HR: 08:00h
AN: U21C-01 INVITED     [Abstracts]
TI: Coseismic Slip and Afterslip Associated to The Mw9.14 Aceh-Andaman Earthquake
AU: Chlieh, M
EM: chlieh@gps.caltech.edu
AF: Tectonic Observatory Project, California Institute of Technology, 1200 E. California Blvd. MC 100-23, Pasadena, CA 91125 United States
AU: * Avouac, J
EM: avouac@gps.caltech.edu
AF: Tectonic Observatory Project, California Institute of Technology, 1200 E. California Blvd. MC 100-23, Pasadena, CA 91125 United States
AU: Sieh, K
EM:
AF: Tectonic Observatory Project, California Institute of Technology, 1200 E. California Blvd. MC 100-23, Pasadena, CA 91125 United States
AU: Prawirodirdjo, L
EM:
AF: Tectonic Observatory Project, California Institute of Technology, 1200 E. California Blvd. MC 100-23, Pasadena, CA 91125 United States
AU: Bock, Y
EM:
AF: Tectonic Observatory Project, California Institute of Technology, 1200 E. California Blvd. MC 100-23, Pasadena, CA 91125 United States
AU: Hjorleifsdottir, V
EM:
AF: Tectonic Observatory Project, California Institute of Technology, 1200 E. California Blvd. MC 100-23, Pasadena, CA 91125 United States
AU: Ji, C
EM:
AF: Tectonic Observatory Project, California Institute of Technology, 1200 E. California Blvd. MC 100-23, Pasadena, CA 91125 United States
AU: Hebert, H
EM:
AF: Laboratoire de D‚tection et de G‚ophysique, CEA, BruyŠre-le-Chƒtel, 91680 France
AU: Sladen, A
EM:
AF: Laboratoire de D‚tection et de G‚ophysique, CEA, BruyŠre-le-Chƒtel, 91680 France
AU: Natawidjaja, D H
EM:
AF: Tectonic Observatory Project, California Institute of Technology, 1200 E. California Blvd. MC 100-23, Pasadena, CA 91125 United States
AU: Subarya, C
EM:
AF: Indonesia National Coordination Agency for Surveying and Mapping, Cibinong, Indonesia, 40135 Indonesia
AU: Galetzka, J
EM:
AF: Tectonic Observatory Project, California Institute of Technology, 1200 E. California Blvd. MC 100-23, Pasadena, CA 91125 United States
AB: The Sumatra-Andaman earthquake of December 26, 2004 is the first giant earthquake to occur since the advent of modern space-based geodesy and broadband seismology and therefore provides an unprecedented opportunity to investigate the characteristics of one of these most dreadful and rare events. We determine co-seismic and post-seismic deformation over the first month following the main shock using a variety of geodetic data. These include ground displacements from near-field Global Positioning System (GPS) surveys in northwestern Sumatra and in-situ paleogeodetic and remotely sensed observations of the vertical motion of coral reefs, campaign data and continuous GPS measurements from Thailand and Malaysia. The co-seismic model is mainly constrained from co-seismic displacement derived from daily solutions at 34 cGPS stations. It shows that earthquake ruptured the Sunda subduction megathrust over a distance of about 1300 km and a width of less than 150 km releasing a total moment of 6.7-7.0 10²2 Nm, (equivalent to Mw=9.15. This moment is slightly in excess of the 6.2 10²2 Nm moment released over the first 500s, as estimated from the inversion of seismic records. The latitudinal distribution of released moment derived from the two models compare remarkably well. This pattern is also found consistent with the 500s long source time function and rupture velocity derived from T waves recorded in the Indian Ocean. Finally, this co-seismic model is found consistent with the observed tsunami as measured from altimetric satellite measurements of the tsunami by JASON and TOPEX, as well as with the arrival times of the tsunami recorded by tide gage records at a number of sites bordering the Indian Ocean and Andaman Sea. We find no need for slow slip or delayed slip as proposed in some early studies. However, the geodetic data postdating the main shock by up to 40 days, require that slip must have continued on the plate interface after the 500s long seismic rupture. The corresponding additional geodetic moment is about 1.5 10²2 Nm, representing about 20 per cent of the co-seismic moment release. Comparison with the moment released by aftershocks, which amounts less than 1 per cent over the same period, shows that this deformation was mostly aseismic. Constraints on the depth distribution of afterslip are loose, but it seems that it must have occurred at depths less than about 50km, both updip and downdip of the seismically ruptured area. Time evolution of afterslip is consistent with rate-strengthening frictional afterslip. The proportion of aseismic slip is larger to the north, possibly due to the effect of the thick sediment cover entering the trench. These data shed some light on the physical parameters controlling the mode of slip along the plate interface. The ruptured area seems to coincide with the portion of the plate interface shallower than about 40km that was locked before the earthquake, as indicated from the previous background seismicity. From modelling the thermal structure of the plate interface we found that the position of the downdip end of the Locked fault Zone (LFZ) might be governed by temperature, with a transition to aseismic creep occurring around 300 to 350C, possibly controlled by the rheology of quartzo-feldspathic rocks dragged along the plate interface.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1209 Tectonic deformation (6924)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 1243 Space geodetic surveys
DE: 7240 Subduction zones (1207, 1219, 1240)
SC: Union [U]
MN: Fall Meeting 2005