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Science 30 June 2006:
Vol. 312. no. 5782, pp. 1921 - 1926
DOI: 10.1126/science.1126960
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Research Articles

Frictional Afterslip Following the 2005 Nias-Simeulue Earthquake, Sumatra

Ya-Ju Hsu,1* Mark Simons,1 Jean-Philippe Avouac,1 John Galetzka,1 Kerry Sieh,1 Mohamed Chlieh,1 Danny Natawidjaja,2 Linette Prawirodirdjo,3 Yehuda Bock3

Continuously recording Global Positioning System stations near the 28 March 2005 rupture of the Sunda megathrust [moment magnitude (Mw) 8.7] show that the earthquake triggered aseismic frictional afterslip on the subduction megathrust, with a major fraction of this slip in the up-dip direction from the main rupture. Eleven months after the main shock, afterslip continues at rates several times the average interseismic rate, resulting in deformation equivalent to at least a Mw 8.2 earthquake. In general, along-strike variations in frictional behavior appear to persist over multiple earthquake cycles. Aftershocks cluster along the boundary between the region of coseismic slip and the up-dip creeping zone. We observe that the cumulative number of aftershocks increases linearly with postseismic displacements; this finding suggests that the temporal evolution of aftershocks is governed by afterslip.

1 Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA.
2 Research Center for Geotechnology, Indonesian Institute of Sciences, Bandung 40135, Indonesia.
3 Institute of Geophysics and Planetary Physics, University of California, San Diego, La Jolla, CA 92093, USA.

* To whom correspondence should be addressed. E-mail: yaru{at}gps.caltech.edu

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
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Rupture Kinematics of the 2005 Mw 8.6 Nias-Simeulue Earthquake from the Joint Inversion of Seismic and Geodetic Data.
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