Constraining melt geometries beneath the Afar Depression, Ethiopia from teleseismic receiver functions: The anisotropic H‐<b>κ</b>stacking technique

Hammond, James

doi:10.1002/2013gc005186

Cited by 62 publications

(88 citation statements)

References 66 publications

(100 reference statements)

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“…We compare to the Vs structure of the southeastern plateau, least modified by rifting. We estimate ~3% melt for the MER, within the range of ~0.5–5% from previous seismic studies (Gallacher et al, ; Guidarelli et al, ; Hammond, ). However, models from magnetotelluric and gravity studies yield higher melt fractions of 3–20% (Cornwell et al, ; Keranen et al, ; Whaler & Hautot, ).…”

Section: Discussionsupporting

confidence: 70%

Using Ambient Noise to Image the Northern East African Rift

Chambers

Harmon

Keir

et al. 2019

Geochem Geophys Geosyst

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The northern East African Rift (EAR) is a unique location where we observe continental rifting in the Main Ethiopian Rift (MER) transitioning to incipient seafloor spreading in Afar. Here we present a 3‐D absolute shear wave velocity model of the crust and uppermost mantle of the northern EAR generated from ambient noise tomography. We generate 4,820 station pair correlation functions, from 170 stations (present over 12 years), which were inverted for phase velocity from 8–33 s period and finally for 3‐D absolute shear velocity structure to 60‐km depth. Everywhere in the uppermost mantle, shear velocity is slower than expected for a mantle peridotite composition (<4.1 km/s). This suggests the presence of pervasive partial melt, with focused upwelling and melt storage beneath the MER, where the slowest velocities (3.20 km/s ± 0.03) are observed. Average crustal shear velocity is faster beneath Afar (3.83 km/s ± 0.04) than the MER (3.60 km/s ± 0.04), albeit Afar has localized slow velocities beneath active volcanic centers. We interpret these slow‐velocity regions (including the MER) as magmatic intrusions and heating of the crust. Beneath the northwestern plateau, crustal velocities are laterally heterogeneous (3.3–3.65 ± 0.05 km/s at 10 km), suggesting a complex geological history and inhomogeneous magma distribution during rift development. Comparison between the MER and Afar allows us to draw conclusions between different stages of rifting. In particular, the MER has the slowest crustal velocities, consistent with longer magma residence times in the crust, early during the breakup process.

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Section: Discussionsupporting

confidence: 70%

Using Ambient Noise to Image the Northern East African Rift

Chambers

Harmon

Keir

et al. 2019

Geochem Geophys Geosyst

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“…With water expected to alter the depth of the 520, it is plausible that the variability in depth is also related to water content [Inoue et al, 2010]. A recent study of the 520 beneath the African continent, incorporating data from station ATD, also attests to the variability of this discontinuity beneath our study region [Juli a and Nyblade, 2013].…”

Section: Discussionmentioning

confidence: 59%

Hydrous upwelling across the mantle transition zone beneath the Afar Triple Junction

Thompson

Hammond

Kendall

et al. 2015

Geochem. Geophys. Geosyst.

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The mechanisms that drive the upwelling of chemical heterogeneity from the lower to upper mantle (e.g., thermal versus compositional buoyancy) are key to our understanding of whole mantle convective processes. We address these issues through a receiver function study on new seismic data from recent deployments located on the Afar Triple Junction, a location associated with deep mantle upwelling. The detailed images of upper mantle and mantle transition zone structure illuminate features that give insights into the nature of upwelling from the deep Earth. A seismic low-velocity layer directly above the mantle transition zone, interpreted as a stable melt layer, along with a prominent 520 km discontinuity suggest the presence of a hydrous upwelling. A relatively uniform transition zone thickness across the region suggests a weak thermal anomaly (<100 K) may be present and that upwelling must be at least partly driven by compositional buoyancy. The results suggest that the lower mantle is a source of volatile rich, chemically distinct upwellings that influence the structure of the upper mantle, and potentially the chemistry of surface lavas.

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“…There is extensive evidence, from Interferometric Synthetic Aperture Radar, magnetics, receiver functions, magnetotellurics, and seismic anisotropy for the presence of dikes and sills in the crust south of 13°N in Afar (Wright et al, 2006;Keir et al, 2011;Bridges et al, 2012;Desissa et al, 2013;Hammond, 2014). Furthermore, a study into 40 years of seismicity in Afar by Hofstetter and Beyth (2003) found that > 50% of the geodetic moment, as predicted by plate separation rates, is taken up aseismically.…”

Section: Geological Settingmentioning

confidence: 99%

Local Earthquake Magnitude Scale andb‐Value for the Danakil Region of Northern Afar

Illsley‐Kemp¹,

Keir²,

Bull³

et al. 2017

Bulletin of the Seismological Society of America

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The Danakil region of northern Afar is an area of ongoing seismic and volcanic activity caused by the final stages of continental breakup. To improve the quantification of seismicity, we developed a calibrated local earthquake magnitude scale. The accurate calculation of earthquake magnitudes allows the estimation of b-values and maximum magnitudes, both of which are essential for seismic-hazard analysis. Earthquake data collected between February 2011 and February 2013 on 11 three-component broadband seismometers were analyzed. A total of 4275 earthquakes were recorded over hypocentral distances ranging from 0 to 400 km. A total of 32,904 zero-to-peak amplitude measurements (A) were measured on the seismometer's horizontal components and were incorporated into a direct linear inversion that solved for all individual local earthquake magnitudes (M L ), 22 station correction factors (C), and 2 distance-dependent factors (n, K) in the equation M L logA− logA 0 C. The resultant distance correction term is given by − logA 0 1:274336 logr=17 − 0:000273r − 17 2. This distance correction term suggests that attenuation in the upper and mid-crust of northern Afar is relatively high, consistent with the presence of magmatic intrusions and partial melt. In contrast, attenuation in the lower crust and uppermost mantle is anomalously low, interpreted to be caused by a high melt fraction causing attenuation to occur outside the seismic frequency band. The calculated station corrections serve to reduce the M L residuals significantly but do not show a correlation with regional geology. The cumulative seismicity rate produces a b-value of 0:9 0:06, which is higher than most regions of continental rifting yet lower than values recorded at midocean ridges, further supporting the hypothesis that northern Afar is transitioning to seafloor spreading.Electronic Supplement: List of all local earthquakes used in the study with calculated local magnitudes and associated magnitude error.

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Constraining melt geometries beneath the Afar Depression, Ethiopia from teleseismic receiver functions: The anisotropic H‐κstacking technique

Cited by 62 publications

References 66 publications

Using Ambient Noise to Image the Northern East African Rift

Using Ambient Noise to Image the Northern East African Rift

Hydrous upwelling across the mantle transition zone beneath the Afar Triple Junction

Local Earthquake Magnitude Scale andb‐Value for the Danakil Region of Northern Afar

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