HR: 0800h
AN: T51C-0690    [Abstracts]
TI: Surface Deformation During a Magmatic Intrusion: the Example of the Dabba'hu Rift Crisis of 2005-2006 (Afar, Ethiopia)
AU: * Grandin, R
EM: grandin@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, Laboratoire de Tectonique et Mecanique de la Lithosphere, Tour 24-14, 4, place Jussieu, Paris, 75252, France
AU: Socquet, A
AF: Institut de Physique du Globe de Paris, Laboratoire de Tectonique et Mecanique de la Lithosphere, Tour 24-14, 4, place Jussieu, Paris, 75252, France
AU: Binet, R
AF: Commisariat a l'Energie Atomique, Laboratoire de Detection et de Geophysique, BP 12, Bruyeres le Chatel, 91680, France
AU: Jacques, E
AF: Institut de Physique du Globe de Paris, Laboratoire de Tectonique et Mecanique de la Lithosphere, Tour 24-14, 4, place Jussieu, Paris, 75252, France
AU: Klinger, Y
AF: Institut de Physique du Globe de Paris, Laboratoire de Tectonique et Mecanique de la Lithosphere, Tour 24-14, 4, place Jussieu, Paris, 75252, France
AU: de Chabalier, J
AF: Institut de Physique du Globe de Paris, Laboratoire de Tectonique et Mecanique de la Lithosphere, Tour 24-14, 4, place Jussieu, Paris, 75252, France
AU: King, G
AF: Institut de Physique du Globe de Paris, Laboratoire de Tectonique et Mecanique de la Lithosphere, Tour 24-14, 4, place Jussieu, Paris, 75252, France
AU: Tait, S
AF: Institut de Physique du Globe de Paris, Laboratoire de Dynamique des Systemes Geologiques, Tour 24-14, 4, place Jussieu, Paris, 75252, France
AU: Tapponnier, P
AF: Institut de Physique du Globe de Paris, Laboratoire de Tectonique et Mecanique de la Lithosphere, Tour 24-14, 4, place Jussieu, Paris, 75252, France
AU: Delorme, A
AF: Institut de Physique du Globe de Paris, Laboratoire de Tectonique et Mecanique de la Lithosphere, Tour 24-14, 4, place Jussieu, Paris, 75252, France
AU: Elissalde, C
AF: Institut de Physique du Globe de Paris, Laboratoire de Tectonique et Mecanique de la Lithosphere, Tour 24-14, 4, place Jussieu, Paris, 75252, France
AB: In September 2005, a magmato-tectonic episode initiated in Western Afar (Ethiopia) when a swarm of moderate magnitude earthquakes (M<5.6) was recorded for several days. A small eruption also occurred on the eastern flank of Dabba'hu, a large silicic volcano located at the northern extremity of the Dabba'hu rift segment. The terrain is exceptionally favorable for InSAR imagery and surface fault mapping, making this event a rare opportunity to study how surface faulting and dike injection were mechanically coupled during the rifting event. Based on the combination of InSAR images shot on both ascending and descending tracks, and the correlation of SAR amplitude images, we deduced the vertical motions inside the rift during the main intrusion event. Together with the correlation of SPOT optical images, the horizontal component of opening can be retrieved. We provide evidence for an average of 6 m of opening across the 40 km northern Dabba'hu segment, during the September crisis. The inner floor of the rift subsided by ~ 2m, while the shoulders were uplifted by ~ 2m. A deficit of opening was observed in the southern segment during the main crisis. However, a second intrusive event occurred in mid-2006, leading to the further opening of this 20 km segment by an additional ~ 2m. A series of interferograms covering the post-crises periods show that significant motion also occurred between the crises and after the second crisis. Using a comparison between pre-crisis aerial photographs and post-crisis high-resolution Quickbird images, combined with SAR coherence images, we are able to map the structures that were reactivated during the crisis, and show extensive evidence of newly exposed fractures in recent basalts. The motion on a large number of en echelon faults and fissures could be observed with much greater detail than during the main rifting event. Using a DEM of the area, generated using SPOT images, the relation between faulting and rift morphology is addressed. Concentric subsidence and/or uplift occurred at various stages of the crisis on distinct volcanic edifices, pointing to a complex scenario for the possible connection between shallow and deep magmatic chambers. The estimated extension rate of 15 mm/year across the plate boundary [Vigny et al., 2006] yields a recurrence time of the order of 500 years for events of this magnitude. Surprisingly, despite the large volume of magma intruded during the September 2005 event (~ 15 km²), no basalt flows were observed.
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 8109 Continental tectonics: extensional (0905)
DE: 8485 Remote sensing of volcanoes
DE: 9305 Africa
SC: Tectonophysics [T]
MN: 2007 Fall Meeting