Excess Westward Velocities of Minamitorishima (Marcus) and
Kwajalein VLBI Stations from the Expected Velocities Based on
Rigid Motion of the Pacific Plate
by Yasuhiro KOYAMA,
J. Geodetic Soc. Jpn., Vol.42 (1996) pp.43-57
Abstract
All the geodetic Very Long Baseline Interferometry sessions in
which either the Minamitorishima (Marcus) or the Kwajalein station
was involved were reanalyzed to get velocities of these
stations without a constraint from a geologically determined plate
motion model. Velocities of these two stations were obtained
by the least squares estimation on a series of session-by-session
site coordinates in the GLB932 reference frame. Comparison of the
estimated site velocity with an expected site velocity from the
NUVEL-1A plate motion model showed significant difference at each
station. Part of these discrepancies can be reduced if an estimated
Euler vector of the Pacific Plate motion with respect to the North
American Plate is used. However, excess westward velocities of 6
mm/year for Minamitorishima and 10 mm/year for Kwajalein remain.
The position of the Euler pole estimated from Minamitorishima,
Kwajalein, and Kauai site velocities show a good agreement with
the NUVEL-1A Euler pole, whereas the estimated angular velocity
is significantly (~8.9%) faster than that of the NUVEL-1A
model. These results suggest that the Pacific Plate is moving faster
than the NUVEL-1A model with respect to the North American Plate,
and that the rigidity of the Pacific Plate does not hold in a region
around the Minamitorishima and Kwajalein VLBI stations.