Temporal and spatial movement characteristics of the Altyn Tagh fault inferred from 21 years of InSAR observations

We use 21 years of interferometric synthetic aperture radar data obtained between 1996 and 2017 from three European Space Agency satellites, namely the European Remote Satellite (ERS), Environmental Satellite (ENVISAT) and Sentinel-1, to estimate the present-day strain accumulation rate within the central segment of the Altyn Tagh fault (ATF) along the northern boundary of the Tibetan Plateau. We obtain the first Sentinel-1 line-of-sight velocity map, thereby revealing a velocity gradient across the main ATF. Due to significant near-fault deformation, which cannot be modeled by utilizing only the classic Savage deep slip model, a dislocation extending to a certain depth representing strain release by shallow creep is combined with a deep screw dislocation to model the observations. The best-fitting results are a 9.0 mm/year slip rate with a 20.0 km locking depth and a 2.0 mm/year creep rate with a 2.0 km creep extent for the ERS data, a 7.4 mm/year slip rate with an 18.0 km locking depth and a 1.8 mm/year creep rate with a 2.8 km creep extent for the ENVISAT data, and a 6.0 mm/year slip rate with a 21.0 km locking depth and a 1.5 mm/year creep rate with a 1.0 km creep extent for the Sentinel-1 data based on a single fault inversion. The slip rate decreases with time along this section of the ATF, while the creep rate varies around 1.8 mm/year, which does not constitute an obvious variation. In the spatial domain, the fault was divided into three segments, only Sentinel-1 data were used in the inversion, and the best-fitting values for the slip rate, locking depth, creep rate and creep extent are [7.4, 21.0, 1.8, 1.5], [6.8, 23.0, 1.5, 1.0] and [5.3, 20.0, 2.0, 1.1] for the Kuyake segment, Kulukuole segment and Aqiang segment, respectively. We conclude that deep slip motion within the ATF was variable in both the time domain and the space domain, whereas shallow creep, which must be accounted for using the Fattahi model considering both deep and shallow motions, was stable at ~ 2.0 mm/year with a creep extent of 1.0–2.0 km. The seismic moment release rate is less than 9.0% of the geodetic moment accumulation rate, which indicates a high seismic risk within the ATF.