Abstract
Since Dec. 1976, EDM (electro distance measurements) has been repeated at an interval of 1-2 months at the Futagawa base-line network installed in Toyohashi city, central Japan. Directions of base-lines are roughly aligned to the direction of contraction in this region. At Futagawa network, measurements have been conducted as much as possible under good meteorological conditions. The following conclusions are obtained. 1) During the period of 1977-1978, the rate of contraction in the direction of NW-SE at Futagawa network amounts to (0.9-1.3) × 10-6/year. This rate of contraction is consistent with such data obtained from other base-lines in the Tokai region with the same direction. 2) When the temperature gradient of lower atmosphere is low, the errors of EDM are almost within ±1.0×10-6. 3) In order to keep the errors within ±1.0×10-6, the correction for the frequency change of the instruments and the water vapour pressure can not be neglected.
