Slip variability along the East Kunlun Fault in eastern Tibet, revealed by InSAR and GNSS

Determining slip rates along the tectonic fault is essential for understanding its deformation mode and assessing the future seismic hazard. Benefited from the Copernicus Sentinel-1 series mission, we are now able to derive large-scale, high-resolution, and three-dimensional velocity fields by integrating Global Navigation Satellite System (GNSS) and Interferometric synthetic aperture radar (InSAR). The East Kunlun Fault is the northern border of the Bayan Har Block in the eastern Tibetan Plateau, which is approximately 1500 kilometers long and has hosted 4 M>6 earthquakes in the past century, including the 2001 Mw 7.8 Kokoxili earthquake. There are two seismic gaps on this fault, raising our concerns regarding its future earthquake hazard.

Here, we process 10 years (2014–2024) of Sentinel-1 SAR data to obtain the line-of-sight (LOS) velocity fileds covering ~0.65 million km², using the COMET LiCSAR automated processing system. The InSAR velocities are transformed into the fixed Eurasian reference frame by fitting a planer ramp to the differences between InSAR and GNSS LOS velocities. We develop an algorithm to tie InSAR velocity frames together in regions lacking efficient GNSS observations. Using the GNSS-interpolated north velocities as prior constraints, we decompose InSAR ascending and descending velocities into east and vertical components. We observe long-wavelength tectonic signals from InSAR east velocity map, including clear slip gradient across the East Kunlun Fault, and postseismic deformation associated with the Kokoxili earthquake.

We apply four analytical models within a Bayesian inversion framework to estimate slip rates along the East Kunlun Fault: a simple screw dislocation model, an interseismic and afterslip coupling model, a shallow and deep creeping coupling model and a shear zone model. Our results indicate up to 26.4 mm/yr postseismic slip in western segment of the fault, and 1.3–2.4 mm/yr shallow creep in the eastern segment. The InSAR east velocity show a slip decrease from the west to east, with the magnitude from ~14.5 mm/yr to ~4.5 mm/yr, in agreement with some geological slip rates. Additionally, our results suggest the presence of a potential shear zone beneath the fault, with a width of up to ~100 kilometers. Further investigation is required  to determine the mechanisms of the shear zone: whether it results from postseismic deformation or reflects underlying geological processes.