On The Deflection Of The Vertical Change

The movements of the material in the Earth arouses the redistribution of its density, which results in the variations of gravity field at a point with the time going. Meanwhile, the plumb-line deviation at the same point varies correspondly, which is called variation of the plumb-line deviation. It includes tidal variation and non-tidal variation. This paper involved only the latter, namely non-tidal variation in the deflection of the vertical, which is abbreviated for variation of plumb-line deflection(Plumb-line variation, PLV).There are much information about the physical state within the earth in the variation of gravity field, which can be studied through PLV. At the same time, studying PLV will play an important role in the development of geodynamics. In this dissertation, the history and current situation of the PLV's researching are introduced, especially about the phenomena relevant to PLV during studying natural disasters such as EI Nino phenomena and earthquakes. This work emphasises on PLV's precision. The formulae to calculate PLV are compared and it is shown that the formula on time-variation of gravity potential(W) is perfect. At present, the accuracy of time-variation of plumb-line deflection can be attained to 0″.005 and the influence from far area can be ignorable. A simulation on the characteristics of the data from the gravimetric network in North China and in West Yunnan is done. The conclusions are: 1.it can be verified that the precision of PLV averages between 0."0055 and 0."0062,with 0″.005 in the same order of magnitude. 2.it can be used 5′×5′gravity layouting in standard network. 3. it is reasonable to gridding in such resolution to calculate in non-standard network. 4. the accuracy of PLV in every point in the same network is determined directly by distribution of the points around it but has not much relation with the point amount in the whole network. Although there has been a long history of studying PLV, it is blindfold to some extent because it lacks related observation. We set some results in this research, but we also face the same problem that is short of earth observation. Finally, some prospection on further study are discussed.