Interseismic strain accumulation across the Manyi fault (Tibet) prior to the 1997 Mw 7.6 earthquake



[1] The coseismic displacements caused by the Mw 7.6, 1997 Manyi strike-slip earthquake have been extensively studied. In order to assess whether the current deformation around the Manyi fault is due to one or more postseismic mechanisms and to constrain the rate-state models of afterslip, an estimate of the interseismic motion across the fault prior to the earthquake is needed. We use ESA ERS data to form 20 interferograms covering the five year period of 1992–1997, which are combined using a multi-interferogram method to calculate a map of line-of-sight velocities. Inverting this velocity map using a Monte Carlo method, we estimate relative motion across the fault of 3 ± 2 mm/yr prior to the 1997 earthquake, one third the rate of other major faults in the area such as the Kunlun and the Altyn Tagh faults. The locking depth is poorly resolved, but is estimated to be 22 ± 15 km. The localised pattern of deformation observed suggest that the viscosity of the lower crust and upper mantle in the Manyi area is greater than 4 × 1018 Pa s proposed by previous postseismic studies of the area. We find no evidence of significant deformation across possible westward extensions of the Kunlun Fault. These rates of interseismic deformation are much smaller than the rates still being observed today, 10 years after the event, indicating the current rates must be due to one of the postseismic deformation mechanisms.