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Evidence for postseismic deformation of the lower crust following the 2004 Mw6.0 Parkfield earthquake

Summary: Evidence for postseismic deformation of the lower
crust following the 2004 Mw6.0 Parkfield earthquake
Lucile Bruhat,1,2
Sylvain Barbot,1
and JeanPhilippe Avouac1
Received 2 November 2010; revised 22 February 2011; accepted 4 May 2011; published 5 August 2011.
[1] Previous studies have shown that postseismic relaxation following the 2004 Mw6.0
Parkfield, CA, earthquake is dominated by afterslip. However, we show that some fraction
of the afterslip inferred from kinematic inversion to have occurred immediately below
the seismically ruptured area may in fact be a substitute for viscous postseismic
deformation of the lower crust. Using continuous GPS and synthetic aperture radar
interferometry, we estimate the relative contribution of shallow afterslip (at depth less than
20km) and deeper seated deformation required to account for observed postseismic surface
displacements. Exploiting the possible separation in space and time of the time series
of displacements predicted from viscoelastic relaxation, we devise a linear inversion
scheme that allows inverting jointly for the contribution of afterslip and viscoelastic flow
as a function of time. We find that a wide range of models involving variable amounts of
viscoelastic deformation can fit the observations equally well provided that they allow
some fraction of deepseated deformation (at depth larger than 20 km). These models
require that the moment released by postseismic relaxation over 5 years following the


Source: Avouac, Jean-Philippe - Division of Geological and Planetary Sciences, California Institute of Technology


Collections: Geosciences