HR: 14:25h
AN: G13C-04    [Abstracts]
TI: Micro-deformation and Micro-seismicity in the Mak'arrasou Fault Zone in Afar, Kinematics Implications
AU: * Peltzer, G
EM: peltzer@ess.ucla.edu
AF: Earth and Space Department, UCLA, 595 Charles Young Drive East, Los Angeles, CA 90095, United States
AU: * Peltzer, G
EM: peltzer@ess.ucla.edu
AF: Jet propulsion Laboratory, Caltech, 4800 Oak Grove Drive, Pasadena, CA 91109, United States
AU: Doubre, C
EM: cdoubre@eost.u-strasbg.fr
AF: IPGS-EOST, 5, rue René Descartes, Strasbourg, 67084, France
AU: Tomic, J
EM: tomic@moho.ess.ucla.edu
AF: Earth and Space Department, UCLA, 595 Charles Young Drive East, Los Angeles, CA 90095, United States
AB: The Mak'arrasou fault zone is formed of a multitude of N135-150°E-striking, right-stepping normal faults transferring the extension from the Asal Rift in the south to the Manda Inakir Rift, ~70 km to the north. Its overall NS direction and the regional extension in the N40°E direction (estimated by GPS) between the Arabia plate and the central part of the Afar depression, make the Mak'arrasou fault zone a left-lateral transfer zone. The seismicity is low in the south of the zone and inexistent or unknown in its northern part. We use the 10- year archive of RADARSAT InSAR data acquired from ascending and descending passes of the satellite to map two components of the surface velocity between 1997 and 2007. Beside the far-field movement across the Mak'arrasou fault zone, the most notable features of the deformation field during the 10-year period are localized areas of subsidence in the hanging wall of a normal fault in the southern part of the zone. The radar data analysis in time series shows that the largest subsidence of ~20mm occurred during two periods of slip on the fault in July and September 2001. The periods of ground movement correspond to swarms of small earthquakes in the vicinity of the fault, releasing a total moment of 8.75 10¹³ Nm over 45 days. We invert the integrated line of sight displacement fields from two stacks of 25 ascending and descending interferograms spanning the 3- month period to solve for the slip components on a small fault patch oriented N25°W, parallel to the local fault strike, and dipping 60° to the NE. The derived source mechanism is ~31 mm of slip with a rake of 82° from north, yielding a geodetic moment of 4.6 10¹⁵ Nm and consistent with a N46°E direction of extension. This direction is only ~6° east of the regional N40°E direction of extension, suggesting that the Mak'arrasou faults are accommodating the regional strain field with minor, if any, counter- clockwise rotation of the intervening blocks. This result is consistent with the absence of long-term rotation estimated using paleomagnetic observations in 1.8±0.4 Ma lava rocks in the southern part of the Mak'arrasou fault zone (Manighetti et al., 2001).
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
DE: 8109 Continental tectonics: extensional (0905)
DE: 8194 Instruments and techniques
SC: Geodesy [G]
MN: 2007 Fall Meeting