PLATE MOTION AND CRUSTAL DEFORMATION ESTIMATED WITH GEODETIC DATA FROM THE GLOBAL POSITIONING SYSTEM

We use geodetic data taken over four years with the Global Positioning System (GPS) to estimate (1) motion between six major plates and (2) motion relative to these plates of ten sites in plate boundary zones. The degree of consistency between geodetic velocities and rigid plates requires the (one-dimensional) standard errors in horizontal velociti es to be similar to 2 mm/yr. Each of the 15 angular velocities describ ing motion between plate pairs that we estimate with GPS differs insig nificantly from the corresponding angular velocity in global plate mot ion model NUVEL-1A, which averages motion over the past 3 m.y. The mot ion of the Pacific plate relative to both the Eurasian and North Ameri can plates is observed to be faster than predicted by NUVEL-1A, suppor ting the inference from Very Long Baseline Interferometry (VLBI) that motion of the Pacific plate has sped up over the past few m.y. The Eur asia-North America pole of rotation is estimated to be north of NUVEL- 1A, consistent with the independent hypothesis that the pole has recen tly migrated northward across northeast Asia to near the Lena River de lta. Victoria, which lies above the main thrust at the Cascadia subduc tion zone, moves relative to the interior of the overriding plate at 3 0% of the velocity of the subducting plate, reinforcing the conclusion that the thrust there is locked beneath the continental shelf and slo pe.