Gravity and GPS hybrid measurements were conducted at 385 stations throughout the Qinling Orogen, China, to update Bouguer gravity anomalies and free‐air gravity anomalies of the area. The crustal density structure, lithosphere flexure mechanism, and isostatic state of the Qinglin Orogen were studied in detail via these in situ observations. Bouguer gravity anomalies in the study area are mainly negative, ranging from −410 mGal in the Tibetan Plateau to −100 mGal in the eastern Qinglin Orogen. The estimated crustal thickness ranges from 56 to 35 km and thins eastward along the Qinling Orogen. The optimal effective elastic thickness (Te) of the study area is 14 km, and the loading comes from the Earth's surface, the interface between the upper and lower crust, and the Moho. Vertical tectonic stress borne by the lithosphere varies observably in the study area. Downward stress reaches a peak of −14 MPa in the Liupanshan Mountains, whereas the highest value of upward stress (8 MPa) is attained in the middle Qinling Orogen. Considering distributions of crustal density structures and vertical tectonic stress of the lithosphere, in addition to the distinct loading ratios of the eastern and western Qinling Orogen, a piecewise combination model was developed to interpret the uplift of the Qinling Orogen. This model shows that the eastern part of the Orogen is thickened by the upward migration of mantle materials under the thrusting of the South and North China Blocks, whereas uplift of the western part results from lower crustal flow derived from the Tibetan Plateau.

We built the first dense gravity network including 107 stations around the Tsangpo Gorge, Tibet, one of the hardest places in the world to reach, and conducted a gravity and hybrid GPS observation campaign in 2016. We computed the Bouguer gravity anomalies (BGAs) and free‐air gravity anomalies (FGAs) and increased the resolution of the FGAs by merging the in situ data with EIGEN‐6C4 gravity model data. The BGAs around the Tsangpo Gorge are in general negative and gradually decrease from south (−360 mGal) to north (−480 mGal). They indicate a uniformly dipping Moho around the Tsangpo Gorge that sinks from south to north at an angle of 12°. We introduced a method to compute the vertical tectonic stress of the lithosphere, a quantitative expression of isostasy, using BGA and terrain data, and applied it to the area around the Tsangpo Gorge. We found that the lithosphere of the upstream of the Tsangpo Gorge is roughly in an isostatic state, but the lithosphere of the downstream exhibits vertical tectonic stress of ~50 MPa, which indicates the loss of a large amount of surface material. This result does not support the deduction of the valley bottom before uplift of the Tsangpo Gorge by Wang et al. (2014).

The current work describes the combined data of three field campaigns, spanning 2009-2013. Their joint gravity and GPS observations thoroughly cover the sites of lithospheric flexure between the Sichuan Basin and the Eastern Tibetan Plateau. The study area's free-air gravity anomalies (FGAs) are updated by using a remove-and-restore algorithm which merges EGM2008 data with in situ observations. These new FGAs show pairs of positive and negative anomalies along the eastern edges of the Tibetan Plateau. The FGAs are used to calculate effective elastic thickness (T e ) and load ratios (F) of the lithosphere. Admittance analysis indicates the T e of Longmen Shan (LMS) to be 6 km, and profile analysis indicates that the T e of the Sichuan Basin excesses 30 km. The load ratio (F 1 = 1) confirms that the lithospheric flexure of the LMS area can be attributed solely to the surface load of the crust.

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