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Journal: |
Earth and Planetary Science Letters 2018 No.495
clicks:263 |
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Title:
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Author:
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Faqi Diao, et al. |
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Adress: |
Institute of Geophysics and Geomatics, China University of Geosciences, Wuhan 430074, China |
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Abstract:
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Long-term and wide-area geodetic observations may allow identifying distinct postseismic deformation processes following large earthquakes, and thus can reveal fault behavior and permit quantifying complexities in lithospheric rheology. In this paper, the first 7 years of GPS (Global Positioning System) displacement data following the 2008 Mw7.9 Wenchuan earthquake are used to study the relevant mechanisms of postseismic deformation. Two simple models that consider either afterslip or viscoelastic relaxation as the unitary mechanism of the postseismic deformation are tested at first. After analyzing the limitations and complementarity of these two separated models, a combined model incorporating the two main mechanisms is presented. In contrast to previous studies, which mostly assume that afterslip and viscoelastic relaxation are independent, our combined model includes the secondary viscoelastic relaxation effect induced by transient afterslip. Modeling results suggest that the middle- to far-field postseismic deformation is mainly induced by viscoelastic relaxation of the coseismic stress change in the lower crust, whereas the near-field displacement is dominantly caused by stress-driven aseismic afterslip. The seismic moment released by the transient afterslip corresponds to an Mw7.4 earthquake, or 25% of that released by the Mw7.9 main shock. With a characteristic decay time of 1.2 yr, most afterslip (∼80%) is released in the first 2 years. Negligible aseismic afterslip is observed in the seismic gap between the Wenchuan and Lushan earthquakes, indicating the locked state of the fault within this segment. The effective lower crustal viscosity of the eastern Tibetan Plateau is estimated to be 2.0×1018Pas
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