Relaxation of Tibetan Lower Crust and Afterslip Driven by the 2001 Mw7.8 Kokoxili, China, Earthquake Constrained by a Decade of Geodetic Measurements. Issue 4 (31st March 2021)

• Record Type: Journal Article
• Authors: Zhao, Dezheng; Qu, Chunyan; Bürgmann, Roland; Gong, Wenyu; Shan, Xinjian
• Is Part Of: Journal of geophysical research. Volume 126:Issue 4(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-03-31
• Subjects: Kokoxili earthquake -- Kunlun fault -- postseismic deformation processes -- stress‐driven afterslip -- viscoelastic relaxation; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2020JB021314
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: We model the time‐dependent postseismic displacements following the 2001 Mw7.8 Kokoxili earthquake, including both GPS (2001–2002 for near‐field and 2001–2010 for far‐field) and descending‐track InSAR line‐of‐sight time series (2003–2010) to study three postseismic deformation processes. The predicted deformation patterns and magnitude from poroelastic rebound are inconsistent with the geodetic observations. 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 10 19 –10 20 Pas. Shallow stress‐driven afterslip (<20 km) on the Kunlun Pass fault localizes deformation in the near‐fault area and helps explain the GPS‐measured displacement gradient across the fault. Deep stress‐driven afterslip in the downdip region of the coseismic rupture (>20 km) has an amplitude of ∼1 m during the first 3 years. Our results 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 × 10 18 Pas and 4 × 10 19 Pas, respectively (transient viscosity = 2 × 10 18 Pas without afterslip considered), while the effective transient and steady‐state viscosities below the Qaidam Basin area are 1 × 10 19 Pas and 6 × 10 19 Pas (transient viscosity = 4 × 10 18 Pas without afterslip considered). Key Points: Remarkably asymmetric postseismic deformation following the 2001 Kokoxili earthquake reveals contrasting rheology across the Kunlun fault Deep afterslip localized in the shear zone increases the estimate of lower‐crustal transient viscosity Shallow afterslip helps explain GPS‐measured displacement gradient across the Kunlun Pass fault