Satellite laser ranging and geological constraints on plate motion

We have analyzed Satellite Laser Ranging (SLR) observed baseline rates of change and compared them with rates determined from sea floor spreading rates and directions, and earthquake solutions. With the number of years of observation now over six for many of the baselines, the inaccuracy of determining baseline rates of change has diminished so that in some cases it is less than a few mm per year. Thus a direct comparison between baseline rates of change and rates of change established using geophysical information (which we call geological rates) is now feasible. In most cases, there is good agreement between the rates determined from SLR and geological rates, but in some cases there appear to be discrepancies. These discrepancies involve many of the data for which one end of the baseline is either Quincy (California), Huahine (French Polynesia) or Simosato (Japan). We have devised a method for looking at the discrepancies for these SLR observatories which allows us to calculate the motion not modelled by the geologic information. The results are discussed in terms of what is known about plate margins, and other information.