Coastal Louisiana is sinking, amplifying flooding and land loss, yet the seasonal component of this motion remains difficult to attribute. Satellite geodetic records from Baton Rouge spanning 2004-2024 reveal long-term subsidence of -2.69 +/- 0.69 mm/yr, with a superimposed annual oscillation of 10-15 mm that is in phase with river stage and confined-aquifer hydraulic head. This positive correlation is diagnostic of poroelastic deformation rather than surface loading. A poroelastic model of a semi-confined aquifer driven by hydraulic-head variations reproduces both the long-term and seasonal signals. The seasonal amplitude decreases logarithmically with distance from the intersection of the Baton Rouge Fault and the Mississippi River, as expected for radial pressure diffusion from a flux source. Fault-river intersections therefore act as seasonal conduits into deep aquifers, representing an underappreciated control on coastal land motion that is likely to strengthen as hydrological extremes intensify.

Rifts that initiate in mechanically strong, stable continental lithosphere are characterized by M > 5 earthquakes at depths >35 km near or below the crust mantle interface. Current models for deep rift zone earthquakes invoke elevated pore pressures associated with magmatism, and rapid stressing from magma intrusions. We evaluate the role of static stress changes caused by lateral density contrasts (magma intrusions) in the upper mantle and crust-mantle interface on mantle earthquakes. We use numerical models of static stress changes, and test models against seismic data from the Tanganyika rift, East Africa which has upper mantle earthquakes and locally elevated crustal Vp/Vs. The earthquake source mechanisms from these ML2.4-2.8 earthquakes show steep nodal planes and little correlation to crustal source mechanisms and E-W extension direction. Likewise, the direction of fast splitting from seismic anisotropy studies is oblique to predictions from earthquake source mechanisms. The models of density contrasts (magma intrusions) explored in this study predict differential stresses of 1-10 MPa, stresses consistent with average earthquake stress drops. The local stress field rotations around the edges of intrusive bodies can explain the variable source mechanisms and match the local rotation of shear wave splitting direction, providing a plausible mechanism for mantle earthquakes in cratonic rifts. By analogy, exhumed mantle from rift zones reveals pseudotachylites near intrusions. Metasomatic reactions in contact aureoles broaden density contrasts and reduce upper mantle strength, potentially enabling extension of initially cold, strong continental lithosphere.

Theory and geoscientific observations demonstrate that plate stretching, heating, faulting, active and frozen magma intrusions, and extrusive eruptive products are consequences of mantle upwelling mechanism driving continental rifting. Problematic to this picture is the lack of consensus on how, when and where these processes modify the crust’s thermal and mechanical structure. We use data from East Africa’s 300-km wide Turkana Depression to investigate how the superposition of these rift processes and the spatial migration of the active plate boundary through time within one geodynamic setting modify the crust’s structure. Utilizing ambient noise seismic methods and data from the 34 station Turkana Rift Arrays Investigating Lithospheric Structure (TRAILS) seismic network, we invert for Rayleigh and Love tomographic models and overlay results with our local earthquakes crustal splitting results. Preliminary results show that regions that experienced Eocene flood magmatism have localized high Vs of > 3.4 km/s at mid-lower crustal depths implying that flood magmatism is fed by unknown localized centers and/or dike swarms. Quaternary eruptive centers with Vs < 3.4 km/s at mid-lower crustal depths are punctuated and irregularly spaced suggesting that bottom-up mantle upwelling influence their location. Regions with superposed Cretaceous-Paleogene and Miocene-Recent rift phases have persistent low velocities (Vs ≥ 3.8 km/s) to the mid-crust with thinner crust (~ 20 km); the active Miocene-Recent rift structures are oblique to the largely inactive Cretaceous-Paleogene rift structures implying no reactivation of pre-existing structures during modern-day rifting.

The spatiotemporal characteristics of infrequent back‐arc rifting events and their relationships to volcanic unrest as well as other transient processes within the subduction system are not well known. We report 10 spatio‐temporal swarms of earthquakes that occurred along ∼175 km of the northern and central Taupō Volcanic Zone (TVZ) March–September 2019. The swarms lack clear mainshock‐aftershock distributions, suggesting involvement of pressurized fluids. The most energetic swarms occurred beneath the southwestern flank of Whakaari/White Island volcano (WI) and were accompanied by elevated SO 2 emissions and ∼8 mm southwest displacement of the edifice. Focal mechanisms of the WI swarms suggest horizontal dilation in the direction of tectonic extension achieved by slip along networks of closely spaced, NE‐striking normal faults linked by oblique‐slip to strike‐slip faults. Given the small GNSS displacements and upward‐migrating swarms, we favor the interpretation that magmatic volatiles were released along faults in response to changes in crustal stress. Based on the punctuated, cascading nature of swarms along the northern TVZ, we hypothesize that faults and magmatic systems are fluid‐rich, experiencing aseismic creep, and critically stressed, raising the possibility that small changes in crustal stress from slow slip along the Hikurangi subduction zone caused a reduction in the minimum horizontal stress. This change occurred along the entire northern TVZ over ∼5 months, potentially contributing to widespread volcanic unrest. The probable release of magmatic fluids from shallow magma bodies in the vicinity of WI between May and June argues against a causal relation to the 9 December 2019 WI eruption.

Large fluid volume injections into the subsurface are increasingly common across a range of industrial and remediation activities. However, deep fluid injections are often associated with increased seismicity within a few hundred kilometers of the injection sites. The role of aseismic slip as an important precursory signal in induced-seismicity has gained importance in the community due to two reasons: (a) the time and length scales of injection-induced earthquakes are inconsistent with realistic diffusivities, and fluid-transport models do not match observations, and (b) modern theories of fault weakening suggest that at very high fluid pressures, faults can experience aseismic slip for prolonged periods before ultimately transitioning to unstable, seismic failure driven by static stress transfer. Our work investigates far-field microseism triggering in NE Texas and NW Louisiana within the Haynesville shale-gas field that has developed since 2008. It includes the 2012 Mw 4.8 Timpson, TX earthquake, which has been attributed to wastewater injection. Seismicity from a temporary array and national monitoring show an increase in the number and magnitude of earthquakes in the area, with regular ML3 events near the Texas-Louisiana border. InSAR data indicate uplift around some injection wells. We consider multiple injection wells and compute the spatial distribution of geodetic strain rates derived from GNSS velocities and compare them with seismic strain rates from new earthquake data. In the decade following the 2012 event, several microseisms across the Texas-Louisiana border have been recorded, suggesting that critically stressed faults in the vicinity are being triggered in part by static stress transfer, as well as newer injection wells. We compare fault orientations to current stress, consider Coulomb stress change from the Timpson event, and use fluid transport models to explain the seismicity and vertical land motion observed in the Haynesville Shale play area.

The East African Rift System (EARS) is an active continental rift zone that hosts a diverse range of processes that result in recent and ongoing crustal deformation. To analyze these processes, we used Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) to complement the sparse GNSS velocity field with high resolution measurements of line-of-sight (LOS) deformation between 2015 and 2022. A broad survey approach was employed to detect new signals within the central section of the EARS, and to establish a baseline for future studies focused on tectonic, volcanic, and/or hydrologic deformation and change spanning geodetic time scales. With this regional approach, we were able to resolve signals varying over time-spans of a few weeks to several years that have magnitudes greater than similar to 1 cm/yr. Our resulting deformation field shows a diverse range of signals related to the processes listed above as well as other unknown sources. This includes up to 8.5 cm/yr of groundwater-related subsidence in Nairobi, up to 70 cm of LOS displacement during the eruption of Nyiragongo in 2021, and steady uplift in the Manyara basin with a rate of 2.8 cm/yr. We update previously published InSAR measurements of Mount Suswa volcano, and the geothermal fields in Olkaria. We also show LOS change ranging between 2 and 5 mm/yr over a distances of approximately 200 km spanning the Kenya Rift with the greatest differential rates occurring south of Lake Turkana. More generally, our results highlight the ambiguity of relying solely on the sparse network of GNSS for studies such as those characterizing tectonic motion and rift opening. Such studies are likely missing many important signals and/or includes sites that are contaminated with signals unrelated to the target process.

The East African rift overlies one or more mantle upwellings and it traverses heterogeneous Archaean-Paleozoic lithosphere rifted in Mesozoic and Cenozoic time. We re-analyze XKS shear wave splitting at publicly available stations to evaluate models for rifting above mantle plumes. We use consistent criteria to compare and contrast both splitting direction and strength, infilling critical gaps with new data from the Turkana Depression and North Tanzania Divergence sectors of the East African rift system. Our results show large spatial variations in the amount of splitting (0.1–2.5 s) but consistent orientations of the fast axes within rift zones: they are predominantly sub-parallel to the orientation of Cenozoic rifts underlain by thinned lithosphere with and without surface magmatism. The amount of splitting increases with lithospheric thinning and magmatic modification. Nowhere are fast axes perpendicular to the rift, arguing against the development of extensional strain fabrics. Thick cratons are characterized by small amounts of splitting (≤0.5 s) with a variety of orientations that may characterize mantle plume flow. Splitting rotates to rift parallel and increases in strength over short distances into rift zones, implying a shallow depth range for the anisotropy in some places. The shallow source and correlation between splitting direction and the shape of upper mantle thin zones suggests that the combination of channel flow and oriented melt pockets contribute > 1 s to the observed splitting delays. Enhanced flow, metasomatism, and melt intrusion at the lithosphere-asthenosphere boundary suggest that fluid infiltration to the base of the lithosphere may facilitate rifting of cratonic lithosphere.

Rift initiation within cold, thick, strong lithosphere and the evolving linkage to form a contiguous plate boundary remains debated in part owing to the lack of time-space constraints on kinematics of basement-involved faults. Different rift sectors initiate diachronously and may eventually link to produce a jigsaw spatial pattern, as in the East African rift, and along the Atlantic Ocean margins. The space-time distribution of earthquakes illuminates the geometry and kinematics of fault zones within the crystalline crust, as well as areas with pressurized magma bodies. We use seismicity and Global Navigation System Satellites (GNSS) data from the Turkana Rift Array Investigating Lithospheric Structure (TRAILS) project in East Africa and a new digital compilation of faults and eruptive centres to evaluate models for the kinematic linkage of two initially separate rift sectors: the Main Ethiopian Rift (MER) and the Eastern rift (ER). The ca. 300 km wide zone of linkage includes failed basins and linkage zones; seismicity outlines active structures. Models of GNSS data indicate that the ca. 250 km-wide zone of seismically active en echelon basins north of the Turkana Depression is a zone, or block, of distributed strain with small counterclockwise rotation that serves to connect the Main Ethiopian and Eastern rifts. Its western boundary is poorly defined owing to data gaps in South Sudan. Strain across the northern and southern boundaries of this block, and an ca. 50 km-wide kink in the southern Turkana rift is accommodated by en echelon normal faults linked by short strike-slip faults in crystalline basement, and relay ramps at the surface. Short segments of obliquely oriented basement structures facilitate across-rift linkage of faults, but basement shear zones and Mesozoic rift faults are not actively straining. This configuration has existed for at least 2-5 My without the development of localized shear zones or transform faults, documenting the importance of distributed deformation in continental rift tectonics. Crustal-scale cross sections illustrate the geometry and kinematics of extensional fault systems and magma intrusions achieving extension across the active linkage zone between the Main Ethiopian and Eastern rifts through previously rifted lithosphere of the Turkana depression. Brown dashed line is an estimate of Moho depth from seismic studies.image

The Coast of Louisiana is affected by accelerating sea level rise compounded by land subsidence, leading to land loss. Vertical crustal motions in the region are caused by natural and anthropogenic processes that vary temporally and spatially across the Gulf of Mexico. We investigate the role of growth faulting contributions to subsidence in a case study of Baton Rouge, where two E-W striking, down-to-the-south normal faults, the Denham Springs and Baton Rouge faults, cut compacted Pleistocene strata, and where sediment compaction should be minimal. We used InSAR time series and LiDAR differencing data spanning 1999-2020 to quantify modern vertical and horizontal displacements. After calibration with GNSS data, both methods reveal similar spatial patterns in ground motion, with the faults delimiting areas with different absolute rates. On average the area north of the Baton Rouge fault is subsiding faster than the south, opposite to the long-term sense of fault slip. LiDAR mean vertical rates range between -5 to -11 mm/y and -2.4 to -7 mm/y. InSAR time-series mean rates in the LOS direction range between -10.9 to -13.6 mm/y and -8 to -10.6 mm/y, respectively, for the north and south areas. Subsidence in the northern area likely is controlled by groundwater level changes caused by pumping as indicated by groundwater extraction models. The southern area average is likely influenced by the injection of fluids. Our results suggest volumetric changes caused by fluid extraction and injection in regions separated by growth faults that are creeping to accommodate the spatial variations in subsidence. Coastal Louisiana is affected by the combination of sea level rise and ground surface sinking, or subsidence. The contribution of subsidence due to natural and human activities varies in time and space. We used airborne LiDAR and SAR satellite data to estimate rates and spatial variations of vertical and horizontal surface motions between 1999 and 2020 in the metropolitan area of Baton Rouge where two faults with surface topography cross the region in a pattern like tilted dominos. We found that the entire area is experiencing subsidence, but that the subsidence rate is faster in the northern fault block than in the southern block of the study area, this pattern is opposite to the long-term fault motion. The spatial pattern of the results from LiDAR and SAR data are similar and relate to groundwater pumping in areas of fast subsidence and wastewater injection zones in areas of slow subsidence. Our results should be considered for future urban planning and water management. LiDAR differencing (1999-2018) and SAR time series (2004-2020) show similar spatial variations. LiDAR documents horizontal changes Subsidence varies between zones separated by growth faults and correlates with groundwater level changes and fluid injection Creep along the Baton Rouge growth fault likely accommodates spatial variations in subsurface fluid levels

Whakaari/White Island has been the most active New Zealand volcano in the 21st century, producing small phreatic and phreatomagmatic eruptions, which are hard to predict. The most recent eruption occurred in 2019, tragically claiming the lives of 22 individuals and causing numerous injuries. We employed shear-wave splitting analyses to investigate variations in anisotropy between 2018 and 2020, during quiescence, unrest, and the eruption. We examined spatial and temporal variations in 3,499 shear-wave splitting and 2,656 Vp/Vs ratio measurements. Comparing shear-wave splitting parameters from similar earthquake paths across different times indicates that the observed temporal changes are unlikely to result from variations in earthquake paths through media with spatial variability. Instead, these changes may stem from variations in anisotropy over time, likely caused by changes in crack alignment due to stress or varying fluid content. The most active volcano in New Zealand, known as Whakaari/White Island, has recently experienced numerous minor eruptions, which are hard to predict. The most recent eruption occurred in 2019, tragically claiming the lives of 22 individuals and causing multiple injuries. This study examines the stress field and characteristics of cracks within various parts of the volcano, during the period between 2018 and 2020. We used a method called shear-wave splitting, which examines the alignment of cracks by measuring the speed of seismic waves in different orientations, and another method that measures the ratio of the speed of two different types of waves traveling through the medium (Vp/Vs). Our analysis revealed that both shear-wave splitting and Vp/Vs changed over time in response to the variations in magmatic activity. This suggests that crack alignment, content, or numbers change in response to the stresses induced by magmatic activity at various depths within the volcano over time. Background fast orientations were concentrated parallel to the crater wall at both measurement stations Seismic waves that follow similar paths to the stations result in different fast orientations pre- and post-eruption Vp/Vs ratio can provide valuable insights into the nature and evolution of seismic anisotropy in the Earth's interior

The Turkana Depression in Eastern Africa separates the elevated plateaus of East Africa to the south and Ethiopia-Yemen to the north. It remains unclear whether the Depression lacks dynamic mantle support, or if the entire East Africa region is dynamically supported and the Depression compensated isostatically by thinned crust. Also poorly understood is how Miocene-Recent extension has developed across the Depression, connecting spatially separated magmatic rift zones in Ethiopia and Kenya. Receiver function analysis is used to constrain Moho depth and bulk-crustal VP/VS ratio below new seismograph networks in the Depression, and on the northern Tanzania craton. Crustal thickness is ∼40 km below northern Uganda and 30–35 km below southern Ethiopia, but 20–30 km below most of the Depression, where mass-balance calculations reveal low elevations can be explained adequately by crustal thinning alone. Despite the fact that magmatism has occurred for 45 Ma across the Depression, more than 15 Ma before East African Rift (EAR) extension initiated, bulk crustal VP/VS across southern Ethiopia and the Turkana Depression (∼1.74) is similar to that observed in areas unaffected by Cenozoic rifting and magmatism. Evidence for voluminous lower crustal intrusions and/or melt, widespread below the Ethiopian rift and Ethiopian plateau to the north, is therefore lacking. These observations, when reviewed in light of high stretching factors (β≤2.11), suggest Cenozoic extension has been dominated until recently by faulting and plate stretching, rather than magma intrusion, which is likely an incipient process, operating directly below seismically-active Lake Turkana. Early-stage EAR basins to the west of Lake Turkana, with associated stretching factors of β≈2, formed in crust only moderately thinned during earlier rifting episodes. Conversely, ∼23 km-thick crust beneath the Kino Sogo Fault Belt (KSFB) has small offset faults and thin sedimentary strata, suggesting almost all of the observed stretching occurred in Mesozoic times. Despite the KSFB marking the shortest path between focused extensional zones to the north and south, seismicity and GPS data show that modern extension is localized below Lake Turkana to the west. Failed Mesozoic rift zones, now characterized by thinned crust and relatively refractory mantle lithosphere, are being circumnavigated, not exploited by EAR rifting.

Abstract The role of lithospheric heterogeneities, presence or absence of melt, local and regional stresses, and gravitational potential energy in strain localization in continental rifts remains debated. We use new seismic and geodetic data to identify the location and orientation of the modern Nubia‐Somalia plate boundary in the 300‐km‐wide zone between the southern Main Ethiopian Rift (MER) and Eastern Rift (ER) across the Mesozoic Anza rift in the Turkana Depression. This region exhibits lithospheric heterogeneity, 45 Ma‐Recent magmatism, and more than 1,500 m of base‐level elevation change, enabling the assessment of strain localization mechanisms. We relocate 1716 earthquakes using a new 1‐D velocity model. Using a new local magnitude scaling with station corrections, we find 1 ≤ ML ≤ 4.5, and a b‐value of 1.22 ± 0.06. We present 59 first motion and 3 full moment tensor inversions, and invert for opening directions. We use complementary geodetic displacement vectors and strain rates to describe the geodetic strain field. Our seismic and geodetic strain zones demonstrate that only a small part of the 300 km‐wide region is currently active; low elevation and high‐elevation regions are active, as are areas with and without Holocene magmatism. Variations in the active plate boundary's location, orientation and strain rate appear to correspond to lithospheric heterogeneities. In the MER‐ER linkage zone, a belt of seismically fast mantle lithosphere generally lacking Recent magmatism is coincident with diffuse crustal deformation, whereas seismically slow mantle lithosphere and Recent magmatism are characterized by localized crustal strain; lithospheric heterogeneity drives strain localization.

As dynamic processes in the Earth’s mantle stretch and thin large sectors of the African plate, broad plateaus interrupted by deep valleys and flanking mountains have formed at the Earth’s surface. These vertical and horizontal crustal movements occur concurrent with global climate changes, both of which happen over diverse spatial and temporal scales. Together, they modulated eastern Africa’s habitats for early hominins, and for flora and fauna in general. The habitat for hominin evolution, therefore, is shaped by bottom-up and top-down processes. Broad plateau uplift in Ethiopia had initiated by 30 Ma, coincident with or after flood magmatism at 45 Ma when dry seasonal woodland environments initiated in eastern Africa. The fossil-rich sedimentary sequences partially filling the 30–70-km-wide rift basins record the history of human evolution, as well as the complex interplay between climate change, uplift, volcanism, and faulting in equatorial Africa. The lake shorelines and hydrothermal systems served as oases for hunter-gatherers, and the rough topography of the faulted landscape may have served as refugia. Here, we outline the relevant time–space patterns to establish the geodynamic and paleoclimatic context for human evolution in eastern Africa.

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.

The Ethiopian-Yemen plateaus have been affected by plume-related magmatism for at least 40 My, yet the nature and distribution of intrusive magmas and their relation to subsequent East Africa rifting remain poorly characterized. This paper presents a 3D shear (S) - wave velocity structure of the crust and uppermost mantle beneath the northern sectors of the East African rift and the dynamically-supported Ethiopian Plateau. We apply a Bayesian inversion of group and phase velocity dispersion curves for periods 5-40 s extracted from the ambient noise tomography of data from over 125 broadband seismic stations, and we identify seismic discontinuities using autocorrelation of P -wave coda. The resulting crustal structure affecting much of the Main Ethiopian Rift (MER) indicates a pronounced low S -wave velocity lower crust (-3.6 km/s) that becomes thinner towards the northeast rising to almost the same depth level (-20 km) as the base crust beneath the Afar triple junction zone. We also find high velocity features in the crust and uppermost mantle beneath the Afar rift axes, the current locus of strain and volcanism, that may indicate voluminous new basaltic crust. Our Moho-depth map indicates that the entire Afar Depression is underlain by crust thinner than 25 km, whereas the MER and central Ethiopian plateau are underlain by low S -wave velocity crust thicker than 35 km. These patterns suggest active underplating beneath the largely unfaulted plateau, in contrast to the efficient magmatic feeder system supplying a narrow zone of incipient seafloor spreading in the Afar depression. Within the uppermost mantle we report evidence of a localized asthenospheric upwelling beneath the western part of the plateau southeast of Lake Tana, overlying a cooled magma body within the upper crust. A broader low-velocity uppermost mantle underlies the crust beneath the Western Plateau. These observations attest to active mantle upwelling, heating, and melt intrusion at relatively different length scales beneath the plateau in agreement with the ongoing active strains reported away from the rift zones. At 45-60 km depth beneath the rift and its shoulders, we observe a fast lid (4.2-4.4 km/s). Beneath the plateau, upper mantle velocity highs that are at least 5 km below the Moho are observed. These areas have most likely experienced prolonged magma extraction and may mark highly depleted areas.

The Turkana Depression separates the uplifted Ethiopian and East African Plateaus. It was the site, in Mesozoic times, of a failed episode of NE–SW-oriented rifting (the Anza Rift), but now hosts E–W-oriented Nubia–Somalia separation at the junction between the Main Ethiopian Rift in the north and the Eastern Rift to the south. However, the time-integrated effect of these rifting phases on crustal and lithospheric mantle architecture and thermal structure is poorly understood. Utilising data from new seismograph networks in the Turkana Depression and northern Tanzania Craton, we produce a detailed anisotropic crustal and uppermost mantle shear-wave velocity model of the region. Within the Tanzania Craton, slightly lower uppermost mantle wavespeeds (4.4–4.5 km/s) compared to neighbouring regions, and coincident rift-parallel crustal anisotropy, imply the Nyanza Rift developed in relatively weak mobile belt lithosphere between two refractory Archean blocks. At upper-crustal (≲10 km) depths in the Turkana Depression, the slowest velocities (≲3.2 km/s) are attributed to thick Mesozoic-age sedimentary basins. Nowhere within the Depression is the mid-to-lower crust or lithospheric mantle associated with wavespeeds as slow, or seismic anisotropy as strong, as that observed below the melt-rich central and northern Main Ethiopian Rift (MER) and Ethiopian Plateau further north. High upper mantle wavespeeds (≳4.5 km/s), coinciding with the broadening of MER-rifting into southern Ethiopia, confirm the presence of refractory Proterozoic lithosphere acting as a rheological boundary to rift development. Thinned crustal zones associated with failed Mesozoic Anza rifting are also underlain by fast wavespeed (>4.5 km/s) mantle lithosphere, implying this area has resisted significant thermomechanical modification from Miocene-Recent extension and magmatism. Pre-existing crustal thin zones do not, therefore, necessarily represent zones of plate-weakness where subsequent phases of rifting will develop.

Continental rifting is currently active in East Africa, where breakup of the African continent is generally occurring in relatively focused rift zones within two uplifted plateaus, with magma intrusions the primary mechanism for strain accommodation throughout the crust and mantle lithosphere. Linking the two narrow rift valleys is the low-lying, and as-yet poorly studied Turkana Depression - an unusually broad 300km-wide region of diffuse faulting, seismicity and magmatism. How the East African Rift has developed here remains elusive and is complicated by the fact the Depression was variably stretched by several superposed episodes of failed rifting since the Mesozoic. Utilising data from the NSF-NERC-funded TRAILS seismic network, we produce the first detailed crustal and uppermost-mantle shear-wave velocity model below the Turkana Depression, illuminating Moho and lithosphere-asthenosphere boundary topography that ultimately shed light on rift development in a multiply-rifted region. We find Turkana’s lithosphere is relatively melt-poor, unlike the Ethiopian rift and Plateau further north, which have undergone extensive lithospheric modification by voluminous Cenozoic flood-basalt magmatism and magma-assisted rifting. The lower crust below rift zones in Turkana is not associated with markedly slow (melt) or fast (cooled gabbroic intrusions) wavespeeds suggesting magmatic extension has not dominated rift development in Turkana. Throughout the Depression, the thinnest crust resides within failed Mesozoic rift zones which the present-day East African Rift appears to circumnavigate, not exploit. Fast uppermost mantle wavespeeds below the thinnest crustal regions indicate post-Mesozoic rifting, re-equilibrated and possibly melt-depleted mantle lithosphere, which now renders the plate stronger and more refractory than regions not previously rifted. Refractory Proterozoic lithosphere also present in southern Ethiopia may have influenced strain localisation and the broad, complex rift zone between Ethiopia and Kenya.

The Southeastern portion of the East African Rift System reactivates Mesozoic transform faults marking the separation of Madagascar from Africa in the Western Indian Ocean. Earlier studies noted the reactivation of the Davie Fracture Zone in oceanic lithosphere as a seismically active extensional fault, and new 3D seismic reflection data and exploration wells provide unprecedented detail on the kinematics of the sub-parallel Seagap fault zone in continental/transitional crust landward of the ocean-continent transition. We reconstruct the evolution of the seismically active Seagap fault zone, a 400-km-long crustal structure affecting the Tanzania margin, from the late Eocene to the present day. The Seagap fault zone is represented by large-scale localized structures affecting the seafloor and displaying growth geometries across most of the Miocene sediments. The continuous tectonic activity evident by our seismic mapping, as well as 2D deep seismic data from literature, suggests that from the Middle-Late Jurassic until 125 Ma, the Seagap fault acted as a regional structure parallel to, and coeval with, the dextral Davie Fracture Zone. The Seagap fault then remained active after the cessation of both seafloor spreading in the Somali basin and strike-slip activity on the Davie Fracture Zone, till nowaday. Its architecture is structurally expressed through the sequence of releasing and restraining bends dating back at least to the early Neogene. Seismic sections and horizon maps indicate that those restraining bends are generated by strike-slip reactivation of Cretaceous structures till the Miocene. Finally based on the interpretation of edge-enhanced reflection seismic surfaces and seafloor data, we shows that, by the late Neogene, the Seagap fault zone switched to normal fault behaviour. We discuss the Seagap fault's geological and kinematic significance through time and its current role within the microplate system in the framework of the East African rift, as well as implications for the evolution and re-activation of structures along sheared margins. The newly integrated datasets reveal the polyphase deformation of this margin, highlighting its complex evolution and the implications for depositional fairways and structural trap and seal changes through time, as well as potential hazards.

Feedbacks between chemical, physical, and biological processes at rift zones evolve through various time (seconds to 10(7) yrs) and spatial (microns to 10(6) m) scales. Consideration of these scales is needed to tap rift energy, water, and mineral resources safely and equitably while preserving biodiversity in these changing settings.

Constraints on chemical heterogeneities in the upper mantle may be derived from studying the seismically observable impedance contrasts that they produce. Away from subduction zones, several causal mechanisms are possible to explain the intermittently observed X‐discontinuity (X) at 230–350 km depth: the coesite‐stishovite phase transition, the enstatite to clinoenstatite phase transition, and/or carbonated silicate melting, all requiring a local enrichment of basalt. Africa hosts a broad range of terranes, from Precambrian cores to Cenozoic hotspots with or without lowermost mantle origins. With the absence of subduction below the margins of the African plate for >0.5 Ga, Africa presents an ideal study locale to explore the origins of the X. Traditional receiver function (RF) approaches used to map seismic discontinuities, such as common conversion‐point stacking, ignore slowness information crucial for discriminating converted upper mantle phases from surface multiples. By manually assessing depth and slowness stacks for 1° radius overlapping bins, normalized vote mapping of RF stacks is used to robustly assess the spatial distribution of converted upper mantle phases. The X is mapped beneath Africa at 233–340 km depth, revealing patches of heterogeneity proximal to mantle upwellings in Afar, Canaries, Cape Verde, East Africa, Hoggar, and Réunion with further observations beneath Cameroon, Madagascar, and Morocco. There is a lack of an X beneath southern Africa and strikingly, the magmatic eastern rift branch of the southern East African Rift. With no relationships existing between depth and amplitudes of observed X and estimated mantle temperatures, multiple causal mechanisms are required across a range of continental geodynamic settings.