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

1. 全球地球动力学项目（GGP）的观测周期为1997年7月至2003年6月。因此，对仪器作了最后的调整。来自日本台站的重力数据已经可供交换，并被用于潮汐分析。结果发现，假定来自大气的共同信号存在于多重重力残差中。这表明，要估计大气对重力的贡献还有许多工作要做。澳大利亚国家天文台安装了一台新的超导重力仪。此外，京都大学的同事们正计划在1997年将安装在京都的两个超导重力仪中的一个搬到印度尼西亚的一个新址。这些新的重力站，连同在Syowa站、南极洲和日本大陆的现有台站，形成了一个从西太平洋到南极洲的大规模网络。此外，这些新台站将大大有助于超导重力仪的全球覆盖，这对GGP网络至关重要。利用南极Syowa站的超导重力仪数据，观测了地球极运动（极潮）引起的重力变化。对钱德勒运动的周期和衰减参数进行了较高精度的估计。然而，delta因子和相位的观测值与理论预测值存在差异。这被归因于大气和海洋的作用。对南极Syowa站超导重力仪数据的频谱分析表明，即使没有大地震，也存在与地球弹性模态相对应的能量。这意味着地球的自由振荡是不断被激发的。可能的激发源包括全球大气变化。

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.