Extending InSAR Measurements of Postseismic Deformation for the 1997 Manyi Earthquake with ENVISAT

Its location at high altitude and amidst limited relief has allowed a coherent time series of postseismic deformation for the 1997 Manyi earthquake, Tibet, to be constructed using ERS SAR data spanning an interval of up to four years after the earthquake (Ryder et al., 2006). The time series can be inverted for distributed afterslip; along-strike correlation of co-seismic and post-seismic slip maxima provide support for afterslip as a plausible mechanism. The deformation timeseries can also be modelled by stress relaxation in a viscoelastic medium underlying an elastic lid. Reasonable fits are obtained for rheologies with two different timescales, allowing faster relaxation at short times after the earthquake. Purely Maxwell viscoelastic models require increasing viscosities to fit the deformation at increasing times, behaviour that might be consistent with a non- linear viscosity. We have extended the InSAR measurements of postseismic deformation for the Manyi earthquake to up to eight years after the earthquake using ENVISAT ASAR data. Although the signal is small, a pattern of deformation similar to the earlier ERS time series is clearly visible. These longer term observations of the postseismic deformation will allow further discrimination among the various models. Ryder, I., B. Parsons, T. J. Wright and G. J. Funning, Postseismic motion following the 1997 Manyi (Tibet) earthquake: InSAR observations and modelling, Geophys. J. Int., 2006.