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| Titel |
The crustal viscosity gradient measured from post-seismic deformation: a case study of the 1997 Manyi (Tibet) earthquake |
| VerfasserIn |
T. Yamasaki, G. A. Houseman |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250062259
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| Zusammenfassung |
| The viscosity of the crust varies mainly with depth because of increasing temperature. We
attempt to measure that variation using the signature of post-seismic surface displacement
measured after the 1997 Manyi (Tibet) earthquake. Constraining that variation of viscosity is
important if we are to predict more accurately the evolution of stress in the crust during the
earthquake cycle. We previously used 3-D finite element calculations of the surface
displacement history following a strike-slip fault event, to show that the surface
displacements for a linear Maxwell visco-elastic model in which viscosity decreases
exponentially with depth (the DDV model) are closely similar to those for a uniform viscosity
(UNV) model, for a specific apparent (UNV) viscosity (ηu). The apparent viscosity that
best-fits the DDV model displacement decreases with distance from the fault, and the rate
of the change of ηu with distance from fault reflects the vertical gradient of the
viscosity. In the present study we apply that knowledge to the interpretation of an
InSAR dataset of the surface deformation in a three year period following the 1997
Manyi (Tibet) earthquake [Ryder et al., GJI, 169, 1009 - 10027, 2007] in order to
estimate the vertical viscosity gradient beneath the region. We analyse the rates of
displacement after an initial period (165 days) in which post-seismic slip is probably
significant. We infer a clear signature of the vertical viscosity gradient in the crust
based on the observed decrease of ηu with distance from the fault. We infer that the
1997 Manyi event occurs within an upper layer which is effectively elastic on the
time-scale of the inter-seismic period, ~ 420 - 850 yrs [van der Woerd et al., GRL, 27,
2353-2356, 2000], and the vertical viscosity gradient in the crust is consistent with
empirical power law creep measurements of the upper crustal materials. These
new constraints on the vertical viscosity gradient of the Tibetan crust advance the
knowledge of the crust and assist in better understanding of the earthquake cycle. |
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