Gravity evidence of underplating in the northeastern margin area of Qinghai-Tibet plateau

:Based on leveling data in 1972–2011 and relative-gravity data in 1993–2011, we obtained a long-term vertical crustal-deformation rate of 1. 62 mm/a and a relative-gravity variation rate of 0.62 × 10 − 8 ms− 2a− 1 for the northeastern margin area of Qinghai-Tibet plateau. After removing the contributions from the observed vertical movement and inferred surface denudation, we obtain a gravity-variation rate of 0.73 × 10− 8 ms− 2a− 1 attributable to the mass changes beneath the crust. This positive change suggests that the total mass under the observation stations was gradually increasing. We consider this result to be the gravitational evidence of under-plating beneath the study area, and propose that the underplating was caused by collision betwen the Indian plate and Tibetan plateau and by gravitation-potential induced deviatoric stress.