Leveling Results in the Tokai Region and the Estimation of the Accuracy of Leveling Based on Them

This paper contains two subjects.In the first half of this paper, the leveling results in the Tokai region including the Kakegawa-Omaezaki route are summarized.There has been a long continuing subsidence focus centered at the western part of Suruga Bay. As a result, the subsidence of Omaezaki relative to Kakegawa has been observed. It is accompanied by an apparently seasonal up-and-down movement. It seems likely that the vertical movement pattern over the region showed a rapid and considerable change at around 1980. A recognizable decrease in the relative subsidence rate over the route is found. The subsidence focus appears to have vanished.In the second place, a discussion is given on the accuracy of geodetic leveling on the basis of the results in the region as well as whole land survey results.An essential problem in this subject is to find a cause of inequality between U_r and U_p. U_r denotes the standard error derived from discrepancy of forward and backward levelings over a section. U_p is that from circuit misclosures. It has been believed that it is due to a systematic error involved in leveling. But examination of the leveling results suggests that U_p approaches U_r as the time required to complete the measurement along each circuit becomes shorter. The inequality should be attributed to crustal movements which took place while the survey was carried out. It appears that the systematic error is much less and the accuracy of leveling can be fundamentally estimated by U_r.