David Lavallée, Geoffrey Blewitt, Peter J. Clarke, Konstantin Nurutdinov, William E. Holt, Corné Kreemer, Charles M. Meertens, Wayne S. Shiver, Seth Stein, Susanna Zerbini, Luisa Bastos, and Hans-Gert Kahle
The goal of the Global Velocity Synthesis Working Group (GPSVEL) is to synthesize velocity vectors from international GPS campaigns into a consistent global reference frame. GPSVEL is a new initiative from the University NAVSTAR Consortium (UNAVCO), a U.S. National Science Foundation-funded community-based organization for solid Earth science using GPS. This effort will build on current IAG densification projects of the International GPS Service (IGS) and the International Earth Rotation Service (IERS) Terrestrial Reference System, which incorporates over 200 continuous GPS stations around the world. GPSVEL has since been adopted as the vehicle to achieve the primary goal of the IAG Commission XIV on Crustal Deformation, with commitments already obtained from the IAG Working Group of European Geo-scientists for the Establishment of Networks for Earth-Science Research (WEGENER). IGS analysis centers have since 1995.5 been routinely produce daily estimates of GPS station positions and hence provide a robust global velocity solution. The IGS provides a methodology and standards that are being adapted to the GPSVEL project (e.g., SINEX files with full documentation of a priori constraints and antenna heights). Considerable additional data will be needed, however, because IGS stations are geographically sparse and often not well located to address tectonic issues. As a foundation for GPSVEL, we have used IGS weekly solutions from 1995.5-2001.0 to produce a 5.5-year global velocity solution to which campaign solutions and regional networks will be attached as rigorously as possible. The outcome of this collaborative effort will be a "benchmark" global solution to which geological models such as NUVEL-1A can be compared. GPSVEL will be a primary input into the Global Strain Rate Map Project initiated in 1998 by the International Lithosphere Program. A completed Global Strain Rate Map, determined by combining geodetic data, seismic moment tensors and Quaternary fault slip rates, will provide a large amount of information that is vital for our understanding of continental dynamics and for the quantification of seismic hazards. From the Principal Investigator's perspective, GPSVEL will allow different experiments to be compared in a consistent way, and would make existing solutions more accessible and interpretable to future investigators. GPSVEL will enable Principal Investigators to design their experiments to more fully exploit current data sets. GPSVEL will also provide realistic error scaling based on self-consistency checks in overlapping networks. Towards these goals, commitments are solicited here from Principal Investigators of GPS campaigns and regional permanent networks around the world to achieve truly global coverage towards the development of a product that will have genuine utility to the community. There are several possible things that investigators might be able to contribute (1) GPS data and/or solutions, (2) technical expertise, and (3) the authority to direct any resources that may be necessary to accomplish this task. See http://www.unavco.ucar.edu/science_tech/crustal_motion/ for more information. If you are interested in participating please contact firstname.lastname@example.org with a short note on how you'd like to contribute.