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Caldera systems are often restless and experience pulses of uplift and subsidence, with a weak, but significant link to eruption. Characterizing the spatial and temporal patterns of deformation episodes provides insight into the processes responsible for unrest and the architecture of magmatic and hydrothermal systems. Here we combine interferometric synthetic aperture radar images with data from Global Positioning System and a network of seismometers at a continental rift caldera Corbetti, Ethiopia. We document inflation that started mid‐2009 and is ongoing as of 2017, with associated seismicity. We investigate the temporal evolution of the deformation source using a Hastings‐Metropolis algorithm to estimate posterior probability density functions for source model parameters and use the Akaike information criterion to inform model selection. Testing rectangular dislocation and point sources, we find a point source at a depth of 6.6 km (95% confidence: 6.3 − 6.8 km) provides the statistically justified fit. The location of this source is coincident with a conductive anomaly derived from magnetotelluric measurements. We use a joint inversion of two geodetic data sets to produce a time series, which shows a volume input of 1.0 × 107m3/year. This is the first observation of a prolonged period of magma reservoir growth in the Main Ethiopian Rift and has implications for hazard assessment and monitoring. Corbetti is < 20 km from two major population centers and has estimated return periods of ∼500 and ∼900 years for lava flows and Plinian eruptions, respectively. Our results highlight the need for long‐term geodetic monitoring and the application of statistically robust methods to characterize deformation sources. Corbetti caldera, Ethiopia, has been uplifting continuously since mid‐2009 at a vertical rate of ∼7 cm/yearThe uplift at Corbetti can be modeled by an inflating Mogi source at depth ∼6.6 km, with a consistent volume change of 107m3/yearThe deformation at Corbetti is likely caused by a magmatic system

Continental rifting is a fundamental component of plate tectonics. Recent studies have highlighted the importance of magmatic activity in accommodating extension during late‐stage rifting, yet the mechanisms by which crustal thinning occurs are less clear. The Red Sea rift in Northern Afar presents an opportunity to study the final stages of continental rifting as these active processes are exposed subaerially. Between February 2011 and February 2013 two seismic networks were installed in Ethiopia and Eritrea. We locate 4,951 earthquakes, classify them by frequency content, and calculate 31 focal mechanisms. Results show that seismicity is focused at the rift axis and the western marginal graben. Rift axis seismicity accounts for ∼64% of the seismic moment release and exhibits a swarm‐like behavior. In contrast, seismicity at the marginal graben is characterized by high‐frequency earthquakes that occur at a constant rate. Results suggest that the rift axis remains the primary locus of seismicity. Low‐frequency earthquakes, indicative of magmatic activity, highlight the presence of a magma complex ∼12 km beneath Alu‐Dalafilla at the rift axis. Seismicity at the marginal graben predominantly occurs on westward dipping, antithetic faults. Focal mechanisms show that this seismicity is accommodating E‐W extension. We suggest that the seismic activity at the marginal graben is either caused by upper crustal faulting accommodating enhanced crustal thinning beneath Northern Afar or as a result of flexural faulting between the rift and plateau. This seismicity is occurring in conjunction with magmatic extension at the rift axis, which accommodates the majority of long‐term extension. Seismicity in Northern Afar is focused at the rift axis and western rift marginLow‐frequency seismicity at the rift axis shows evidence for an ∼12 km deep magma complexSeismicity at the western rift margin is caused by faulting associated with enhanced crustal thinning or crustal flexure

In magma‐rich rifts, normal faulting is commonly thought to be induced by dike intrusions. However, whether fault slip occurs purely tectonically is unclear. An earthquake sequence starting with a Mw5.5 earthquake occurred in December 2022 in northern Afar, a continental rift near breakup. InSAR measurements show that seismicity was caused by normal faulting alone, without involvement of magma movements. Our best‐fit InSAR models show that conjugate faults ruptured during the seismic sequence with mainly normal dip‐slip and total deformation corresponding to a Mw5.7 event, in agreement with local seismic recordings. Our models show that tectonic faulting accommodates 26 cm of extension corresponding to ∼30 years of plate spreading without any link to magma. Our observations point toward significant along‐rift variation in the proportion of extension from faulting, potentially caused by along‐rift variations in rate of extension and/or from a spatially and temporally segmented supply of magma. The Earth's continents move away from each other forming a rift valley between the two separating tectonic plates. In mature stages of the continental rupture process, it is commonly accepted that plate separation occurs from the migration of molten rock (magma) toward the Earth's surface in narrow zones beneath the rift valley. Brittle faulting of the plate was thought to be less important. In this study we analyze the recent earthquake sequence of 26–28 December 2022 in the volcanically active northern Afar rift of Ethiopia. We show that, while the sequence occurred within the rift valley, it was caused by pure faulting without any involvement of magma migrations. These observations are unexpected and show that faults alone can assist plate separation even in mature and magma‐rich rift valleys. A seismic sequence with a Mw5.5 mainshock occurred in the Bada region of northern Afar rift between 26 and 28 December 2022InSAR models and seismicity revealed co‐seismic deformation along conjugate faults with no involvement of magma motionsOur observations show that extension can be achieved through purely tectonic processes in magma‐rich continental rifts A seismic sequence with a Mw5.5 mainshock occurred in the Bada region of northern Afar rift between 26 and 28 December 2022 InSAR models and seismicity revealed co‐seismic deformation along conjugate faults with no involvement of magma motions Our observations show that extension can be achieved through purely tectonic processes in magma‐rich continental rifts

There is a long-standing debate over how many and what types of plumes underlie the East African Rift and whether they do or do not drive its extension and consequent magmatism and seismicity. Here we present a new tomographic study of relative teleseismic Sand SKSresiduals that expands the resolution from previous regional studies below the northern East African Rift to image structure from the surface to the base of the transition zone. The images reveal two low-velocity clusters, below Afar and west of the Main Ethiopian Rift, that extend throughout the upper mantle and comprise several smaller-scale (about 100?km diameter), low-velocity features. These structures support those of our recent Ptomographic study below the region. The relative magnitude of Sto Presiduals is around 3.5, which is consistent with a predominantly thermal nature of the anomalies. The Sand Pvelocity anomalies in the low-velocity clusters can be explained by similar excess temperatures in the range of 100–200°C, consistent with temperatures inferred from other seismic, geochemical, and petrological studies. Somewhat stronger VSanomalies below Afar than west of the Main Ethiopian Rift may include an expression of volatiles and/or melt in this region. These results, together with a comparison with previous larger-scale tomographic models, indicate that these structures are likely small-scale upwellings with mild excess temperatures, rising from a regional thermal boundary layer at the base of the upper mantle. It is debated what causes plates to break up, as the African Plate is currently doing along the East African Rift. Many previous studies have implicated a hot upwelling from about 3000 km deep in the mantle as the main force, as well as the source of the volcanism along the rift. We performed a detailed seismic imaging study below the Northern East African Rift using so-called shear (S) waves, emitted by far-away earthquakes. Our study reveals that there is not a single large (hundreds of km in diameter) upwelling below the region, but rather there are, at least above 700 km depth where our images have resolution, several small ones (with diameters of 100-200 km). This supports the results from a previous study using compressional (P) waves. The two wave types have different sensitivities to rock temperature and composition. The P and S studies together constrain the temperatures of the upwellings below northern East Africa to be about 100–200 degrees hotter than usual mantle temperatures, consistent with them being the source of many of the volcanic rocks that have been found in the region. Swave tomography shows multiple upper mantle upwellings below the northern East African Rift as previously proposed using PtomographyBoth S and P anomalies are consistent with a dominantly thermal signature of 100-200° excess temperatureThe complex transition zone structure may well connect to lower mantle roots revealed in large-scale tomography

A major rifting episode began in the Afar region of northern Ethiopia in September 2005. Over a 10-day period, c.2.5 km3of magma were intruded into the upper crust along a 60 km-long dyke separating the Arabian and Nubian plates. There was an intense seismic swarm and a small rhyolitic eruption; extension of up to 10 m occurred across the rift segment. Over the next five years, a further 13 dyke intrusions caused continued extension, eruptions and seismicity. The activity in Afar led to a renewed international focus on the role of magmatism in rifting, with major collaborative projects involving researchers from Ethiopia, the UK, the USA, France, Italy and New Zealand working in Afar and Ethiopia to study the ongoing activity and to place it in a broader context. This book brings together articles that explore the role of magmatism in rifting, from the initiation of continental break-up through to full seafloor spreading. We also explore the hazards related to rifting and the associated volcanism. This renewed focus on magmatism and its role in rifting has implications for our understanding of how continents break-up and the associated distribution of resources in rift basins and continental margins.

Temporary broadband seismic networks deployed from 2007 to 2011 around the Afar triple junction of the East African Rift System provide insights into seismicity patterns of the actively deforming crust around the 1.86 km3impounded lake system behind the Tendaho dam. The observed seismicity correlates well with the active magmatic centres around central Afar. The area around the dam site is characterized by a network of intersecting NNE- and NW-trending faults. Seismicity clusters observed in the specified time interval indicate that both fault sets are active and are potential sources of seismogenic hazards. The dam neighbourhood is naturally active and it is a challenge to associate the observed seismic activity to either a change in magmato-tectonic conditions or attribute it to the influence of reservoir load. It is evident that the dam region experiences high levels of seismic and volcano-tectonic unrest, regardless of the origin of the activity. The spatial overlap of narrow zones of crustal seismicity and upper mantle low velocity zones observed in S-wave tomography models suggests that melt production zones guide the distribution of strain during continental rupture. Given its volcanically and seismically active setting, the Tendaho dam site and the surrounding region require continuous monitoring for the safety of downstream populations and development infrastructures in the Afar National Regional State of Ethiopia.

During the breakup of continents in magmatic settings, the extension of the rift valley is commonly assumed to initially occur by border faulting and progressively migrate in space and time toward the spreading axis. Magmatic processes near the rift flanks are commonly ignored. We present phase velocity maps of the crust and uppermost mantle of the conjugate margins of the southern Red Sea (Afar and Yemen) using ambient noise tomography to constrain crustal modification during breakup. Our images show that the low seismic velocities characterize not only the upper crust beneath the axial volcanic systems but also both upper and lower crust beneath the rift flanks where ongoing volcanism and hydrothermal activity occur at the surface. Magmatic modification of the crust beneath rift flanks likely occurs for a protracted period of time during the breakup process and may persist through to early seafloor spreading. Crustal and upper mantle structures are characterized in Red Sea and AfarMagmatic processes are currently modifying the crust of the Red Sea flanksRift‐flank magmatism can persist after breakup

Integrated inversions of short-period P, broadband P, and long-period P &s waves are done for fault mechanisms, focal depths, seismic moments, and source-time functions from the largest four earthquakes of the 1985 and 1987 earthquake sequence in south-western Ethiopia. These earthquakes had similar normal-faulting mechanisms. The general trends of the fault planes follow the Main Ethiopian Rift which is in agreement with foreshock-aftershock distribution, surface breaks and geology. Despite the morphological discontinuity of the Main Ethiopian Rift at its southern tip, the mode of deformation of the continental crust under study shows its extension southward. There are no significant strike-slip components trending NW–SE in all the mechanisms which would have been associated with the Aswa Fault Zone in southern Sudan or Anza Rift in northern Kenya. We also infer that the relatively broad fracture zone at the southern extreme of the Main Ethiopian Rift demonstrates the early stage of the break-up between the Nubia and Somalia plates in comparison with the Main Ethiopian Rift proper and the Afar Depression. The main shock of the sequence (Mw= 6.3) ruptured at a depth of 6.8 km, shallower than expected since the depth of earthquakes generally increase southward from the Afar Depression. The shallow depth of earthquake occurrence is supported by surface deformations with an overall trend in the direction of the Main Ethiopian Rift.

Studying the mechanisms of interaction between rift segments is key to understanding the kinematics of plate boundaries in continental rifts. However, the spatial and temporal evolution of deformation at rift linkage zones is rarely observed directly. Here, we combine InSAR data spanning 2005–2010 and 2014–2019 from ENVISAT and Sentinel‐1 satellites, respectively, with local seismicity from the Afar rift to investigate the plate‐boundary kinematics of the Afrera linkage zone, the junction between the Erta Ale and Tat Ali magmatic segments in Northern Afar (Ethiopia). We obtain time‐series of cumulative InSAR Line‐Of‐Sight (LOS) displacements that show deformation is accommodated by a series of active en‐echelonfaults striking ∼NS and characterized by normal slip associated with a left‐lateral strike‐slip component. Additionally, we observe spatial variation in fault behavior with stick‐slip and creep. The faults in the center of the linkage zone behave primarily in a stick‐slip mode (with abrupt fault displacements up to ∼40 mm) and fault motions are associated with earthquakes of ML> 5. Conversely, faults at the edge of the linkage zone, near the magmatic segments, show creep and some stick‐slip behavior (with cumulative LOS displacement up to ∼30–40 mm over a ∼5‐year period) accompanied by low‐level seismicity. Some of the creeping faults are also spatially associated with hydrothermal springs. We interpret that the temporal behavior of the faults in the linkage zone is controlled by the interplay between tectonic extension, high heat flows, and fluid circulation near the magmatic segments where creeping of some faults is favored. The exterior of the Earth is torn apart along mid‐ocean ridges where magma rises and new oceanic crust is created. Mid‐ocean ridges have an unmissable zig‐zag pattern because while some portions called ridge segments are being torn apart others called offsets, slide past each other. However, how the Earth deforms in these offsets is today poorly understood. The Afar region is the perfect place to address this open question as it is one of the few pales where a mid‐ocean ridge is emerged and the segments and offsets can be observed on‐land. In this study, we combine satellite and earthquakes measurements to film how the surface of the Earth moves in an offset. We show that the network of fractures at the surface of an offset can either move with sudden motions generating major earthquakes or slip continuously over years and produce many smaller earthquakes. Our results provide one of the few direct observations of the different type of motion of the Earth in an offset of the mid‐ocean ridge system. InSAR time‐series and seismicity analyses of deformation at the Afrera Plain linkage zone in Northern Afar, EthiopiaTime‐series show fault slip accommodated through stick‐slip and creep along en‐echelon NS‐striking faultsVarying fault behavior could be influenced by elevated heat flows and hydrothermal circulation near the magmatic segments InSAR time‐series and seismicity analyses of deformation at the Afrera Plain linkage zone in Northern Afar, Ethiopia Time‐series show fault slip accommodated through stick‐slip and creep along en‐echelon NS‐striking faults Varying fault behavior could be influenced by elevated heat flows and hydrothermal circulation near the magmatic segments

Lower‐crustal seismicity is commonly observed in continental rift zones despite the crust at such depths being ductile enough to prohibit brittle failure. The source of such deep seismicity across the East African Rift remains an outstanding question. Here we present analysis of an isolated cluster of lower‐crustal earthquakes located on the eastern border faults of the Main Ethiopian Rift, near the Corbetti caldera. Lower‐crustal earthquakes have not previously been observed in this area. Phase arrival times were determined using an automated picking approach based on continuous wavelet transform and statistical changepoint detection methods. We overcome misinterpretations from large hypocenter depth errors by considering mixture distributions for all events and their associated uncertainties. These mixture distributions represent probability density functions of any event occurring at a given depth. The mixture distribution mode for a variety of different velocity models and error parameters remained stable at a depth of 28–32 km, with the vast majority of maximum likelihood estimates for individual hypocenters located at depths of 25–35 km. Most events occur over a 2 month period, with 90% of cumulative seismic moment occurring during March and April 2012. The ephemeral and localized nature of this seismicity, combined with low event magnitudes and regional hydrothermal/magmatic activity, suggests that these lower‐crustal events are likely related to fluid or magmatic processes. Plausible mechanisms include the movement of magma and/or exsolution of volatiles at depth causing transient high strain rates and pore fluid pressures that induce seismicity. A sequence of lower‐crustal seismicity is identified 30 km east of Corbetti caldera on the eastern border faults of the Main Ethiopian RiftMixture distributions are used to overcome misinterpretations from large uncertainty in individual event locationsSpatial and temporal characteristics indicate that the source of this seismicity relates to fluid or magmatic processes

We provide insights into the tectonics of the Asela‐Langano margin, at the eastern boundary of the central Main Ethiopian Rift, East Africa, by combining field structural data, remote sensing, analysis of the distribution of faults, new dating of faulted material, and analysis of seismicity. The area is characterized by the occurrence of two fault sets: boundary and axial (Wonji) faults, oriented NE‐SW and NNE‐SSW, respectively. Boundary faults show a complex arrangement in the lake Langano area where they display a rhomboidal pattern, due to the presence of NW‐SE‐trending structures, likely related to preexisting transverse fabrics (the so‐called Langano Rhomboidal Fault System). Overall, our analysis supports a structure of the margin characterized by a monocline affected by a series of minor horsts and grabens; this confirms a marked asymmetry of the central Main Ethiopian Rift, with a master fault system on the opposite, western margin. Cumulative paleostress analysis indicates an overall N115°E extension across the Asela‐Langano margin; however, a local variation of the extension direction from axial (Wonji) faults (∼N90°E) to the boundary faults (∼N115°E) can be observed, pointing to a stress reorientation at rift margins. New 14C dating of faulted material and seismicity analysis indicate Late Pleistocene–Holocene and current activity on several normal faults affecting the margin. This suggests that extensional deformation in the central Main Ethiopian Rift is accommodated at the rift margins, with subordinate activity on axial faults, supporting that this rift sector reflects an intermediate stage of rift evolution. The motion of tectonic plates away from each other (extension) in rift valleys, such as in East Africa, causes earthquakes, fissuring and faulting of Earth, and volcanic activity. As a rift valley grows, the regions of most intense earthquake and volcanic activity typically changes through time. In this contribution, we combine several different approaches (analysis of satellite images and surface topography, field observations of geology and faults, and analysis of recent earthquakes) to understand the tectonics of the East African rift in Ethiopia. We identify which faults are most active using the geology and location of earthquakes and also measure the direction in which the faults move. Recent earthquakes include a magnitude 5.3 earthquake in January 2017. We also show that the youngest and currently active faults are associated with volcanoes in the rift valley. Overall, our results improve the knowledge of the deformation, seismicity, and volcanism of the rift valley in Ethiopia, which can help scientists understand how a rift valley develops and which regions are currently hazardous. We provide new insights into the architecture and the recent and active tectonics of the Asela‐Langano margin, central Main Ethiopian RiftArchitecture of the margin characterized by a monocline affected by a series of minor horsts and grabens confirms a marked rift asymmetryLate Pleistocene–Holocene and current activity on several normal faults affects the margin, where stress reorientation is observed

The Boset magmatic segment (BMS) of the northern Main Ethiopian Rift (MER) is an ideal natural laboratory to investigate the kinematics, interaction, and rates of activity within a fault network in a magma‐rich rift. In this paper we take advantage of the availability of (1) high‐resolution remote sensing data (LiDAR, ASTER); (2) absolute age chronology on offset reference surfaces; and (3) well‐exposed active normal fault arrays to place new constraints on rift kinematics and strain distribution, and to quantify the architecture and fault slip rates at different temporal scales within a magmatic segment. We found that the rift border faults strike approximately NE, while the younger faults in the rift segments strike NNE. Analyses of geometric rift parameters show that the axial active part of the rift is transtensional with an increase of the shear component northward. The fault displacement analyses and displacement:length ratios increase toward the segment tips, suggesting a significant contribution of fault growth by linkage. In contrast, magmatism is focused on the segment center and localized to a narrow zone. Estimated fault slip rates vary, with rates of up to ~0.37 mm/year in ~0.3 Ma old rift floor deposits, whereas higher rates of up to ~4.4 mm/year are observed for faults cutting through ~6 Ka lavas. The difference in slip rates indicates short‐term variability or a very active recent episode compared to long‐term low average slip rates. Large‐scale obliquity in the northern MER increases toward Afar with transtensional kinematicsThe Boset magmatic segment is characterized by two main NNE orientated fault zones, bounding a nested grabenMaximum slip rates are ~0.37 mm/year in ~300 Ka volcanic deposits and ~4.3 mm/year offsetting ~6 Ka lavas of Boset

Spatial and temporal variations of seismic energy release and b-value are investigated in the Horn of Africa. The results indicate that the area around the Afar Depression and southern Sudan is at a higher stress level than the southern Red Sea and Gulf of Aden. The distribution of earthquakes in the vicinity of Afar shows a systematic pattern and suggests the existence of two microplates (blocks) centred about the Danakil and Aisha horsts.