At both stations, the pre-2005 height coordinates were then
analyzed for the linear trends which represent inter-seismic uplifts. In
the determination of these motions, we opted for ordinary regression
instead of IRLS, which was used in other trend analyses in this study.
This is because the IRLS technique requires a substantial number of
observations to be able to interpret where the trend line lies for the
majority. A limited number of GPS measurements in this case does not
provide this consensus information. Ordinary weighted least square
regression was therefore applied to obtain pre-earthquake vertical
motion which is the sum of GIA and inter-seismic deformation.
Observations having residuals greater than 2-sigma from the residual
mean are considered outliers and all observations pass the criteria.
The detected uplift rates are 3.8±1.3 mm/yr at CHON and 2.2±
0.8 mm/yr at BANH. The uncertainties in vertical velocities were
obtained by increasing the formal errors of the velocity estimates by
individual factors determined from the weighted root mean square
(WRMS) that represents the actual scatter in each time series and
the total observation period (T) using the 2WRMS/T algorithm as
discussed in Simons et al. (2007).