Studying the viscosity of lower crust of Qinghai-Tibet Plateau according to post-seismic deformation |
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| Authors: | ChaoJun Zhang JianLing Cao YaoLin Shi |
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| Institution: | (1) China Earthquake Network Center, Beijing, 100045, China;(2) Laboratory of Computational Geodynamics, Graduate University of the Chinese Academy of Sciences, Beijing, 100049, China |
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| Abstract: | The viscosity of lower crust of Qinghai-Tibet Plateau on earth should be determined. It has become a predominant problem in
quantitative research on geodynamics. Its order of magnitude will have a great influence on the results of quantitative modeling.
To obtain the viscosity of lower crust of Qinghai-Tibet Plateau, this parameter was calculated by three methods. The first
is based on the estimation on the temperature state of Qinghai-Tibet Plateau in the deep part, and the viscosity of lower
crust of northern Plateau was recomputed with strain rate derived from rheology law and GPS observation. Effective viscosity
of middle crust in Kunlun region is between 1020 and 1022 Pa·s, and that of lower crust is between 1019 and 1021 Pa·s; the second is based on three kinds of rheological models used to fit the post-seismic deformation recorded by cross-over
fault GPS sites set after M
s8.1 Kunlun earthquake in 2001. The viscosity of lower crust obtained by this method is of 1017 Pa·s order of magnitude. However, higher viscosity is required to fit the data of south fault better, and the lower one is
required to fit the data of north fault better. The viscosity of lower crust, which was obtained by fitting the cross-over
fault post-seismic deformation after M
s7.6 Luhuo earthquake in 1973, is of 1019 Pa·s order of magnitude. Non-linear relationship between effective viscosity and strain rate is ignored in the former research
of effective viscosity. This research shows the difference of effective viscosity obtained from laboratory experiment, and
shorter and longer time post-seismic deformation after large earthquakes can be explained in phase.
Supported by National Basic Research Program of China (Grant No. 2004CB418405), National Natural Science Foundation of China
(Grant No. 40774048), Important Direction Item of Knowledge Innovation Project of Chinese Academy of Sciences (Grant No. KZCX2-YW-123)
and Basic Scientific Research Project of Earthquake (Grant No. 02076902-05) |
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| Keywords: | rheological model strain rate rheological law post-seismic deformation viscosity |
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