Stusy of dynamics of the Earth's deep interior based on the global network of superconducting gravimeters

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1. It was agreed that the observing period of GGP (Global Geodynamics Project) should be from July 1997 to June 2003. Accordingly, final adjustments of the instruments were done. The gravity data from the Japanese stations are already available for exchange, and were used for earth tide analysis. As a result, it was found that common signals presumably originating from the atmosphere exist in plural gravity residuals. This demonstrate that there is much to be studied for estimating the atmospheric contribution on the gravity.2. A new superconducting gravimeter was installed in Australia by National Astronomical Observatory. Also, colleagues at Kyoto University are planning to move one of the two superconducting gravimeters installed at Kyoto to a new site in Indonesia within 1997. These new gravity stations, together with the existing stations in the Syowa station, Antarctica and in the Japan mainland, form a large scale network from the west Pacific to Antarctica. In addition, these new stations will contribute much to the global coverage of superconducting gravimeters, which is essential to the GGP network.3. Gravity change associated with the polar motion of the Earth (pole tide) was observed from the superconducting gravimeter data acquired at Syowa station, Antarctica. The period and the attenuation parameter of the Chandler motion were estimated with good precision. However, there were discrepancies between the observed values of the delta-factor and the phase and the theoretical predictions. This was attributed to the effect of the atmosphere and the ocean.4. Spectral analysis of the superconducting gravimeter data from Syowa station, Antarctica revealed that there exist some power corresponding to the elastic normal modes of the Earth even without any large earthquakes. This implies that free oscillations of the Earth are continuously excited. The possible sources of excitation include the global atmospheric changes.