HR: 11:05h
AN: G42A-04    [Abstracts]
TI: Eight Years of Surface Deformation in the Asal-Ghoubbet Rift (Afar Depression) Observed With SAR Data
AU: * Doubre, C
EM: cdoubre@ess.ucla.edu
AF: Department of Earth & Space Sciences, UCLA, Geology Building 595 Charles E. Young Drive East, Los Angeles, CA 90095-1567 United States
AU: Peltzer, G
EM: gilles@altyn.ess.ucla.edu
AF: Department of Earth & Space Sciences, UCLA, Geology Building 595 Charles E. Young Drive East, Los Angeles, CA 90095-1567 United States
AU: Peltzer, G
EM: gilles@altyn.ess.ucla.edu
AF: Jet Propulsion Laboratory, California Institute of Technology 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AU: Manighetti, I
EM: imanighe@obs.ujf-grenoble.fr
AF: Laboratoire de G‚ophysique Interne et Tectonophysique (LGIT), BP 53, Grenoble Cedex 9, 38041 France
AU: Jacques, E
EM: jacques@ipgp.jussieu.fr
AF: Institut de Physique du Globe, 5, rue Ren‚ Descartes, Strasbourg, 67084 France
AB: The volcano-tectonic Asal-Ghoubbet rift (Djibouti) is the youngest spreading segment of the Aden oceanic ridge propagating inland into the Afar Depression. The deformation in the rift is characterized by magmatic inflation and dilatation (dyking), distributed extension, fissure opening, and normal faulting, contributing to a far field opening velocity of ~1.5 cm/yr. We use radar interferometry data acquired by the Canadian satellite Radarsat on 24-day repeat, descending passes to measure the surface deformation in a 100 km wide region centered on the rift. The data set defines 87 epochs of acquisitions distributed between 1997 and 2005. We combined the SAR data into 354 full-resolution interferograms and solved for incremental displacements between epochs using a least-square approach [Berardino et al., 2002]. The resulting line of sight displacement map time series shows the following features: - A 40 km-wide zone centered on the rift is uplifted as a dome at a steady rate. - The central rift is subsiding with respect to the north and south shoulders. The velocity field shows a marked asymmetry with faster rates occurring along the northern edge of the rift. The mean velocity of the relative movement of the subsiding inner floor with respect to the northern up-lifting shoulder reaches 7 mm/yr. - Subsidence is faster in the north half of the inner floor of the rift and is associated with episodic creep events on normal faults. These includes a slip of 16 mm on the north-dipping δ fault in 2003 and an episode of accelerated creep of 10 mm occurring in 2000 on the γ fault, which is creeping at a steady rate of 3.5 mm/yr. A northern-dipping normal fault is slipping with a mean rate of 1.4 mm/yr and accommodates also the subsidence of the northern part of the inner floor. Unlike other active faults, this one does not coincide with a topographic scarp but shows evidence of surface creep in the velocity field. - The southeastern part of F fault system is the only fault clearly active on the south side of the rift axis and shows a creep event of 9 mm in 2002. We investigate the spatial and temporal relationship between deformation events observed in the SAR data and the catalog of seismicity collected by the Djibouti Observatory and during field campaign in the winter 2000/2001. We observe that creep events are generally associated with bursts of micro-seismicity distributed in the vicinity of the fault, or with swarms of small events concentrated below the fault. These observations suggest that while the overall region is deforming in response to the steady inflation of a magmatic chamber below the central rift, the faults and dykes that accommodate the deformation at the surface are sensitive and respond rapidly to small stress changes occurring episodically within the rift.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 6924 Interferometry (1207, 1209, 1242)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8004 Dynamics and mechanics of faulting (8118)
DE: 8178 Tectonics and magmatism
SC: Geodesy [G]
MN: Fall Meeting 2005