We tested the sensitivity of the pre-2005 vertical motions by
recursively removing from the time series one pre-earthquake
measurement at a time and re-fitting the linear trend to the rest. At
both CHON and BANH, removing any single measurement from the
height time series of BANH does not corrupt the uplift trend. Further,
the BANH height time series is very consistent with that of CHON. If measurements in Nov-1998 and Oct-2000, are removed from CHON
time series, its up–down pattern is the same as depicted by that of
BANH. This similarity is not repeated after the earthquake, when nonsteady
motion is expected even though measurements and processing
were carried out in the same fashion as in the pre-earthquake period.
This suggests that the pre-2005 similarity between CHON and BANH
did not result from any systematic effects of GPS, but rather from the
tectonic signal. Altogether, this confirms the presence of preearthquake
uplift that was captured by GPS despite the noisy
appearance of the data