Vertical Movement Model in Chinese Mainland Based on First Order Leveling Results

  Objectives  The national first order leveling results are valuable data for studying the vertical movement of crust in Chinese Mainland. The trend of vertical movement in the past 50 years is analyzed with three period results of first order leveling network of China.

  Methods  Firstly, on the same reference datum, a static adjustment method is used to calculate the height of the first order leveling points. By analyzing the location, height difference and record of leveling points, the coincidence points of different period results are obtained. Then the velocity of leveling coincidence points can be calculated by height difference and time span. Secondly, the residual distribution of checking points and fitting points is used to evaluate the pros and cons of the interpolation methods, such as Hardy function interpolation, Kriging interpolation and inverse distance weighted method, one of which is determined to establish vertical movement model. Finally, the vertical movement model in Chinese Mainland is obtained with the method of Kriging interpolation.

  Results  The residual distribution of checking points and fitting points shows that the fitting precision of Hardy function is slightly lower but more stable than other methods. And the precision of inverse distance weighted method is slightly higher, but there are some outlier in the fitting results. The valid fitting region of triangulation with linear interpolation is the smallest convex polygon consisting of the outermost leveling points, so the blank area near the boundary of Chinese Mainland is existed. The precision is basically equal between Kriging interpolation and minimum curvature interpolation, but from the perspective of the residual, Kriging interpolation is slightly better.

  Conclusions  From the vertical movement model, the characteristic of vertical movement is qualitatively analyzed: In the past 50 years, the North China Plain, Jiangsu-Shanghai Area, Fen-Wei Basin, Xinjiang and Hainan are subsiding. Among them, the North China Plain and Jiangsu-Shanghai Area are severe subsiding condition with the velocity of 40.4±1.4 mm/a. The south of Tibet, North-East China, Fujian and north of Shaanxi are uplifting, and the trend of uplifting is kind of fierce in the south of Tibet and east of North-East China, the velocity of uplift is 5.4±2.5 mm/a. Other areas such as South China are relatively stable.