抄録
Tidal gravity observations were made at Syowa and Asuka Stations, Antarctica, during wintering of the 28th Japanese Antarctic Research Expedition. LaCoste & Romberg type G gravity meters with electrostatic feedback amplifiers were used. The feedback voltage outputs were recorded every 30 minutes for both stations. The data with stable drift were selected and calibrated to tidal gravity variation. The number of selected data is 2976 from April 1 to June 1, 1987 for Syowa Station, and is 8656 from June 3 to November 30, 1987 for Asuka Station. The obtained tidal gravity data were analyzed by using the 'BAYTAP-G' program and oceanic tidal loading effects were corrected for by using the 'GOTIC' program. The a factors which are corrected for oceanic tidal loading effects distribute from 1.130 (K1) to 1.250 (M2) for Syowa Station, and from 1.134 (P1) to 1.330 (K2) for Asuka Station. For diurnal tides, there is no significant difference between the observed o factors and the theoretical values predicted by the Water's formulas. For semi-diurnal tides, how-ever, the observed a factors at both stations are larger than the Water's predictions by 10%-14%. The 8 factors at Asuka Station on the ice sheet (about 1, 000 m thick) are generally larger than those at Syowa Station on the basement rock of the East Ongul Island in Lutzow-Holm Bay. Since shorter period constituents (semi-diurnal tides), which reflect shallower crustal structures, deviated from the theoretical 8 factors to more positive values as compared with longer period constituents (diurnal tides), easily deformable ice sheet may have played an important role in the observed large 8 factors of semi-diurnal tides in the Antarctic region. The larger admittance of gravity change for atmospheric pressure at Asuka Station (-0.27 Fugal/mb) than that in mid-latitude observations (-0.35--0.37 Fugal/mb) may also be explained by easy loading deformation of the ice sheet by air mass for an extent of 30 km covering the site. However, detailed examination of the earth models including surface ice layers and comparison of the a factors for the fortnightly and ter-diurnal constituents with those for the diurnal and semi-diurnal constituents have to be made for accurate interpretation of the frequency dependence of the 8 factors in the Antarctic region.
