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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‐echelon faults 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. Plain Language Summary: 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. Key Points: 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 [ABSTRACT FROM AUTHOR]

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. Plain Language Summary: 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. Key Points: 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 [ABSTRACT FROM AUTHOR]

We investigate rare seismicity in the neighborhood of the Fentale volcano, main Ethiopian rift that occurred in spring 2015 using data recorded by the Ethiopian Seismic Station Network. Over 1350 earthquakes are located and a seismic swarm is observed to the northeast of Fentale volcano, with the largest earthquake having a magnitude of 4.3 ML. Several VT (volcano-tectonic) and LP (long-period) events are observed in the swarm, indicating that it is induced by magmatic intrusion, consistent with dike-induced deformation in the same area inferred from satellite geodesy. The seismic activity commenced at about 40 km depth and migrated southwestward as it shallowed, towards Fentale volcano, suggesting that the dike feeding system might be influenced by the magma rich Afar Depression further to the northeast rather than the adjacent Fentale volcano. An earlier cluster of seismicity in the same area was recorded by a temporary deployment of seismic stations that ran from November 2001 to January 2003; extensive clusters of less well recorded seismic activity in the region occurred in June 1989, January–February 1981, October–November 2003, and 2004. Such frequent seismicity at the Fentale Volcanic Complex coupled with the adjacent fast-growing Lake Basaka poses an eminent and significant risk to Ethiopia's access to Djibouti port, its most important commercial route. This should be a wakeup call to concerned stakeholders to take precautionary measures by developing risk management and rapid response strategies. • We analyzed the March and April 2015 earthquake swarm that occurred around Tinish Fentale which is found in the northern main Ethiopian rift. • We located more than 1350 earthquakes with maximum magnitude 4.3 ML. Our investigation shows that the activity is caused by dike intrusion. • The cluster of the seismic activity is shown to be closer to Ethiopia's main access road to the port of Djibouti which poses a geohazard risk. [ABSTRACT FROM AUTHOR]

Abstract: 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 × 107 m3/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. [ABSTRACT FROM AUTHOR]

Abstract: 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. [ABSTRACT FROM AUTHOR]

Seismic hazard calculation is carried out for the Horn of Africa region (0°–20° N and 30°–50°E) based on the probabilistic seismic hazard analysis (PSHA) method. The earthquakes catalogue data obtained from different sources were compiled, homogenized to M w magnitude scale and declustered to remove the dependent events as required by Poisson earthquake source model. The seismotectonic map of the study area that avails from recent studies is used for area sources zonation. For assessing the seismic hazard, the study area was divided into small grids of size 0.5° × 0.5°, and the hazard parameters were calculated at the center of each of these grid cells by considering contributions from all seismic sources. Peak Ground Acceleration (PGA) corresponding to 10% and 2% probability of exceedance in 50 years were calculated for all the grid points using generic rock site with Vs = 760 m/s. Obtained values vary from 0.0 to 0.18 g and 0.0–0.35 g for 475 and 2475 return periods, respectively. The corresponding contour maps showing the spatial variation of PGA values for the two return periods are presented here. Uniform hazard response spectrum (UHRS) for 10% and 2% probability of exceedance in 50 years and hazard curves for PGA and 0.2 s spectral acceleration (Sa) all at rock site are developed for the city of Addis Ababa. The hazard map of this study corresponding to the 475 return periods has already been used to update and produce the 3rd generation building code of Ethiopia. [ABSTRACT FROM AUTHOR]

Abstract: In August 2002, there was high seismic activity in Afar concentrated at the plateau margin of the northern Ethiopian rift east of Mekele, near the western part of the Danakil microplate. The spatial and temporal distributions of this seismic activity over four weeks indicate the NNW propagation of the Gulf of Aden rift across the Afar Depression towards the western Ethiopian plateau. Fault plane solutions for six larger earthquakes from the August 2002 sequence are estimated from moment tensor inversion of local broadband waveform data. The results show only normal faulting on NNW trending and NE dipping faults, which agree with tectonics of the area and distribution of aftershocks. No strike-slip component is observed in any of our fault plane solutions or those of other workers including Harvard CMT solutions in the region. Such motion would be indicative of oblique-slip deformation between the Nubian plate and the Danakil microplate consistent with counter-clockwise rotation of the microplate. Hypocentral depths of well-constrained events are 5–7km, which is the approximate elastic plate thickness in the Main Ethiopian rift, possibly indicating the depth to the brittle–ductile transition zone in this part of the Afar Depression. The shallowness of the depth estimates agree with the macroseismic reports available from a wide area in northern Ethiopia. Potential future shallow crustal deformation may cause significant loss of human life and damage to property in the densely populated highland region around Mekele unless measures are taken in improving building standards. The b-value for this sequence is estimated to be 0.66 using a least squares fit, while it is 0.67±0.16 from a maximum-likelihood approach. This estimated b-value is low or the frequency of occurrence of relatively larger magnitude events is high indicating that it is a highly stressed region as evidenced by the recent increase of the seismicity in the area. [Copyright &y& Elsevier]