GGP (Global Geodynamics Project): an international network of superconducting gravimeters to study time- variable gravity

The Global Geodynamics Project (GGP) is an international network of superconducting gravimeters (SG) first established in 1997 and further extended in 2003. It was decided during the last IUGG assembly in 2007 to move to a permanent network hosted by IAG and become part of GGOS. Several new locations are being planned to extend the network to about 30 stations in 2008/2009. One of the present tasks within GGP is to prepare raw GGP data (at sampling times of 1-5 s) for inclusion into the IRIS data set for the seismologists to include in normal mode studies of the Earth. Of continuing interest within GGP is the issue of combining measurements from absolute gravimeters and permanent GPS at the SG stations for a variety of long-term studies of the gravity field such as tectonic uplift, subduction zone slip, post-glacial rebound and present-day ice melting. One of the most interesting new ideas within GGOS is the determination of the geocenter using a combination of satellite and groundbased gravimetry. The GGP network can provide a unique contribution in this respect through continuous data at the stations where absolute gravimeters (AG) will be deployed. The continuous monitoring of timevariable gravity is a tool to investigate many aspects of global Earth dynamics and to contribute to other sciences such as seismology, oceanography, earth rotation, hydrology, volcanology, and tectonics. Another promising application is the use of SG subnetworks in Europe and Asia to validate time-varying satellite gravity observations (GRACE, GOCE) due to continental hydrology and large-scale seismic deformation.