3 results for Ayele, A

  • Capturing magma intrusion and faulting processes during continental rupture: seismicity of the Dabbahu (Afar) rift

    Ebinger, CJ; Keir, D; Ayele, A; Calais, E; Wright, TJ; Belachew, M; Hammond, JOS; Campbell, Melanie; Buck, WR (2008)

    Journal article
    The University of Auckland Library

    Continental rupture models emphasize the role of faults in extensional strain accommodation; extension by dyke intrusion is commonly overlooked. A major rifting episode that began in 2005 September in the Afar depression of Ethiopia provides an opportunity to examine strain accommodation in a zone of incipient plate rupture. Earthquakes recorded on a temporary seismic array (2005 October to 2006 April), direct observation of fault patterns and geodetic data document ongoing strain and continued dyke intrusion along the ∼60-km long Dabbahu rift segment defined in earlier remote sensing studies. Epicentral locations lie along a ∼3 km wide, ∼50 km long swath that curves into the SE flank of Dabbahu volcano; a second strand continues to the north toward Gab'ho volcano. Considering the ∼8 m of opening in the September crisis, we interpret the depth distribution of microseismicity as the dyke intrusion zone; the dykes rise from ∼10 km to the near-surface along the ∼60-km long length of the tectono-magmatic segment. Focal mechanisms indicate slip along NNW-striking normal faults, perpendicular to the Arabia–Nubia plate opening vector. The seismicity, InSAR, continuous GPS and structural patterns all suggest that magma injection from lower or subcrustal magma reservoirs continued at least 3 months after the main episode. Persistent earthquake swarms at two sites on Dabbahu volcano coincide with areas of deformation identified in the InSAR data: (1) an elliptical, northwestward-dipping zone of seismicity and subsidence interpreted as a magma conduit, and (2) a more diffuse, 8-km radius zone of shallow seismicity (ho volcano. The patterns of seismicity provide a 3-D perspective of magma feeding systems maintaining the along-axis segmentation of this incipient seafloor spreading segment.

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  • Comparison of dike intrusions in an incipient seafloor-spreading segment in Afar, Ethiopia: Seismicity perspectives

    Belachew, M; Ebinger, C; Cote, D; Keir, D; Rowland, Julie; Hammond, JOS; Ayele, A (2011-06)

    Journal article
    The University of Auckland Library

    Oceanic crust is accreted through the emplacement of dikes at spreading ridges, but the role of dike intrusion in plate boundary deformation during continental rupture remains poorly understood. Between 2005 and 2009 the ∼70 km long Dabbahu‐Manda Hararo rift segment in Ethiopia has experienced 14 large volume dike intrusions, 9 of which were recorded on temporary seismic arrays. A detailed comparison of the seismic characteristics of the seismically monitored dikes is presented with implications for dike intrusion processes and magmatic plumbing systems. All of the migrating swarms of earthquakes started from a 80% of energy is released during the propagation phase, with minimal seismic energy release after the dike propagation ceases. We interpret that faulting and graben formation above the dikes occurs hours after the passage of the dike tip, coincident with the onset of low‐frequency earthquakes. Dike lengths show no systematic reduction in length with time, suggesting that topographic loading and stress barriers influence dike length, as well as changes in tectonic stress. The propagation velocities of all the dikes follow a decaying exponential. Northward propagating dikes had faster average velocities than those that propagated southward, suggesting preconditioning by the 2005 megadike, or ongoing heating from a subcrustal magma source north of the midsegment.

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  • Length and Timescales of Rift Faulting and Magma Intrusion: The Afar Rifting Cycle from 2005 to Present

    Ebinger, C; Ayele, A; Keir, D; Rowland, Julie; Yirgu, G; Wright, T; Belachew, M; Hamling, I (2010)

    Journal article
    The University of Auckland Library

    Although fault and magmatic processes have achieved plate spreading at mid-ocean ridges throughout Earth’s history, discrete rifting episodes have rarely been observed. This paper synthesizes ongoing seismic, structural, space-based geodetic, and petrologic studies from the subaerial Red Sea rift in Ethiopia where a major rifting episode commenced in September 2005. Our aims are to determine the length and timescales of magmatism and faulting, the partitioning of strain between faulting and magmatism, and their implications for the maintenance of along-axis segmentation. Most of the magma for the initial and subsequent 12 intrusions was sourced from the center of the Dabbahu-Manda Hararo rift segment. Strain is accommodated primarily by axial dike intrusions fed from mid-segment magma chamber(s). These findings show that episodic (approximate century interval), rapid opening of discrete rift segments is the primary mechanism of plate boundary deformation. The scale (∼65 km × 8 km) and intensity of crustal deformation (∼6 m), as well as the volume of intrusive and extrusive magmatism (>3 km3), provokes a re-evaluation of seismic and volcanic hazards in subaerial rift zones.

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