CONTRASTING CLIMATIC AND TECTONIC INTERPLAYS IN THE QILIAN SHAN AND THE TIEN SHAN FROM SENTINEL-1 VELOCITIES

We apply big data analytics to Sentinel-1 radar satellite data acquired between 2014 and 2023 to capture the Earth’s surface deformation over the Qilian Shan and the Tien Shan. These surface deformation signals come from processes in the lithosphere, cryosphere and hydrosphere caused by active tectonics, global warming, and human activities. Having mapped 2 million km2 of large-scale velocity fields over the Qilian Shan and the Tien Shan, we found different characteristics in the the vertical velocities, revealing contrasting behaviours in the tectonic and climatic interplays over these two regions onlythree-degreee latitudes apart from each other. Although in both regions we expect tectonic uplift due to the Indo-Eurasia collision, we observed mostly subsidence over the Qilian Shan but uplift over the Tien Shan. The subsidence rates over the Qilian Shan reach over 10 mm/yr whereas the uplift rates over the Tien Shan exceed 5 mm/yr at its peak. We interpret the subsidence over the Qilian Shan to be dominated by permafrost thaw as the spatial distribution of the subsidence pattern correlates precisely with the predicted permafrost distribution. However, despite the presence of permafrost over the Tien Shan, we observed uplift instead. One difference between the cryospheric settings in these two regions is that the Tien Shan is snow-covered whilst the Qilian Shan is mostly not. This suggests that whilst the vertical motion across the Qilian Shan might be dominated by permafrost subsidence, the deformation over the Tien Shan is more complicated. It is worth noting that the highest peak of the Tien Shan, where we measured the highest uplift rates, is also where the glaciologists measured the most rapid glacial thinning rates. Although glaciers are seated at the bottoms of individual valleys, the uplift signal we measure is over 250 km wavelength, suggesting isostatic rebound due to rapid ice loss. We also observe a step change in the vertical velocity that reveals a previously unmapped active fault bounding the highest peak. The 2.4 mm/yr relative uplift rate across this fault is relatively high in geological terms. One possible explanation is that the thrust motion on the fault might be promoted by the isostatic rebound induced by global warming, suggesting an intricate interplay between tectonics and climate change in the present day. Further modelling is needed to test this hypothesis.