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Viscoelastic Relaxation and Afterslip Inferred From a Decade of Geodetic Measurements After the 2001 Mw7.8 Kokoxili, China Earthquake

Session: Modern Geodesy for Observation and Its Modeling of Earthquake Deformation

Type: Oral

Date: 4/19/2021

Presentation Time: 05:00 PM Pacific

Description: 

The Mw 7.8 Kokoxili earthquake struck the northern Tibetan Plateau on 14 November 2001, rupturing over ~400 km in total along the western section of the Kunlun fault. Significant, large-scale postseismic surface displacements have been geodetically observed using InSAR and GPS data in the ~9 years (2001-2010) following the Kokoxili earthquake, which provides important constraints on the rheology properties of the Tibetan Plateau. In this study, we model the time-dependent postseismic displacements following the Kokoxili earthquake, including both GPS (2001-2002 for near-field and 2001-2010 for far-field) and descending-track InSAR line-of-sight timeseries (2003-2010) to study three postseismic deformation processes. Far-field postseismic deformation (> 200 km from rupture) is primarily induced by upper mantle viscoelastic relaxation beneath Tibet and the Qaidam Basin and places a lower bound on transient and steady-state viscosities on the order of 10¹⁹-10²⁰ Pas. Shallow stress-driven afterslip (<20 km) on the Kunlun Pass fault generates deformation patterns in the near-fault area and helps explain GPS-measured displacement gradient across the fault, which improves the fit to the early GPS data in the near-fault area. Deep stress-driven afterslip just beneath the downdip region of the coseismic rupture (>20 km) has an amplitude of ~1 m during the first 3 years. Our results also indicate that the consideration of deep afterslip increases our estimates of transient viscosity of the lower crust beneath Tibet and the Qaidam basin for this earthquake by as much as a factor of three. Our combined model incorporating viscoelastic relaxation and afterslip suggests that the effective transient and steady-state viscosities in the Tibetan lower crust are 5×10¹⁸ Pas and 4 ×10¹⁹ Pas, respectively (transient viscosity=2×10¹⁸ Pas without afterslip considered), while the effective transient and steady-state viscosities below the Qaidam Basin area are 1×10¹⁹ Pas and 6 ×10¹⁹ Pas (transient viscosity=4×10¹⁸ Pas without afterslip considered).

Presenting Author: Dezheng Zhao

Student Presenter: Yes

Authors