Abstract
We analyze 580 continuous GPS stations in California from 5 analysis
centers to quantify the uncertainty in published velocities and develop
a composite velocity for each station. The horizontal positions are
similar but the reported velocity varies by time series algorithm.
Vertical rates for individual stations differ up to 5 mm/yr, with
systematic differences in some areas. The published uncertainties show
variability between analysis centers and are underreported, suggesting
these formal errors do not reflect the true velocity uncertainties.
Differences by a factor of 4 are found in the vertical and is comparable
to deformation rates. An interpolated ensemble vertical velocity field
is developed and regions with the highest rates of uplift or subsidence
correspond to the largest variance in velocities between analysis
centers, but high station density can reduce these uncertainties.
Applications that rely on sub-centimeter GPS accuracy should consider
the inherent uncertainty in published vertical velocity rate estimates.