Current slip rates on conjugate strike-slip faults in central Tibet using synthetic aperture radar interferometry

Abstract

We estimate the current slip rates on active conjugate strike-slip faults in central Tibet using repeat-pass synthetic aperture radar interferometry (InSAR). The conjugate fault systems are centered along the east trending Late Jurassic–Early Cretaceous Bangong-Nujiang suture zone and are composed of NE striking left-slip faults to the north and NW striking right-slip faults to the south. The surface displacement field obtained from InSAR data show 30- to 60-km-wide zones of concentrated shear that coincide with active fault traces observed in the field. The radar data indicate that, within a 200- to 300-km-wide belt, the deformation regime defined by the conjugate strike-slip faults is accommodating ∼5 mm yr−1 of pure shear contraction oriented in the N10°E direction and ∼6 mm yr−1 of right-lateral simple shear in the N110°E direction. The observation of localized strain along faults indicates that faulting is the dominant mode of deformation in central Tibet with seismogenic depths extending down to ∼25 km. Furthermore, extrapolating the current slip rates estimated for the central Tibet faults, the total magnitude of fault slip based on geological observations would only require the faults to have initiated sometime in the past 2–3 Myr. This appears to contradict the few geochronologic constraints on fault initiation at 8 Ma or even earlier. This discrepancy suggests that the fault slip rates may not have remained constant through time but have accelerated in the recent period. With the exception of the slip rate on the Gyaring Co fault, the slip rates that we determined on the conjugate strike-slip faults in central Tibet are significantly slower than the rates on faults that bound the Tibetan Plateau, such as the left-slip Altyn Tagh fault to the north. This observation suggests that although deformation is active within central Tibet, plateau-bounding structures are dominant in absorbing Indo-Asian convergence.