Capturing magma intrusion and faulting processes during continental rupture: seismicity of the Dabbahu (Afar) rift
Capturing magma intrusion and faulting processes during continental rupture: seismicity of the Dabbahu (Afar) rift
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 (<2 km) above a shadow zone, interpreted as a magma chamber between 2.5 and 6 km subsurface. InSAR and continuous GPS data show uplift above a shallow source in zone (2) and uplift above the largely aseismic Gab'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.
seismic cycle, seismicity and tectonics, volcano seismology, neotectonics, africa
1138-1152
Ebinger, C.J.
aedfe44b-76f6-4882-9522-0079fba9feda
Keir, D.
5616f81f-bf1b-4678-a167-3160b5647c65
Ayele, A.
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Calais, E.
91f92d1c-75fa-4521-a69e-92b6b4316851
Wright, T.J.
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Belachew, M.
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Hammond, J.O.S.
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Campbell, E.
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Buck, W.R.
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2008
Ebinger, C.J.
aedfe44b-76f6-4882-9522-0079fba9feda
Keir, D.
5616f81f-bf1b-4678-a167-3160b5647c65
Ayele, A.
2a0d90e9-a4be-4484-9301-5c4df46f9407
Calais, E.
91f92d1c-75fa-4521-a69e-92b6b4316851
Wright, T.J.
aeda4400-2cf2-4875-aade-b1c53f4f4fb7
Belachew, M.
3a0232fd-0c1b-49ad-82a8-9e5aaf1e3cfa
Hammond, J.O.S.
df081c77-2e69-4753-8846-549826d905bb
Campbell, E.
5b986b1f-2d49-4fde-a80e-dbee4e1e3441
Buck, W.R.
c8c91b1e-3b4d-4224-a79e-f0fdae02db1e
Ebinger, C.J., Keir, D., Ayele, A., Calais, E., Wright, T.J., Belachew, M., Hammond, J.O.S., Campbell, E. and Buck, W.R.
(2008)
Capturing magma intrusion and faulting processes during continental rupture: seismicity of the Dabbahu (Afar) rift.
Geophysical Journal International, 174 (3), .
(doi:10.1111/j.1365-246X.2008.03877.x).
Abstract
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 (<2 km) above a shadow zone, interpreted as a magma chamber between 2.5 and 6 km subsurface. InSAR and continuous GPS data show uplift above a shallow source in zone (2) and uplift above the largely aseismic Gab'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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Published date: 2008
Keywords:
seismic cycle, seismicity and tectonics, volcano seismology, neotectonics, africa
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Local EPrints ID: 175153
URI: http://eprints.soton.ac.uk/id/eprint/175153
ISSN: 0956-540X
PURE UUID: d4094d8b-ae4b-43aa-b37e-f445908595ea
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Date deposited: 22 Feb 2011 16:29
Last modified: 14 Mar 2024 02:57
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Contributors
Author:
C.J. Ebinger
Author:
A. Ayele
Author:
E. Calais
Author:
T.J. Wright
Author:
M. Belachew
Author:
J.O.S. Hammond
Author:
E. Campbell
Author:
W.R. Buck
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