江刺地球観測施設における潮汐歪の観測

抄録

The tidal strain has been observed at Esashi Earth Tides Station which designed for earth tides observations. The station is located in the middle of Mt. Abara (780 m above mean sea level). Three extensometers made of quartz tubes 30 mm in diameter and 36, 36 and 51 m in length are installed in the vault in NS, EW and NW directions respectively. The detector of these extensometers is a differential transformer. Routine observations were begun in June 1979. Preliminary records from the end of April 1979 to the begining of June 1979 show the drifts of 4X10^-8/month for NS and EW components and 2X10^-8 for NW component. These drifts are probably of instrumental origin. The data of NS and EW components for the period during June to August 1979 are analyzed in two steps. The first one is the estimations of the amplitudes, their factors and phase differences of the observed data by least square fitting to the theoretical strain waves which are derived from the potential developed by Cartwright, Tayler and Edden. In these analysis the drift and non-tidal variations are removed by using Pertzev's filter. The standard deviation of a single observation has been found to be 2X10^-8 in both components, which exceeds about 70 times the value as compared with the accuracy of the calibrations of the instruments or the reading errors. The second is the analysis of residuals obtained by subtracting the above estimated tidal strain waves from the original data. These residuals show broad shaped power spectra at the tidal bands and high powers at the low frequency band. The AR-response method is applied to the ahalysis of the relations between the residuals and the changes of the atmospheric pressure. The results suggest the existences of coupling between them but the physical interpretation is a problem of further investigations.