Comparison Research on Gravity Changes in Indonesia, China and Japan by Employing Superconducting Gravimeters

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Precise gravity measurements using superconducting gravimeters (SGs) are expected to be an effective measure for detection of very weak signals caused by oscillations in the Earth's fluid core, or long-term gravity changes due to tectonic motions related to seismic and volcanic activities. A global network of SGs was set up by Global Geodynamic Project (GGP), an international program of observations of temporal variations in the Earth's gravity field, under the sponsorship of IUGG and IAG. Data distribution of the network began in 1997. It is of course important to improve global geodynamic studies focused on Earth's deep interior using data of the SG global network. On the other hand, it is desired to investigate regional characteristics of physical properties and structures in crust and upper mantle in East Asia using SG data in Indonesia, China and Japan by means of comparison of loading effects of ocean tides on Earth tide observation in these areas. Kyoto University has carried on … More precise gravity observation using two SGs since 1988. In 1997, we shifted one of the two GSs from Kyoto to Bandung, Indonesia. Since then, SG observation in Bandung has been continued under close cooperation between Kyoto Univ. and Volcanological Survey of Indonesia. In this study, we, Japanese investigators visited Bandung every half a year for maintenance of the SG, and Indonesian investigators visited Kyoto every year to analyze the SG data and to discuss problems on gravity changes in tectonically active regions along island arcs. The head investigator (S. Takemoto) visited the Institute of Geodesy and Geophysics, Chinese Acad. Sci. in Wuhan in November 1999 and discussed with Chinese investigators our cooperative research of geodynamics in East Asia using superconducting gravimeters and absolute gravimeters. We could establish a data set of the superconducting gravimeters in Bandung, Wuhan and Kyoto. As a result of comparison of these data, regional difference of loading effects of ocean tides on Earth tide observation can be indicated. Less