Abstract
Continuous observations of tidal variation of gravity were carried out at Shizuoka during the period of about 11 months from September 1984 to July 1985 by employing two LaCoste & Romberg gravimeters D-58 and G-680 installed side by side on the same concrete base. As effects caused by disturbed factors such as ambient temperature, atmospheric pressure and oceanic tides to the gravimeters installed on the same point are practically common, it is expected that their data will give similar results. In practice, however, δ-factors derived from the data of about 11 months by the gravimeter G-680 are slightly larger than those by the gravimeter D-58 for almost all tidal constituents, and their variations with time are not so similar. These causes are left unsolved at present. Comparing the δ-factors derived from about two-years' data, which were fully covered the period of the simultaneous observations with both gravimeters, by the gravimeter D-58 with those from about 11-months' data, both were in good agreement as well as about 0.1%. It was certainly found that the results derived from the data of about one year were fully stable and that those were reliable. For the purpose of earthquake prediction, the relation between the length of data and the difference of δA-factors obtained by both gravimeters was thoroughly examined. It was also shown by using the data of a duration longer than 30 days that the differ ences of the 5-factors were relatively stable, but that the amount of their fluctuations was considerably large.
