Preliminary results from permanent GPS array by the Geological Survey of Japan in conjunction with groundwater-level observations

A regional continuous Global Positioning System (GPS) array consisting of u niform antenna type, has been established by the Geological Survey of Japan (GSJ) mainly around the Kansai district. Geodetic results for 2.5 years da ta are as follows. In comparison with the solutions obtained from the Geogr aphical Survey Institute (GSI) continuous GPS array which employs different type of antenna from the GSJ's array, it was found that the agreements bet ween the daily positions were about 10 mm in horizontal and 15 to 20 mm in vertical components. This result indicates that the influence of the antenn a type difference is at this level. The GSJ's GPS stations around the Kansa i district were found to have a common annual variation in the vertical com ponent, whose amplitude was different from site to site. There were small c orrelations with in situ measurements of groundwater-level variation, excep t for the two stations whose annual variations of the GPS vertical componen t were the largest. The vertical displacements due to elastic deformation b y groundwater-pressure changes in the aquifers were estimated using a simpl e model, but they were too small to account for the observed variations.