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| Titel |
Use of interseismic GPS data: a novel way to evaluate the lithosphere rigidity variations. |
| VerfasserIn |
Severine Furst, Michel Peyret, Jean Chéry, Bijan Mohammadi |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250131737
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| Publikation (Nr.) |
 EGU/EGU2016-12175.pdf |
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| Zusammenfassung |
| Although the flexure of the lithosphere is well constrained using a simple secular cooling
model in the ocean (Stewart and Watts, 1997), this mechanical parameter is not obvious to
determine in the continents. One commonly estimates the flexural rigidity, expressed through
the effective elastic thickness (Te) of the lithosphere, by studying the lithosphere’s vertical
motion induced by long-term geological loads. Here, we suggest a similar approach,
using the horizontal velocities to evaluate lateral rigidity variations. To illustrate our
method, we select the Western United States zone, where areas with high rigidity
(Sierra Nevada) are connected with others displaying low rigidities (San Andreas
Fault).
Our technique is based on an inversion problem, aiming to infer the effective rigidity from
interseismic strain distribution measured by geodetic methods. The forward problem is
defined using the equations of linear elasticity in a plane stress finite element code. This
method involves the minimisation of a cost function defined as the quadratic measure of the
differences between measured and modeled velocity fields on a discrete set of points.
Gradient of the functional, with respect to the independent parameters of the model, is
computed using an adjoint formulation. Thanks to this construction, the mapping of
the rigidity can be fulfilled with a large number of parameters. The optimisation
chart is validated first on synthetic velocity data sets corresponding to the surface
motion of a screw dislocation with different locking depths. Then, the effective
rigidity variations of the Western United States are estimated using a dense geodetic
network.
The inversion displays low effective rigidities along the San Andreas Fault and in the
Eastern California Shear zone, while rigid areas are found in the Sierra Nevada and in the
South Basin and Range. High rigidity values are strongly correlated with regions presenting
small deformations and vice-versa. In addition to these results, we develop an approach built
on the new theory about extreme scenarios to evaluate the reliability of our inversion.
To do so, we consider parameters uncertainties linked to the propagation of the
data error through the optimisation procedure. With this uncertainties map, we join
an estimation of the confidence to the computed rigidity distribution. Finally, we
compare the rigidity variations and deformation to the results from the literature. |
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