GEODVEL: Plate Angular Velocities from Four Space Techniques

Comparisons of rates from geodesy (over decades), from moment release in historical earthquakes (centuries), and fault slip rates from paleoseismology (kyr) begin with the premise that the plates are moving steadily at the velocity they have moved for intervals of at least thousands of year. In this study we compare geodetic estimates of plate angular velocities from observations 4 space techniques (GPS, VLBI, SLR, and DORIS) with estimates of plate angular velocities over geologic time determined from transform fault azimuths and spreading rates from magnetic anomalies over 0.8 to 3 million-year-old seafloor. A shortcoming of prior geodetic plate motion models is that they depend on the velocity of Earth's center (and a realization of the International Terrestrial Reference Frame (ITRF)). That the velocity of Earth's center is uncertain is evident in the substantial (2 mm/year) difference in the last two realization of the ITRF. In the GEODVEL (GEODetic VELocity) set of angular velocities, we determine plate velocities that are less subject to errors in the estimate of the velocity of Earth's center, and we determine uncertainties in plate velocities that account for the uncertainty in the velocity of Earth's center. Similarities and differences between geodetic and geologic angular velocities will be discussed.