CONTEMPORARY GLOBAL HORIZONTAL CRUSTAL MOTION

An analysis of Satellite Laser Ranging (SLR) data to the LAGEOS satell ite has yielded improved estimates of the horizontal motion for a subs et of 34 tracking sites, within the global tracking network. The analy sis, called SL8.3, utilized data acquired between 1980 January and 199 3 June by the global network composed of 71 sites. The solution design provides for the simultaneous estimation of site positions and their velocities within a pre-defined kinematic frame. The solution is stati stically rigorous and retains the full correlation information content . Least-squares estimates of relative poles of rotation, which are use d to model the motion of one plate relative to another, were made base d on the SLR estimated velocities for sites known to be well away from deformation zones. The resulting SLR-based relative rotation poles di ffer slightly from those of NUVEL-1, but in general, indicate that the magnitude of the SLR implied velocities is slower than those implied by NUVEL-1, consistent with the 4-5 per cent slowing in relative spher ical rates noted in earlier comparisons. Spherical rates between sites in western North America support models of extension in the Basin and Range Province and the rotation of the Sierra Nevada microplate. An a nalysis of the spherical rates crossing the North Atlantic shows that SL8.3 estimated extension between North America-Eurasia sites is gener ally smaller than those implied by NUVEL-1; meanwhile SL8.3 rates betw een North America-Africa sites are in better agreement with NUVEL-1, a lthough they are not so well determined. The maintenance and ongoing m onitoring of global SLR site kinematics provides a well-defined global reference which will aid in combination global kinematic solutions wh ere information from other technologies are merged (e.g. Very Long Bas eline Interferometry and Global Positioning System) and in providing t he context for densification studies of regional kinematics derived fr om terrestrial and Global Positioning System observations.