Project Abstract
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We have extended our 2-D anti-plane strain models to three dimensions to investigate effects of viscous shear zones that result from thermomechanical
coupling on the geodetically observable deformation transients
following an earthquake on a vertical strike-slip fault. We also
explored potential kinematic similarities between viscoelastic models
incorporating shear zones, and elastic models incorporating
rate-strengthening friction on a deep aseismic fault root. We find
that the thermally-activated shear zones have little effect on
postseismic relaxation. In particular, the presence of shear zones
does not change the polarity of vertical displacements in cases of
rheologies that are able to generate robust postseismic transients.
Stronger rheologies can give rise to an opposite polarity of vertical
displacements, but the amplitude of the predicted transient
deformation is generally negligible. We conclude that additional (to
thermomechanical coupling) mechanisms of strain localization are
required for a viscoelastic model to produce a vertical deformation
pattern similar to that due to afterslip on a deep extension of a
fault. We also investigated the discriminating power of models
incorporating Burgers and power law rheology. These rheologies were
proposed to explain postseismic transients following large (M7)
earthquakes in the Mojave desert, Eastern California. Numerical
simulations indicate that it may be difficult to distinguish between
these rheologies even with high-quality geodetic observations for
observation periods less than a decade. Longer observations, however,
may potentially allow discrimination between the competing models, as
illustrated by the model comparisons with available GPS and InSAR
data. |
