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| Titel |
Modeling the post-seismic deformations of the Aceh, Nias and Benkulu earthquakes |
| VerfasserIn |
Luce Fleitout, Jean-Didier Garaud, Georges Cailletaud, Christophe Vigny, Wim Simons, Boujewin Ambrosius, Itthi Trisirisatayawong, Chalermchon Satirapod |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250051355
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| Zusammenfassung |
| The giant seism of Aceh (december 2004) broke a large portion of the boundary between the
Indian ocean and the Sunda block. It was followed by the Nias and Bengkulu earthquakes.
For the first time in history, the deformations associated with a very large earthquake can be
followed by GPS, in particular by the SEAMERGE (far-field) and SUGAR (near-field) GPS
networks.
A 3D finite element code (Zebulon) is used to model both the cosismic and the
post-seismic deformations. The modeled zone is a large portion of spherical shell around
Sumatra, between 40Ë N and 20Ë S and from the Earth’s surface to the core-mantle boundary.
The mesh is refined close to the subduction zone.
We show that taking into account the lateral variations of the elastic properties in the
superficial layers (accretionary prism, continental crust...) is important for modeling the
coseismic deformation: it affects by more than 30% the ratio near-field over far-field of the
predicted surface displacements. The inverted cosismic displacements on the subduction
plane provide a very good fit to the GPS data for the three seisms.
The curves of post-seismic displacement, non-dimensionalized by the cosismic
displacement, present three very different patterns as function of time: For GPS stations
in the far-field, the total post-seismic displacement after 4 years is as large as the
cosismic displacement. The slope of the curves varies slowly. In the near-field, the
post-sismic displacement reaches only some 15% of the cosismic displacement and
it levels off after 2 years. In the middle-field (south-west coast of Sumatra), the
post-sismic displacement also levels-off with time but more slowly and it reaches more
than 30% of the cosismic displacement. We show that in order to fit these three
distinct displacement patterns, we need to invoke both viscoelastic deformation in the
asthenosphere and a low-viscosity wedge or sliding in the lower part of the subduction
plane.
The viscoelastic properties of the asthenosphere are rather precisely constrained: they are
consistent with a Maxwell rheology with a viscosity of the order of 5 1018Pas or a Burger
rheology with a long-term viscosity of 3 1019 Pa-s and a transient creep represented by a
Kelvin-Voigt element with a viscosity of 3 1018Pas and μKelvin = μelastic/3. The viscosities
of the low viscosity wedge or of the low-viscosity channel are of the order of 2.
1018Pas.
These large post-seismic deformations affect the deviatoric stresses in the whole
Sunda-block. They should also be considered in the interpretation of the intersismic signal. |
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