnants of earlier eruptions at Nabro, with fractures containing gases at high pressure. The source of this high pressure is the release of gas from the magma storage zone. The presence of hot fluids means Nabro could be used as a source of geothermal power in the future. Key Points: 3D seismic modeling reveals the structure of the magmatic and hydrothermal systems beneath Nabro volcano in EritreaThe primary melt storage region feeding the 2011 eruption is located at depths of 6–10 km below sea levelDegassing from the magma storage zone causes overpressure in partially saturated, fractured intrusive complex above [ABSTRACT FROM AUTHOR]

The Rungwe Volcanic Province (RVP) in the East African Rift System, SW Tanzania, provides a unique opportunity to investigate geothermal resources in the context of particularly complex continental rifting processes. To support geothermal resource targeting in the RVP, we present a revised neotectonic structural map based on an interpretation of aeromagnetic data constrained by 2D-forward modelling of magnetic anomalies integrated with the distribution of previously reported faults, seismic epicentre locations, 3D magnetotelluric resistivity models and surface geothermal manifestations. Magnetic anomalies in the RVP, including the nationally prominent Mbeya anomaly, are related to the high magnetic susceptibility or remanent magnetism of Precambrian rocks and Cretaceous carbonatite intrusions buried in the rift under a varying thickness of non-magnetic sediments and volcanic rocks. Magnetic lineaments are related to structures controlling the geometry of the Precambrian rocks and concealed dikes and the thickness of the sediments and volcanics. The recent Ngozi and Rungwe trachyte volcanics have relatively low magnetic susceptibility comparable to the low susceptibility of the sediments in the rift basins. The revised neotectonic structural map shows prominent NW, NE and NS-trending magnetic lineaments that correlate with previously reported faults and alignments of seismic epicentres in the study area and with the regional trend of the rift segments. The NE-trending magnetic lineaments are consistent with interpretations of the current stress field in the RVP. The main volcanoes in the RVP, Ngozi, Rungwe and Kiejo (also known as Kyejo and Kieyo), are aligned with the NW-trending linear magnetic feature joining the Lupa and Livingstone rift border faults. This lineament is intersected and frequently displaced by the NE and NS-trending lineaments, suggesting that the NE to NS-striking structures are younger. The Rungwe and Ngozi volcanoes as well as numerous "monogenetic" eruption centres and the Mwakaleli caldera, which originated ca. 2 Ma ago (Ebinger et al., 1989) following a large explosive eruption emplacing widespread ignimbrite deposits, are located within a zone of low-intermediate magnitude magnetic features forming a basin-like structure surrounded by magnetic high anomalies of the Precambrian basement structures. We interpret the intersections between the NW-trending intra-rift faults and the NS and NE-trending faults as favourable locations for wells to target high permeability within the geothermal resource conceptual models previously constructed using 3D MT resistivity imaging integrated with supporting geoscientific data. The intersections provide a focus area for follow-up ground mapping of subtle features that may be associated with very recent fault movement. [ABSTRACT FROM AUTHOR]

The East African Rift System (EARS) is a prime example of continental rifting, characterized by its iconic topographic features, which are significantly shaped by the interplay of tectonic and climatic forces. This review synthesizes past decades of morphotectonic studies (recent studies) on the plateau landscapes of the EARS, focusing particularly on their interiors and margins, and highlights their crucial role in advancing our understanding of landscape evolution. The paper revisits the legacy of geologic research in the EARS and delves into recent morphotectonic studies that quantify the rates and patterns of plateau incision, exhumation, and uplift through advanced thermochronological and topographic analyses. Additionally, the review identifies key unresolved questions, such as the origins of the plateau topography–whether from volcanic activity or mantle plume influence and explores how these plateaus maintained high elevations during the humid Oligocene Epoch without significant incision. The recent work described in this paper alongside legacy perspectives, continues to refine our geological understanding of the EARS, with broader implications for studies worldwide. • Introduces legacy views, and reviews recent studies of morphotectonics in the EARS. • A holistic approach to EARS, uncovering insights on rifting, volcanism, and landscape evolution. • Topo & thermochron unveil, cooling age, and incision rate, providing landscape insight. • Long-term incision rates reveal uplift; Cretaceous exhumation uncovered via thermochronology. [ABSTRACT FROM AUTHOR]

Geophysical methods are instrumental in characterizing lithospheric-scale heterogeneity beneath continental rifts and collisional zones. Seismic imaging techniques, in particular have played a significant role in imaging lithospheric discontinuities within the crust as well as its Moho boundary with the underlying sub-continental lithospheric mantle (SCLM). However, in geodynamic settings where there have been significant mafic magmatic underplating, the seismic Moho and the petrological Moho become distinct, making gravity methods more effective to image the compositional variation between the crust and the SCLM. Our work assesses one of the gravity modeling methods that can be applied to image the petrological Moho by introducing a new approach, which is referred to as the spectral analysis with piecewise regression (SAPR). To test the effectiveness of SAPR, we used the World Gravity Model 2012 (WGM 2012) to calculate the depth to the petrological Moho and the depth to the top of the Precambrian crystalline basement beneath the Lake Turkana rift within the East African Rift System in southern Ethiopia and northern Kenya. Subsequently, the results of the Moho depths from the SAPR were compared with previous Moho depth estimates using other gravity methods as well as controlled-source seismic techniques. [ABSTRACT FROM AUTHOR]

The Cenozoic East African Rift is a typical intracontinental rift at the germination stage of the Wilson cycle, which has long attracted the attention of geologists at home and overseas. The Albert Lake Depression is located at the northern most end of the west branch of the East African Rift System.It is an asymmetric (half) graben with a NW orientation. At present, good industrial oil and gas have been discovered in this area.The analysis of the subsidence evolution is of great significance to further reveal the tectonic subsidence characteristics and petroleum exploration potential of this depression.Based on drilling data, combined with seismic interpretation, and analysis of subsidence history, burial history and fault activities, this paper reclassifies tectonic units, and summarizes the characteristics of tectonic subsidence. The relationship between subsidence and fault activities, the law of subsidence center migration and its indicating significance for petroleum exploration were discussed in this study. The results show that the secondary structural units in the east of the Albert Lake Depression are mainly controlled by the eastern boundary faults, and the F1 and F2 faults play a major role in controlling the subsidence and formation of the eastern steep fault belt, the eastern fault terrace zone and the three structural adjustment belts. The subsidence rate of the southern sub sag was large in the early stage, which was conducive to the formation of extremely thick source rocks in Late Miocene.With the northward migration of the subsidence center, the Upper Miocene and Lower Pliocene source rocks were developed in the northern sub sag.The structural belt around the subsidence center is the favorable direction area for hydrocarbon migration and accumulation. This study provides a new basis for further petroleum in Albert Lake Depression of the East African Rift System.

The evolution of normal fault arrays during rift extension reflects paleo-plate boundary conditions and lithospheric rheology, while controlling seismic hazard and the distribution of basin-hosted resources. Yet, constraining their spatiotemporal development is challenging, particularly where geophysical and subsurface data are absent. Here, we test footwall exhumation modelling using thermochronology as a means of elucidating 4D normal fault array evolution, using the Miocene Central Basin of the Malawi Rift as a natural laboratory. Along-strike trends in exhumational cooling recorded by vertical transects of apatite fission-track and (U–Th)/He data from the basin-bounding Usisya fault scarp reveal a diachronous footwall uplift history that closely reflects 4D trends in hangingwall subsidence recorded by previously published seismic and well data. Initially, pronounced footwall exhumation is restricted to the centres of a series of four isolated normal faults, mirroring the distribution of early syn-rift depocentres. The later onset of footwall exhumation in the intervening areas marks subsequent fault segment propagation and linkage as they formed the through-going Usisya fault system. Elsewhere, cumulative exhumation recorded in the Usisya footwall remains low, coinciding with more significant intra-basinal faulting. This study shows that footwall exhumation modelling constrained by thermochronologic data can reveal the spatiotemporal evolution and strain partitioning within normal fault arrays. • Thermochronology transects along the Usisya fault scarp record footwall exhumation. • Usisya fault evolution is reflected in basin stratigraphy revealed by seismic data. • Malawi rift related cooling along Usisya commenced in the middle Miocene. • Footwall exhumation modelling reveals complex 4D fault exhumation and linkage. [ABSTRACT FROM AUTHOR]

In this study we map the entire East African Rift System (EARS) within a global surface‐wave velocity model to better constrain the structure of the underlying mantle, as well as patterns that might be associated with its continuation in the Mozambique Channel. We use all publicly available seismograms from the African continent, amounting to 1296 stations and more than 30 years of recordings. From these data, we obtain dispersion curves using both ambient noise and teleseismic earthquakes. To our measurements, we add global counterparts and jointly invert them for phase‐velocity maps. We exploit a linearized inversion based on the ray theory, with an adaptive parameterization that allows for maximizing the resolution of the final maps based on the density of data coverage. We thus image the main African cratons and also some of the Archean blocks within them. We highlight the discontinuous nature of magmatic activity along the EARS and also display low‐velocity anomalies beneath the Comores Archipelago, Madagascar and Bassas da India volcanic islands and seamounts. This last low‐velocity anomaly is in the direct continuation of the EARS and could unveil an important magmatic system in the Mozambique Channel. Plain Language Summary: The East African Rift System (EARS) is where tectonic plates are breaking and drifting apart in Africa. The opening of the EARS most probably finds its origin in the forces existing in the underlying mantle. The goal of this study is to better understand the structure of the inside of the Earth in the region. To do that, we use waves registered by seismometers to create maps of the crust and upper mantle (the lithosphere). These maps display where the waves travel at different speed, giving us information about the Earth's structure. In our maps of wave speed, we see several very interesting things. First, we see fast speeds in areas of thick lithosphere (cratons), and our resolution gives us some details on their inner structure. Then, we see three patches of slow speeds along the EARS, suggesting that this system is discontinuous, with some very active points where volcanic fields are present. Finally, we see slow speeds in the Mozambique Channel, where no such feature was reported before. This suggests that the lithosphere is hot there and perhaps contains some melt. This may show the development of the EARS southwards into the Mozambique Channel. Key Points: Joint inversion of global and regional phase‐velocity measurements using an adaptive parameterizationGlobal phase‐velocity maps characterized by an improved resolution throughout the East African Rift SystemLow‐velocity anomaly beneath Mozambique Channel probably ascribed to a significant magmatic system [ABSTRACT FROM AUTHOR]

Carbonatite occurrences are reported in Lueshe, Kirumba, Bingo and Mombadio in the Democratic Republic of Congo (DRC), within the western branch of the East African Rift System (EARS). These rocks intrude Precambrian rocks , which are mainly quartzites and mica schists. Lateritic profiles from Lueshe and Bingo are ore-bearing minerals enriched in Nb2O5 and phosphate minerals. The Lueshe and Bingo exploitable quantities are estimated to be 30 Mt at a grade of 1.34% Nb2O5 and 7 Mt at a grade of 2.86% Nb2O5, respectively. These carbonatites were explored and exploited by some mining companies in the 1970s and 2000s. They show geological and geochemical similarities to other exploitable carbonatites in the EARS, including Mrima Hill in Kenya, Panda Hill in Tanzania and the world-class Araxá and Catalão carbonatites in Brazil. The Lueshe and Kirumba alkaline massifs dates, determined using the whole-rock Rb–Sr method, are respectively 822 ± 120 and 803 ± 22 Ma and are intimately linked to the Rodinia Supercontinent breakup. These dates are analogous to other regional carbonatite dates like the Matongo carbonatite in Burundi. However, further geological, petrological and geochemical studies on carbonatite complexes are essential in DRC. Most importantly, the economic potentials of Kirumba and Mombadio should be evaluated. Simultaneously, the dates of the Bingo and Mombadio carbonatites are crucial for the elucidation of their geodynamic settings. [ABSTRACT FROM AUTHOR]

Single grain, laser-ablation inductively-coupled-plasma mass spectrometry (LA-ICP-MS) trace element analysis of volcanic glass shards has emerged as a valuable tool in constructing regional tephrostratigraphic frameworks for paleoanthropological sites. The limiting factors in analysing single shards for trace element compositions are a) analytical precision (% RSD), which is dependent on the size and homogeneity of the area available for analysis, and b) accuracy (% bias), which is dependent on compositional differences between natural rhyolitic samples and available reference materials. The limited vertical thickness of the tephra glasses, the small surface areas accessible for ablation and the presence of inclusions requires increased spatial resolution, ideally utilizing laser spot diameters ≤20 μm, to achieve effective 'fingerprinting' of tephra layers. Typically, LA-ICP-MS, 'spot' analyses at such high spatial resolution yield degraded precision (>10% RSDs) and accuracy (> ±5% bias) for natural tephra samples compared to reference materials. Here we present a novel approach for LA-ICP-MS trace element analysis of tephra glass and apply the method to two Plio-Pleistocene tephra layers, namely the Upper and Lower Nariokotome tuffs, and their enclosed pumice clasts, from the Turkana Basin, NW Kenya. These tuffs were chosen as they are characterised by homogeneous yet distinct major element glass composition and are examples of tephra layers of significant paleoanthropological importance. Our approach involves the use of ablation 'traverses' across individual glass fragments and we utilize the Lower Nariokotome Tuff, as a matrix-matched secondary reference material for our analytically 'unknown' samples. This method yields significant improvement in both analytical precision (1–5% RSD) and accuracy (<±5% bias) for 25 trace elements, using both 10 μm and 20 μm beam diameters. These results allow us to identify trace element discriminators for these tuffs and successfully correlate pumices to their respective eruption events. This study contributes to the developing field of single-grain LA-ICP-MS trace element geochemistry as a tephra correlation tool by enhancing the data quality acquired for natural samples. • Traverse ablation strategy in LA-ICP-MS trace element geochemistry improves precision. • Trace element geochemistry provides 'fingerprints' for tephra identification. • Improved precision enables identification of co-magmatic pumice and tephra layers. • Improved analytical approach for inter- and intra-basin tephrochronology. [ABSTRACT FROM AUTHOR]

• Elongated calderas were often considered proxy for the regional extension. • We run circular caldera collapse analogue models afterward elongated by extension. • We prove that extension justifies only 13% of elongation for calderas in the MER. • Only specific sectors of caldera faults are capable of reactivation under extension. • Caldera structures influence the architecture of newly forming regional faults. Caldera collapses are paramount volcano-tectonic features because they form during hazardous explosive volcanic eruptions, they are ideal sites for geothermal development and mineral resources exploitation, and also because they preserve the evidence of the interaction between caldera magmatism and the regional tectonic processes. Despite this, many aspects of the caldera collapse process remain unclear, particularly concerning the interaction between caldera and tectonic related fault systems. We therefore used analogue models 1) to quantify the effect of regional strain on caldera elongation in extensional settings, such as the Main Ethiopian and the Kenya rifts, 2) to describe the effect of regional strain on caldera structures and, vice-versa 3) to document, for the first time, "the other side of the coin", that is how caldera structures affect the formation of newly forming regional extensional faults. Our models showed that tectonic extension only explains a small proportion (e.g. 13% for the Main Ethiopian Rift) of the elongation of most rift calderas. Furthermore, we showed how specific segments of caldera faults may accommodate regional extension by reactivating, therefore precluding caldera elongation. Finally, we showed how the presence of caldera structures may influence the geometry of newly forming regional normal faults, that display a marked curvature, "faking" caldera ring faults. We have suggested that these "fake" curved caldera ring faults may lead to incorrect estimations of caldera elongation in nature. In addition, such faults may also mislead geothermal fluid exploration, as they are likely disconnected from the caldera structures or the caldera plumbing system, and less likely the locus of hydrothermal fluid flow. [Display omitted] [ABSTRACT FROM AUTHOR]

Little is known about rift kinematics and strain distribution during the earliest phase of extension due to the deep burial of the pre-rift and earliest rift structures beneath younger, rift-related deposits. Yet, this exact phase of basin development ultimately sets the stage for the location of continental plate divergence and breakup. Here, we investigate the structure and strain distribution in the multiphase Late Paleozoic-Cenozoic magma-poor Rukwa Rift, East Africa during the earliest phase of extension. We utilize aeromagnetic data that image the Precambrian Chisi Shear Zone (CSZ) and bounding terranes, and interpretations of 2-D seismic reflection data to show that, during the earliest rift phase (Permo-Triassic ‘Karoo’): 1) the rift was defined by the Lupa border fault, which exploited colinear basement terrane boundaries, and a prominent intra-basinal fault cluster (329° ± 9.6) that trends parallel to and whose location was controlled by the CSZ (326°); 2) extensional strain in the NW section of the rift was accommodated by both the intra-basinal fault cluster and the border fault, where the intra-basinal faulting account for up to 64% of extension; in the SE where the CSZ is absent, strain is primarily focused on the Lupa Fault. Here, the early-rift strain is thus, not accommodated only by the border fault as suggested by existing magma-poor early-rift models; instead, strain focuses relatively quickly on a large border fault and intra-basinal fault clusters that follow pre-existing intra-basement structures; 3) two styles of early-rift strain localization are evident, in which strain is localized onto a narrow discrete zone of basement weakness in the form of a large rift fault (Style-1 localization), and onto a broader discrete zone of basement weakness in the form of a fault cluster (Style-2 localization). We argue that the CSZ and adjacent terrane boundaries represent zones of mechanical weakness that controlled the first-order strain distribution and rift development during the earliest phase of extension. The established early-rift structure, modulated by structural inheritance, then persisted through the subsequent rift phases. The results of our study, in a juvenile and relatively well-exposed and data-rich rift, are applicable to understanding the structural evolution of deeper, buried ancient rifts.

Extant snake faunas have their origins in the mid-Cenozoic, when colubroids replaced booid-grade snakes as the dominant species. The timing of this faunal changeover in North America and Europe based on fossils is thought to have occurred in the early Neogene, after a period of global cooling opened environments and made them suitable for more active predators. However, new fossils from the late Oligocene of Tanzania have revealed an early colubroid-dominated fauna in Africa suggesting a different pattern of faunal turnover there. Additionally, molecular divergence times suggest colubroid diversification began sometime in the Paleogene, although the exact timing and driving forces behind the diversification are not clear. Here we present the first fossil snake referred to the African clade Lamprophiinae, and the oldest fossil known of Lamprophiidae. As such, this specimen provides the only potential fossil calibration point for the African snake radiation represented by Lamprophiidae, and is the oldest snake referred to Elapoidea. A molecular clock analysis using this and other previously reported fossils as calibration points reveals colubroid diversification minimally occurred in the earliest Paleogene, although a Cretaceous origin cannot be excluded. The elapoid and colubrid lineages diverged during the period of global warming near the Paleocene-Eocene boundary, with both clades diversifying beginning in the early Eocene (proximate to the Early Eocene Climate Optimum) and continuing into the cooler Miocene. The majority of subclades diverge well before the appearance of colubroid dominance in the fossil record. These results suggest an earlier diversification of colubroids than generally previously thought, with hypothesized origins of these clades in Asia and Africa where the fossil record is relatively poorly known. Further work in these regions may provide new insights into the timing of, and environmental influences contributing to, the rise of colubroid snakes. [ABSTRACT FROM AUTHOR]

Aim: The roles of geodynamics, climatic variability and landscape evolution in shaping aquatic biodiversity patterns on the African continent remain poorly understood. We studied the geographical origin and phylogenetic relationships of an Afrotropical freshwater snail genus to examine the role of drainage evolution on diversification and range evolution. The relevance of fish provinces in bio‐regionalization of invertebrates was explored, as well as the evolution of habitat specificity. Location: Africa including Madagascar. Taxon: Lanistes (Gastropoda: Ampullariidae). Methods: Based on a sampling covering the entire geographical range, we reconstructed a fossil‐calibrated multi‐locus molecular phylogeny using maximum likelihood and Bayesian inference approaches. After applying species delimitation methods, we estimated ancestral areas and habitats and examined rates of diversification through time using lineage through time plots. Results: RAxML and MrBayes analyses resulted in highly congruent topologies and a strongly supported phylogeny. Our BEAST analysis indicate that Lanistes probably originated in the Eocene about 50 Ma and the most recent common ancestor (MRCA) of all 23 Lanistes OTUs in our study may have inhabited an area including the Central African and adjacent Lower Guinean biogeographical regions. A steeper increase in species accumulation from the middle Miocene (c. 15 to 10 Ma), followed by a decrease towards the present was found. Sympatry and jump dispersal were the common cladogenetic events and only a single anagenetic dispersal event was detected. The biogeographical analyses further suggest that Madagascar was colonized from East Africa and that the Zambezi River was colonized at least twice independently. Seven species are confined to rivers and three live exclusively in lakes. The estimation of ancestral habitats suggested that the MRCA of all Lanistes probably evolved in a riverine habitat. Main conclusions: The diversification of Lanistes started in the Eocene and occurred at a constant pace apart from a possible climate‐related increase in the Miocene. This study highlights the significance of temporal geographical isolation of river systems and subsequent reconnection in clade diversification and of jump dispersal in range evolution. More comparative analyses across various taxa are needed to obtain a better understanding of African freshwater biodiversity. [ABSTRACT FROM AUTHOR]

Tectonically active regions are characterized by complex landscapes comprising soils with heterogeneous physicochemical properties. Spatial variability of nutrient sources enhances landscape biodiversity and creates heterogeneous habitats potentially attractive for animals and humans. In this study, we analyze the role of geological processes in the distributions of soil nutrients in the southern Kenya Rift, a key region in the interpretation of early human-landscape interactions. Our aim is to determine how spatial variations in rock chemistry, as well as topographic gradients and localized zones of rock fracturing from tectonic faulting determine the distributions of plant-available soil nutrients in soils. We hypothesize that present-day soil nutrient levels reflect the long-term chemical and geomorphological characteristics of the landscape and underlying parent material, and that regions with high nutrient availability occur along pathways correlating with locations of hominin fossil sites. Analyses of 91 topsoil samples from the main geological units show that Calcium (Ca) deficiencies predominately occur in shallow soils developed on trachytic volcanic rocks and granitic gneisses, while high Ca levels are associated with basaltic parent material and sedimentary deposits of mixed sources. XRF analysis of rock samples confirms that CaO levels in trachyte rocks are significantly lower than those in basalts, and Ca mobilization in basalt is more effective than in trachyte. Along two toposequences in densely faulted basaltic and trachytic rocks, we observed slope dependent soil nutritional gradients and a systematic increase of the concentrations of Ca, Mg and SOC in topsoils of colluvial sediments downslope of active normal faults. Known hominin sites in the region are located either along corridors of long-term Ca availability or at short-term nutrient hotspots potentially related to active CO2 degassing along active fault zones. This implies a strategic advantage of Ca-rich regions for hominin subsistence strategies, such as provision of predictable constraints on the distribution and mobility of grazing animals in complex tectonic landscapes. Our study implies that geological processes impact nutrient distributions in the southern Kenya Rift. Results of this study have further implications for understanding the role of soils in the interpretation of hominin-landscape interactions in the early stages of human evolution.

Abstract The East African Rift System (EARS) is composed of around 78 Holocene volcanoes, but relatively little is known about their past and present activity. This lack of information makes it difficult to understand their eruptive cycles, their roles in continental rifting and the threat they pose to the population. Although previous InSAR surveys (1990–2010) showed sign of unrest, the information about the dynamics of the magmatic systems remained limited by low temporal resolution and gaps in the data set. The Sentinel‐1 SAR mission provides open‐access acquisitions every 12 days in Africa and has the potential to produce long‐duration time series for studying volcanic ground deformation at regional scale. Here, we use Sentinel‐1 data to provide InSAR time series along the EARS for the period 2015–2020. We detect 18 ground deformation signals on 14 volcanoes, of which six are located in Afar, six in the Main Ethiopian Rift, and two in the Kenya‐Tanzanian Rift. We detected new episodes of uplift at Tullu Moje (2016) and Suswa (mid‐2018), and enigmatic long‐lived subsidence signals at Gada Ale and Kone. Subsidence signals are related to a variety of mechanisms including the posteruptive evolution of magma reservoirs (e.g., Alu‐Dallafila), the compaction of lava flows (e.g., Nabro), and pore‐pressure changes related to geothermal or hydrothermal activity (e.g., Olkaria). Our results show that ∼20% of the Holocene volcanoes in the EARS deformed during this 5‐years snapshot and demonstrate the diversity of processes occurring.

On April 3, 2017, an earthquake of magnitude Mw 6.5 ruptured in Botswana in a region where there was no significant recent tectonic activity and where present-day deformation is believed to be negligible. The event was followed by several aftershocks distributed along NW-SE direction with NE-SW extension direction. We focused on the determination of reliable source parameters for the Mw 6.5 main shock using moment tensor inversion, in both time and frequency domains from regional, broadband waveform data. We retrieve the source depth at 38.4 km, probably the deepest earthquake observed in continental Africa. The estimated hypocentral depth of this earthquake is roughly about the Moho depth beneath the region, reflecting a deep source that is relatively rare in stable continental regions. The result may suggest that the seismogenic depth is as deep as the average global Moho thickness indicating the upper mantle and lower crust region is actively deforming due to a reactivation of the preexisting fault oriented in the NW-SE direction. The resulting focal mechanism of the event shows normal faulting with NE-SW extension direction. The result may provide useful information for contemporary geodynamic investigation of the area. [ABSTRACT FROM AUTHOR]

The East African Rift System (EARS) is composed of around 78 Holocene volcanoes, but relatively little is known about their past and present activity. This lack of information makes it difficult to understand their eruptive cycles, their roles in continental rifting and the threat they pose to the population. Although previous InSAR surveys (1990–2010) showed sign of unrest, the information about the dynamics of the magmatic systems remained limited by low temporal resolution and gaps in the data set. The Sentinel‐1 SAR mission provides open‐access acquisitions every 12 days in Africa and has the potential to produce long‐duration time series for studying volcanic ground deformation at regional scale. Here, we use Sentinel‐1 data to provide InSAR time series along the EARS for the period 2015–2020. We detect 18 ground deformation signals on 14 volcanoes, of which six are located in Afar, six in the Main Ethiopian Rift, and two in the Kenya‐Tanzanian Rift. We detected new episodes of uplift at Tullu Moje (2016) and Suswa (mid‐2018), and enigmatic long‐lived subsidence signals at Gada Ale and Kone. Subsidence signals are related to a variety of mechanisms including the posteruptive evolution of magma reservoirs (e.g., Alu‐Dallafila), the compaction of lava flows (e.g., Nabro), and pore‐pressure changes related to geothermal or hydrothermal activity (e.g., Olkaria). Our results show that ∼20% of the Holocene volcanoes in the EARS deformed during this 5‐years snapshot and demonstrate the diversity of processes occurring. Key Points: InSAR survey (2015–2020) detects deformation at 14 Holocene volcanoes in the East African Rift SystemEpisodes of uplift are detected on several centers with no historical eruptions (Corbetti, Suswa)New subsidence signals are caused by lava compaction at Kone and geothermal activity at Olkaria [ABSTRACT FROM AUTHOR]

The East African Rift System (EARS) exerted a major influence on river drainage basins and regional climate of east Africa during the Cenozoic. Recent studies have highlighted an offshore branch of the EARS in the western Indian Ocean, where the Kerimbas Graben and the Davie Ridge represent its sea floor expression. To date, a clear picture of the impact and timing of this EARS offshore branch on the continental margin of the western Indian Ocean, and associated sediment dispersal pathways, is still missing. This study presents new evidence for four giant canyons along the northern portion of the Davie Ridge offshore Tanzania. Seismic and multibeam bathymetric data highlight that the southernmost three canyons are now inactive, supra‐elevated relative to the adjacent sea floor of the Kerimbas Graben and disconnected from the modern slope systems offshore the Rovuma and Rufiji River deltas. Regional correlation of dated seismic horizons, integrated with well data and sediment samples, proves that the tectonic activity driving the uplift of the Davie Ridge in this area has started during the middle‐upper Miocene and is still ongoing, as suggested by the presence of fault escarpments at the sea floor and by the location and magnitude of recent earthquakes. Our findings contribute to placing the Kerimbas Graben and the Davie Ridge offshore Tanzania in the regional geodynamic context of the western Indian Ocean and show how the tectonics of the offshore branch of the EARS modified the physiography of the margin, re‐routing the deep‐water drainage network since the middle Miocene. Future studies are needed to understand the influence of changing sea floor topography on the western Indian Ocean circulation and to evaluate the potential of the EARS offshore tectonics in generating tsunamigenic events. [ABSTRACT FROM AUTHOR]

• Mapping of geothermal systems by remote sensing aeromagnetic data, satellite remote sensing data and geological mapping. • The geothermal potential of the East African Rift System (EARS). • Agreement between results from different sources (geological structures, LST anomalies, indicator mineral alterations, geothermal surface manifestations, and geology) suggests potential geothermal system(s). The Lake Natron region is one of the potential geothermal resource areas in Tanzania, this is based on previous studies that focused on geology and the characteristics of the hot springs found in this region. However, the exact locations and sizes of the geothermal system(s)in this region are still unknown and require further exploration. This study used aeromagnetic data, Digital Elevation Model (DEM) data, multispectral remote sensing Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data that is characterized with spatial resolution of up to 15 m and extended wavelength range to Shortwave Infrared Region (SWIR) of the electromagnetic spectrum, to identify potential areas for geothermal systems. The datasets were processed to produce geological structures, indicator mineral alterations for geothermal areas and land surface temperature (LST) anomalies, which were used as proxies to the geothermal systems. Remote sensing data were processed using various techniques to improve the signals from geological features of interest. In the processing of ASTER data, the processing techniques included band ratios, false composite images, and supervised classification. Field observation was conducted to verify the results along with geological mapping and identification of geological features around geothermal manifestations. Aeromagnetic and SRTM data analysis allowed to interpret surface and subsurface structures, and compare them with the field observations. Results have revealed that the main structural trend is NE-SW, which agrees with the field evidence. This trend reflects the regional tectonic framework and the influence of major faults. Field mapping realized the presence of geothermal manifestations such as hot springs with temperatures range between 32℃ and 51℃, and pH range between 8 and 11. All hot springs are located along the mapped structures and major faults of the East African Rift System. Some parts of the study area are characterized by LST anomalies and indicator mineral alterations such as clays, sulfates, carbonates and ferric iron, these are characteristic geothermal manifestations in geothermal systems. Overall observation has also revealed a good match between remote sensing mapped mineral alterations, LST anomalies and other geothermal surface manifestations, this includes also geothermal favorable structure settings such as bend in normal faults, displacement transfer zones and horse tail structures. Despite the prominent results from this study, there is still a need for detailed investigation using high spectral and spatial resolution remote sensing data, time series thermal infrared (TIR) data, the best fit LST inversion method, along with other geological information (e.g. MT/TM geophysical surveys and geochemistry) to further validate the identified geothermal system. [ABSTRACT FROM AUTHOR]

During the past 25 ka, southern Ethiopia has undergone tremendous climatic changes, from dry and relatively cold during the Last Glacial Maximum (LGM, 25–18 ka) to the African Humid Period (AHP, 15–5 ka), and back to present-day dry conditions. As a contribution to better understand the effects of climate change on vegetation and lakes, we here present a new Predictive Vegetation Model that is linked with a Lake Balance Model and available vegetation-proxy records from southern Ethiopia including a new phytolith record from the Chew Bahir basin. We constructed a detailed paleo-landcover map of southern Ethiopia during the LGM, AHP (with and without influence of the Congo Air Boundary) and the modern-day potential natural landcover. Compared to today, we observe a 15–20% reduction in moisture availability during the LGM with widespread open landscapes and only few remaining forest refugia. We identify 25–40% increased moisture availability during the AHP with prevailing forests in the mid-altitudes and indications that modern anthropogenic landcover change has affected the water balance. In comparison with existing archaeological records, we find that human occupations tend to correspond with open landscapes during the late Pleistocene and Holocene in southern Ethiopia.

Attenuation of seismic waves in the crust and the upper mantle has been studied in three global rift systems: the Baikal rift system (Eurasia), the North Tanzanian divergence zone (Africa) and the Basin and Range Province (North America). Using the records of direct and coda waves of regional earthquakes, the single scattering theory [Aki, Chouet, 1975], the hybrid model from [Zeng, 1991] and the approach described in [Wennerberg, 1993], we estimated the seismic quality factor (QC), frequency parameter (n), attenuation coefficient (δ), and total attenuation (QT). In addition, we evaluated the contributions of two components into total attenuation: intrinsic attenuation (Qi), and scattering attenuation (Qsc). Values of QC are strongly dependent on the frequency within the range of 0.2–16 Hz, as well as on the length of the coda processing window. The observed increase of QC with larger lengths of the coda processing window can be interpreted as a decrease in attenuation with increasing depth. Having compared the depth variations in the attenuation coefficient (δ) and the frequency (n) with the velocity structures of the studied regions, we conclude that seismic wave attenuation changes at the velocity boundaries in the medium. Moreover, the comparison results show that the estimated variations in the attenuation parameters with increasing depth are considerably dependent on utilized velocity models of the medium. Lateral variations in attenuation of seismic waves correlate with the geological and geophysical characteristics of the regions, and attenuation is primarily dependent on the regional seismic activity and regional heat flow. The geological inhomogeneities of the medium and the age of crust consolidation are secondary factors. Our estimations of intrinsic attenuation (Qi) and scattering attenuation (Qsc) show that in all the three studied regions, intrinsic attenuation is the major contributor to total attenuation. Our study shows that the characteristics of seismic wave attenuation in the three different rift systems are consistent with each other, and this may suggest that the lithosphere in the zones of these different rift systems has been modified to similar levels.