Atalay Ayele - Academia.edu (original) (raw)

Papers by Atalay Ayele

Geochemistry, Geophysics, Geosystems, 2021

Key Points • We studied fault activity and kinematics at the Western Afar Margin using seismicity... more Key Points • We studied fault activity and kinematics at the Western Afar Margin using seismicity and InSAR. • We observed a seismic sequence occurring in the lower crust along both west-and east-dipping faults. • Deep seismicity could be caused by fluid migration in the lower crust.

SINET: Ethiopian Journal of Science, 2005

Together with the three component short period WWSSN analog station operating at the Geophysical ... more Together with the three component short period WWSSN analog station operating at the Geophysical Observatory (AAE), five seismic stations are running in the country. FURI is one of the four three-component digital stations with a GURALP CMG 3T and STS1 broadband sensors. The other three seismic stations at Wendogenet, Dessie and Alemaya are equipped with Le-3d/5s seismometers with RefTek Data Acquisition Systems (DASs), which provide semi-broadband signals. Except AAE , all stations use GPS receivers for accurate timing and provide three-component digital record. Digital data facilitate quick interpretations of seismic signals using computers. The seismic stations are in a good position to date to monitor major seismic activities of the Ethiopian rift. The earthquake locations estimated using data from our own network are found to be reliable with reasonable accuracy. A total of 15 earthquakes are located in this pilot study of which only four are captured by the USGS (United States Geological Survey) bulletin and all lie along the rift in Afar and the main Ethiopian rift system.

Bulletin of the Seismological Society of America, 2010

Areas of active volcanism contain elaborate velocity structures that complicate interpretations o... more Areas of active volcanism contain elaborate velocity structures that complicate interpretations of earthquake source mechanisms. We examine the spectral characteristics of 805 earthquakes that immediately followed a large volume basaltic dike intrusion and associated silicic flank eruption of Dabbahu volcano in the Afar Depression as recorded on near-source seismometers. We use these results to quantify the contribution of scattering and attenuation to the observed spectra of low-frequency hybrid and volcano-tectonic earthquake clusters from beneath Dabbahu volcano and around the dike zone. We find strong variations in the signal amplitude and frequency content of earthquakes recorded at stations separated by as little as 2 km, caused by preferential attenuation of high frequencies depending on the vantage point. These observations imply that there are large impedance contrasts near the cooling, solidifying, and recently intruded dike. We estimate the intrinsic absorption attenuation coefficient, Q I , and inverse scattering length, g 0 , averaged over a 300-sq-km area beneath Dabbahu. Our results are consistent with the highest attenuation coefficients from studies of volcanic provinces in Italy (Q 1 I ≈ 0:02, g 0 ≈ 0:1 km 1 for a signal at 2 Hz). The magnitude of these two parameters indicates there are large impedance contrasts present in the area due to the recent intrusion of magma and associated fracturing.

Journal of Geophysical Research: Solid Earth, 2021

Geochemistry, Geophysics, Geosystems, 2020

Journal of Volcanology and Geothermal Research, 2018

Earth and Planetary Science Letters, 2019

The active magmatic processes beneath volcanoes in continental rifts is poorly understood. For ex... more The active magmatic processes beneath volcanoes in continental rifts is poorly understood. For example, until recently in the East African rift (EAR), the majority of the young volcanoes were thought to be inactive. More recent studies have shown that numerous volcanoes in the EAR are seismically active and deforming rapidly. However, an unambiguous sign of actively degassing magma hosted in shallow magma bodies has eluded most investigators. Here we present detailed analysis of the first low-frequency (LF) earthquake swarms to be observed in the Main Ethiopian Rift. The earthquakes locate to beneath Tullu Moye volcano *Manuscript Click here to view linked References and are directly related to the presence of a shallow magma body with a high fluid content. Using spectral modelling we show that the LF earthquakes appear to have low stress-drops (1-50 kPa) which we interpret in terms of low rupture velocities and high pore-fluid pressure. Careful relocation of the LF earthquakes place them approximately 4 km below the surface within one of two possible clusters. However, analysis of the correlation between earthquake waveforms show that each swarm contains a range of earthquake families and as such a diversity of earthquake source mechanisms. To explain these observations, we propose the seismicity is induced by H 2 O/CO 2 fluid pulses from the shallow magma body into a highly fractured region. Fluid pulses cause high pore fluid pressures, which also cause the low rupture velocities.

Bulletin of the Seismological Society of America, 2018

The earthquakes associated with continental deformation are spatially and temporally variable and... more The earthquakes associated with continental deformation are spatially and temporally variable and are fundamental in understanding fault activity and seismogenic hazards. We conduct K-means cluster analysis on seismicity in the African-Arabian rift systems to create the first computationally objective analysis of the pattern of earthquakes. We use seismic moment to compute spatial variations in maximum credible earthquake (Mcred) and likely time to the next major release of seismic energy. Our best-fit model has 32 clusters of ∼100-400 km in length, with cluster size decreasing northward along the rift and cluster boundaries correlating with major structural segmentation of the rift. Mcred varies between M w 5.2 and 7.4 across the whole dataset, with the highest values estimated in portions of the rift where the majority of extension is accommodated by seismogenic failure.

Journal of Geophysical Research: Solid Earth, 2018

Journal of Volcanology and Geothermal Research, 2018

Earth and Planetary Science Letters, 2018

In continental rifts structural heterogeneities, such as pre-existing faults and foliations, are ... more In continental rifts structural heterogeneities, such as pre-existing faults and foliations, are thought to influence shallow crustal processes, particularly the formation of rift faults, magma reservoirs and surface volcanism. We focus on the Corbetti caldera, in the southern central Main Ethiopian Rift. We measure the surface deformation between 22nd June 2007 and 25th March 2009 using ALOS and ENVISAT SAR interferograms and observe a semi-circular pattern of deformation bounded by a sharp linear feature cross-cutting the caldera, coincident with the caldera long axis. The signal reverses in sign but is not seasonal: from June to December 2007 the region south of this structure moves upwards 3 cm relative to the north, while from December 2007 until November 2008 it subsides by 2 cm. Comparison of data taken from two different satellite look directions show that the displacement is primarily vertical. We discuss potential mechanisms and conclude that this deformation is associated with pressure changes within a shallow (<1 km) fault-bounded hydrothermal reservoir prior to the onset of a phase of calderawide uplift. Analysis of the distribution of post-caldera vents and cones inside the caldera shows their locations are statistically consistent with this fault structure, indicating that the fault has also controlled the migration of magma from a reservoir to the surface over tens of thousands of years. Spatial patterns of seismicity are consistent with a cross-rift structure that extents outside the caldera and to a depth of ∼30 km, and patterns of seismic anisotropy suggests stress partitioning occurs across the structure. We discuss the possible nature of this structure, and conclude that it is most likely associated with the Goba-Bonga lineament, which cross-cuts and pre-dates the current rift. Our observations show that pre-rift structures play an important role in magma transport and shallow hydrothermal processes, and therefore they should not be neglected when discussing these processes.

Geochemistry, Geophysics, Geosystems, 2018

Earth and Planetary Science Letters, 2017

Journal of Volcanology and Geothermal Research, 2017

Bulletin of the Seismological Society of America, 2017

Nature Communications, 2016

Melting of the mantle during continental breakup leads to magmatic intrusion and volcanism, yet o... more Melting of the mantle during continental breakup leads to magmatic intrusion and volcanism, yet our understanding of the location and dominant mechanisms of melt generation in rifting environments is impeded by a paucity of direct observations of mantle melting. It is unclear when during the rifting process the segmented nature of magma supply typical of seafloor spreading initiates. Here, we use Rayleigh-wave tomography to construct a high-resolution absolute three-dimensional shear-wave velocity model of the upper 250 km beneath the Afar triple junction, imaging the mantle response during progressive continental breakup. Our model suggests melt production is highest and melting depths deepest early during continental breakup. Elevated melt production during continental rifting is likely due to localized thinning and melt focusing when the rift is narrow. In addition, we interpret segmented zones of melt supply beneath the rift, suggesting that buoyancy-driven active upwelling of the mantle initiates early during continental rifting.

Geological Society, London, Special Publications, 2016

A major rifting episode began in the Afar region of northern Ethiopia in September 2005. Over a 1... more 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 associa...

Bulletin of Volcanology, 2015

We present a synthesis of diverse observations of the first recorded eruption of Nabro volcano, E... more We present a synthesis of diverse observations of the first recorded eruption of Nabro volcano, Eritrea, which began on 12 June 2011. While no monitoring of the volcano was in effect at the time, it has been possible to reconstruct the nature and evolution of the eruption through analysis of regional seismological and infrasound data and satellite remote sensing data, supplemented by petrological analysis of erupted products and brief field surveys. The event is notable for the comparative rarity of recorded historical eruptions in the region and of caldera systems in general, for the prodigious quantity of SO 2 emitted into the atmosphere and the significant human impacts that ensued notwithstanding the low population density of the Afar region. It is also relevant in understanding the broader magmatic and tectonic significance of the volcanic massif of which Nabro forms a part and which strikes obliquely to the principal rifting directions in the Red Sea and northern Afar. The whole-rock compositions of the erupted lavas and tephra range from trachybasaltic to trachybasaltic andesite, and crystal-hosted melt inclusions contain up to 3,000 ppm of sulphur by weight. The eruption was preceded by significant seismicity, detected by regional networks of sensors and accompanied by sustained tremor. Substantial infrasound was recorded at distances of hundreds to thousands of kilometres from the vent, beginning at the onset of the eruption and continuing for weeks. Analysis of ground deformation suggests the eruption was fed by a shallow, NW-SE-trending dike, which is consistent with field and satellite observations of vent distributions. Despite lack of prior planning and preparedness for volcanic events in the country, rapid coordination of the emergency response mitigated the human costs of the eruption.

Nature Communications, 2011

Rifting of the continents leading to plate rupture occurs by a combination of mechanical deformat... more Rifting of the continents leading to plate rupture occurs by a combination of mechanical deformation and magma intrusion, yet the spatial and temporal scales over which these alternate mechanisms localize extensional strain remain controversial. Here we quantify anisotropy of the upper crust across the volcanically active Afar Triple Junction using shear-wave splitting from local earthquakes to evaluate the distribution and orientation of strain in a region of continental breakup. The pattern of s-wave splitting in Afar is best explained by anisotropy from deformation-related structures, with the dramatic change in splitting parameters into the rift axis from the increased density of dyke-induced faulting combined with a contribution from oriented melt pockets near volcanic centres. The lack of rift-perpendicular anisotropy in the lithosphere, and corroborating geoscientific evidence of extension dominated by dyking, provide strong evidence that magma intrusion achieves the majority of plate opening in this zone of incipient plate rupture.

Geochemistry, Geophysics, Geosystems, 2021

Key Points • We studied fault activity and kinematics at the Western Afar Margin using seismicity... more Key Points • We studied fault activity and kinematics at the Western Afar Margin using seismicity and InSAR. • We observed a seismic sequence occurring in the lower crust along both west-and east-dipping faults. • Deep seismicity could be caused by fluid migration in the lower crust.

SINET: Ethiopian Journal of Science, 2005

Together with the three component short period WWSSN analog station operating at the Geophysical ... more Together with the three component short period WWSSN analog station operating at the Geophysical Observatory (AAE), five seismic stations are running in the country. FURI is one of the four three-component digital stations with a GURALP CMG 3T and STS1 broadband sensors. The other three seismic stations at Wendogenet, Dessie and Alemaya are equipped with Le-3d/5s seismometers with RefTek Data Acquisition Systems (DASs), which provide semi-broadband signals. Except AAE , all stations use GPS receivers for accurate timing and provide three-component digital record. Digital data facilitate quick interpretations of seismic signals using computers. The seismic stations are in a good position to date to monitor major seismic activities of the Ethiopian rift. The earthquake locations estimated using data from our own network are found to be reliable with reasonable accuracy. A total of 15 earthquakes are located in this pilot study of which only four are captured by the USGS (United States Geological Survey) bulletin and all lie along the rift in Afar and the main Ethiopian rift system.

Bulletin of the Seismological Society of America, 2010

Areas of active volcanism contain elaborate velocity structures that complicate interpretations o... more Areas of active volcanism contain elaborate velocity structures that complicate interpretations of earthquake source mechanisms. We examine the spectral characteristics of 805 earthquakes that immediately followed a large volume basaltic dike intrusion and associated silicic flank eruption of Dabbahu volcano in the Afar Depression as recorded on near-source seismometers. We use these results to quantify the contribution of scattering and attenuation to the observed spectra of low-frequency hybrid and volcano-tectonic earthquake clusters from beneath Dabbahu volcano and around the dike zone. We find strong variations in the signal amplitude and frequency content of earthquakes recorded at stations separated by as little as 2 km, caused by preferential attenuation of high frequencies depending on the vantage point. These observations imply that there are large impedance contrasts near the cooling, solidifying, and recently intruded dike. We estimate the intrinsic absorption attenuation coefficient, Q I , and inverse scattering length, g 0 , averaged over a 300-sq-km area beneath Dabbahu. Our results are consistent with the highest attenuation coefficients from studies of volcanic provinces in Italy (Q 1 I ≈ 0:02, g 0 ≈ 0:1 km 1 for a signal at 2 Hz). The magnitude of these two parameters indicates there are large impedance contrasts present in the area due to the recent intrusion of magma and associated fracturing.

Journal of Geophysical Research: Solid Earth, 2021

Geochemistry, Geophysics, Geosystems, 2020

Journal of Volcanology and Geothermal Research, 2018

Earth and Planetary Science Letters, 2019

The active magmatic processes beneath volcanoes in continental rifts is poorly understood. For ex... more The active magmatic processes beneath volcanoes in continental rifts is poorly understood. For example, until recently in the East African rift (EAR), the majority of the young volcanoes were thought to be inactive. More recent studies have shown that numerous volcanoes in the EAR are seismically active and deforming rapidly. However, an unambiguous sign of actively degassing magma hosted in shallow magma bodies has eluded most investigators. Here we present detailed analysis of the first low-frequency (LF) earthquake swarms to be observed in the Main Ethiopian Rift. The earthquakes locate to beneath Tullu Moye volcano *Manuscript Click here to view linked References and are directly related to the presence of a shallow magma body with a high fluid content. Using spectral modelling we show that the LF earthquakes appear to have low stress-drops (1-50 kPa) which we interpret in terms of low rupture velocities and high pore-fluid pressure. Careful relocation of the LF earthquakes place them approximately 4 km below the surface within one of two possible clusters. However, analysis of the correlation between earthquake waveforms show that each swarm contains a range of earthquake families and as such a diversity of earthquake source mechanisms. To explain these observations, we propose the seismicity is induced by H 2 O/CO 2 fluid pulses from the shallow magma body into a highly fractured region. Fluid pulses cause high pore fluid pressures, which also cause the low rupture velocities.

Bulletin of the Seismological Society of America, 2018

The earthquakes associated with continental deformation are spatially and temporally variable and... more The earthquakes associated with continental deformation are spatially and temporally variable and are fundamental in understanding fault activity and seismogenic hazards. We conduct K-means cluster analysis on seismicity in the African-Arabian rift systems to create the first computationally objective analysis of the pattern of earthquakes. We use seismic moment to compute spatial variations in maximum credible earthquake (Mcred) and likely time to the next major release of seismic energy. Our best-fit model has 32 clusters of ∼100-400 km in length, with cluster size decreasing northward along the rift and cluster boundaries correlating with major structural segmentation of the rift. Mcred varies between M w 5.2 and 7.4 across the whole dataset, with the highest values estimated in portions of the rift where the majority of extension is accommodated by seismogenic failure.

Journal of Geophysical Research: Solid Earth, 2018

Journal of Volcanology and Geothermal Research, 2018

Earth and Planetary Science Letters, 2018

In continental rifts structural heterogeneities, such as pre-existing faults and foliations, are ... more In continental rifts structural heterogeneities, such as pre-existing faults and foliations, are thought to influence shallow crustal processes, particularly the formation of rift faults, magma reservoirs and surface volcanism. We focus on the Corbetti caldera, in the southern central Main Ethiopian Rift. We measure the surface deformation between 22nd June 2007 and 25th March 2009 using ALOS and ENVISAT SAR interferograms and observe a semi-circular pattern of deformation bounded by a sharp linear feature cross-cutting the caldera, coincident with the caldera long axis. The signal reverses in sign but is not seasonal: from June to December 2007 the region south of this structure moves upwards 3 cm relative to the north, while from December 2007 until November 2008 it subsides by 2 cm. Comparison of data taken from two different satellite look directions show that the displacement is primarily vertical. We discuss potential mechanisms and conclude that this deformation is associated with pressure changes within a shallow (<1 km) fault-bounded hydrothermal reservoir prior to the onset of a phase of calderawide uplift. Analysis of the distribution of post-caldera vents and cones inside the caldera shows their locations are statistically consistent with this fault structure, indicating that the fault has also controlled the migration of magma from a reservoir to the surface over tens of thousands of years. Spatial patterns of seismicity are consistent with a cross-rift structure that extents outside the caldera and to a depth of ∼30 km, and patterns of seismic anisotropy suggests stress partitioning occurs across the structure. We discuss the possible nature of this structure, and conclude that it is most likely associated with the Goba-Bonga lineament, which cross-cuts and pre-dates the current rift. Our observations show that pre-rift structures play an important role in magma transport and shallow hydrothermal processes, and therefore they should not be neglected when discussing these processes.

Geochemistry, Geophysics, Geosystems, 2018

Earth and Planetary Science Letters, 2017

Journal of Volcanology and Geothermal Research, 2017

Bulletin of the Seismological Society of America, 2017

Nature Communications, 2016

Melting of the mantle during continental breakup leads to magmatic intrusion and volcanism, yet o... more Melting of the mantle during continental breakup leads to magmatic intrusion and volcanism, yet our understanding of the location and dominant mechanisms of melt generation in rifting environments is impeded by a paucity of direct observations of mantle melting. It is unclear when during the rifting process the segmented nature of magma supply typical of seafloor spreading initiates. Here, we use Rayleigh-wave tomography to construct a high-resolution absolute three-dimensional shear-wave velocity model of the upper 250 km beneath the Afar triple junction, imaging the mantle response during progressive continental breakup. Our model suggests melt production is highest and melting depths deepest early during continental breakup. Elevated melt production during continental rifting is likely due to localized thinning and melt focusing when the rift is narrow. In addition, we interpret segmented zones of melt supply beneath the rift, suggesting that buoyancy-driven active upwelling of the mantle initiates early during continental rifting.

Geological Society, London, Special Publications, 2016

A major rifting episode began in the Afar region of northern Ethiopia in September 2005. Over a 1... more 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 associa...

Bulletin of Volcanology, 2015

We present a synthesis of diverse observations of the first recorded eruption of Nabro volcano, E... more We present a synthesis of diverse observations of the first recorded eruption of Nabro volcano, Eritrea, which began on 12 June 2011. While no monitoring of the volcano was in effect at the time, it has been possible to reconstruct the nature and evolution of the eruption through analysis of regional seismological and infrasound data and satellite remote sensing data, supplemented by petrological analysis of erupted products and brief field surveys. The event is notable for the comparative rarity of recorded historical eruptions in the region and of caldera systems in general, for the prodigious quantity of SO 2 emitted into the atmosphere and the significant human impacts that ensued notwithstanding the low population density of the Afar region. It is also relevant in understanding the broader magmatic and tectonic significance of the volcanic massif of which Nabro forms a part and which strikes obliquely to the principal rifting directions in the Red Sea and northern Afar. The whole-rock compositions of the erupted lavas and tephra range from trachybasaltic to trachybasaltic andesite, and crystal-hosted melt inclusions contain up to 3,000 ppm of sulphur by weight. The eruption was preceded by significant seismicity, detected by regional networks of sensors and accompanied by sustained tremor. Substantial infrasound was recorded at distances of hundreds to thousands of kilometres from the vent, beginning at the onset of the eruption and continuing for weeks. Analysis of ground deformation suggests the eruption was fed by a shallow, NW-SE-trending dike, which is consistent with field and satellite observations of vent distributions. Despite lack of prior planning and preparedness for volcanic events in the country, rapid coordination of the emergency response mitigated the human costs of the eruption.

Nature Communications, 2011

Rifting of the continents leading to plate rupture occurs by a combination of mechanical deformat... more Rifting of the continents leading to plate rupture occurs by a combination of mechanical deformation and magma intrusion, yet the spatial and temporal scales over which these alternate mechanisms localize extensional strain remain controversial. Here we quantify anisotropy of the upper crust across the volcanically active Afar Triple Junction using shear-wave splitting from local earthquakes to evaluate the distribution and orientation of strain in a region of continental breakup. The pattern of s-wave splitting in Afar is best explained by anisotropy from deformation-related structures, with the dramatic change in splitting parameters into the rift axis from the increased density of dyke-induced faulting combined with a contribution from oriented melt pockets near volcanic centres. The lack of rift-perpendicular anisotropy in the lithosphere, and corroborating geoscientific evidence of extension dominated by dyking, provide strong evidence that magma intrusion achieves the majority of plate opening in this zone of incipient plate rupture.