Single- and multiepoch analyses of global positioning system baseline network: Application to coordinate and velocity determinations in Central Taiwan

Theories and computer programs are developed for single- and multiepoch analyses of a global positioning system ~GPS! baseline network using the datum-free and weighted constraint solutions. Single-epoch analysis is for evaluating data quality, removing outliers, examining network precision, and estimating coordinates. Multiepoch analysis is for simultaneously determining epoch coordi- nates and station velocities. The datum-free solution yields estimable data residuals and relative coordinates and is suitable for adjusting data only and for detecting changes of relative coordinates. The weighted constraint solution allows a lower-order network to be attached to an existing, higher-order network. The analysis methods are applied to a multiepoch GPS baseline network in central Taiwan, which was hit by the 1999 Chi-Chi earthquake measuring 7.3 on the Richter scale. The velocities computed by the methods developed in this study are consistent with those from the Bernese GPS software. The result of the multiepoch analysis indicates that, in the first year after the Chi-Chi earthquake, the crust east of the Chelungpu Fault moved northwestwards at a mean rate of about 10 cm/year, while the crust west of the Chelungpu Fault moved in the opposite direction at a much lower speed.