Post-seismic Motion Following The 2008 Nima-Gaize (Tibet) Earthquake Constrained By InSAR Observations

On 9 January 2008 a Mw 6.4 normal-faulting earthquake occurred in central Tibet,near the border of Nima and Gaize counties and just north of the Bangong-Nujiang su-ture zone.A week later,a Mw 5.9 aftershock occurred a few kilometers to the northwest of the main shock.This earthquake provides us with a unique opportunity to examine the normal fault in southern Tibet and the crustal structure of this region using InSAR data.Here we consider interferometric synthetic aperture radar?InSAR?data from the European Envisat satellites,covering both the co-seismic phase and 723 days of post-seismic deformation.We performed inversion for distributed slip on a pair of fault planes corresponding to the rupture surfaces of the main shock and primary aftershock based on former researches,the inversion result shows the maximum slip on the main shock plane is 1.07 m,and the maximum slip on the aftershock plane is 0.59 m.The slip of the main shock plane is mainly distributed at?5,10?km depth and the slip of the aftershocks plane is mainly distributed at?2,4?km depth.The post-seismic deformation time series obtained by InSAR time series analysis show that the post-seismic defor-mation pattern is similar to that of the co-seismic phase,which that the afterslip is the most likely physical mechanism responsible for post-seismic deformation.The post-seismic inversion for afterslip on the main shock and aftershock fault planes shows the slip distributes at the comparable depth of the coseismic slip,and the deep slip is not obvious.The maximum cumulative slip on the main shock plane is 9.3 cm,and the maximum cumulative slip on the aftershock plane is 3.3 cm,which is about one order of magnitude smaller than the coseismic slip.By comparing the residual between the forward modeling of the afterslip and the postseismic deformation time series,it can be concluded that the post-seismic deformation is mainly caused by the afterslip.Models of viscoelastic stress relaxation in a Maxwell half-space place a strong lower bound on midcrust to lower crustal viscosity of 6 × 10¹⁷ Pa·s...