HR: 08:45h
AN: T31F-04 INVITED    [Abstracts]
TI: Capturing Magma Intrusion and Faulting Processes During Continental Rupture: Seismicity of the Dabbahu (Afar) rift
AU: * Ebinger, C J
EM: ebinger@earth.rochester.edu
AF: Earth & Environmental Sciences, University of Rochester, Rochester, 14618,
AU: Keir, D B
EM: d.keir@gl.rhul.ac.uk
AF: Earth Sciences, University of Leeds, Leeds, LS29JT, United Kingdom
AU: Ayele, A
EM: atalay@geobs.aau.edu.et
AF: Geophysical Observatory Addis Ababa University, PO Box 2302, Addis Ababa, 00ETH, Ethiopia
AU: Campbell, E
EM: ecampbell@earth.rochester.edu
AF: Earth & Environmental Sciences, University of Rochester, Rochester, 14618,
AU: Belachew, M
EM: manahloh@yahoo.com
AF: Geophysical Observatory Addis Ababa University, PO Box 2302, Addis Ababa, 00ETH, Ethiopia
AU: Hammond, J
EM: J.Hammond@bristol.ac.uk
AF: Earth Sciences, University of Bristol, Bristol, BS81RJ, United Kingdom
AU: Wright, T
EM: t.wright@see.leeds.ac.uk
AF: Earth Sciences, University of Leeds, Leeds, LS29JT, United Kingdom
AU: Calais, E
EM: ecalais@purdue.edu
AF: Earth, Atmospheric Sciences, Purdue University, W Lafayette, 47907,
AB: Continental rupture models emphasize the role of faults in extensional strain accommodation; magma intrusion is commonly overlooked. The volcanically and seismically active Afar depression of Ethiopia is a broad zone of extensional strain encompassing zones of incipient plate rupture. One of these highly extended rift segments entered a phase of active rifting in September, 2005. Earthquakes recorded on a temporary seismic array October 05 - April 06, 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. The depth distribution of microseismicity indicates that the dyke rises from ~15 km to <3 km from the surface along the ~60 km-long length of the tectono-magmatic segment. Focal mechanisms show rift- normal opening. The seismicity, InSAR and structural patterns all suggest that magma injection continued at least 3 months after the main episode; the mid-crustal level of the seismogenic zone suggests the deep roots of the dike may have remained open during this time. Persistent seismic swarms at 2 sites on Dabbahu volcano coincide with areas of deformation identified in the processed InSAR data: (1) a northwestward-dipping zone of seismicity interpreted as a listric fault that soles out at 8 km coincides with a broad zone of subsidence, and (2) a more diffuse, 8 km-radius zone of shallow seismicity (<2 km), a shadow zone between 2.5 and 6 km, and a narrow ‘tube' of events between 14 and 6 km. InSAR data show uplift above a shallow source in zone (2). The patterns of seismicity provide a 3D perspective of magma feeding systems maintaining the along-axis segmentation of this incipient seafloor spreading segment surrounded by transitional continental crust.
DE: 8002 Continental neotectonics (8107)
DE: 8178 Tectonics and magmatism
SC: Tectonophysics [T]
MN: 2007 Fall Meeting