Probing the rheology of continental faults: Decade of post-seismic InSAR time-series following the 1997 Manyi (Tibet) earthquake

Abstract

The physical processes driving post-seismic deformation after large earthquakes are still debated. As in most cases relatively short observation time periods are being used, it is still challenging to distinguish between the different proposed mechanisms and therefore a longer observation time is needed. The 1997 MW 7.6 Manyi, Tibet, earthquake has an excellent InSAR data archive available to study the post-seismic deformation up to ~13 yr after the earthquake. The coseismic and early post-seismic phases of theManyi earthquakewere already investigated in detail by numerous studies with viscoelastic and afterslip models being used to explain the post-seismic deformation. We use SAR (Synthetic Aperture Radar) data obtained from the ERS and Envisat satellites covering the central part of the Manyi fault from 1997 to 2010 to significantly extend the observation period. We test different viscoelastic (uniform Maxwell, Standard linear solid and Burgers body rheology below an uppermost elastic layer) and afterslip models to assess the most suitable mechanism for post-seismic deformation. While a Maxwell rheology (misfit = 2.23 cm) is not able to explain the observed long timeseries, the standard linear solid (misfit=2.07 cm) and Burgers body models (misfit=2.16 cm) with two relaxation times, cannot reproduce sufficiently the localized deformation patterns. The afterslip model (misfit = 1.77 cm) has the lowest misfit and explains well the temporal and spatial pattern of observed deformation. A combined mechanism model that considers the effects of both afterslip and viscoelastic relaxation is also a feasible process, where the viscoelastic relaxation can slightly improve the fit to the data especially at larger distances from the fault. Themaximum average line-of-sight velocity is~4mmyr-1 during 2008-2010, suggesting that the post-seismic deformation of the Manyi earthquake might be vanishing and gradually stepping into an interseismic phase.