Common-mode Signals Observed from the Korean GPS Network

As of September 2003, there are more than 70 permanent Global Positioning System (GPS) stations in South Korea. We have been observing the three-dimensional velocity of each site for geodynamical studies in the northeast Asia. From the time series of the estimated site positions, most of which are longer than three years now, we found very interesting common-mode signals. Especially, in the vertical direction, the amplitude of the seasonal (annual) signal reaches up to a few centimeters. Other than the seasonal signal, we also could observe very intriguing dips and peaks occurring randomly. In this discussion, we will first introduce the current Korean GPS Network and will show two different ways to get the common-mode signals from a set of time series. By trying out many different data processing schemes, we will infer the best candidates for the real cause for those common-mode signals.