SCEC Award Number 12056 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Numerical models of stress transfer from plate motion to mature transform faults
Name Organization
Yuri Fialko University of California, San Diego
Other Participants Graduate student Chris Takeuchi
SCEC Priorities 1b, 1d, 4e SCEC Groups SDOT
Report Due Date 03/15/2013 Date Report Submitted N/A
Project Abstract
We have extended 2-D anti-plane strain models of Takeuchi and Fialko (2012) 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.
Intellectual Merit We use numerical models that incorporate realistic geotherms, far-field loading
rates and loading histories, depth-dependent compositions, and
constitutive relationships inferred from laboratory experiments, to investigate conditions under which permanent shear
zones may develop in an initially unstrained ductile substrate. This will allow us to evaluate the magnitude and distribution of deviatoric stresses in
the ductile lower crust and upper mantle, and make inferences about
the long-term strength of continental lithosphere as a function of
temperature regime, composition, deformation rate, total displacement,
and other relevant factors.
Broader Impacts This project provided training and support for one graduate student
and one postdoc. The PI (Fialko) used results of this study in a
graduate class taught at SIO.
Exemplary Figure Figure 1.