[1] The total zenith tropospheric delay (ZTD) is an important parameter of the atmosphere and directly or indirectly reflects the weather and climate processes and variations. In this paper the ZTD time series with a 2-hour resolution are derived from globally distributed 150 International GPS Service (IGS) stations (1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006), which are used to investigate the secular trend and seasonal variation of ZTD as well as its implications in climate. The mean secular ZTD variation trend is about 1.5 ± 0.001 mm/yr at all IGS stations. The secular variations are systematically increasing in most parts of the Northern Hemisphere and decreasing in most parts of the Southern Hemisphere. Furthermore, the ZTD trends are almost symmetrically decreasing with increasing altitude, while the summation of upward and downward trends at globally distributed GPS sites is almost zero, possibly reflecting that the secular ZTD variation is in balance at a global scale. Significant annual variations of ZTD are found over all GPS stations with the amplitude from 25 to 75 mm. The annual variation amplitudes of ZTD near oceanic coasts are generally larger than in the continental inland. Larger amplitudes of annual ZTD variation are mostly found at middle latitudes (near 20°S and 40°N) and smaller amplitudes of annual ZTD variation are located at higher latitudes (e.g., Antarctic) and the equator areas. The phase of annual ZTD variation is about 60°in the Southern Hemisphere (about February, summer) and about 240°in the Northern Hemisphere (about August, summer). The mean amplitude of semiannual ZTD variations is about 10 mm, much smaller than annual variations. The semiannual amplitudes are larger in the Northern Hemisphere than in the Southern Hemisphere, indicating that the semiannual variation amplitudes of ZTD in the Southern Hemisphere are not significant. In addition, the higher-frequency variability (RMS of ZTD residuals) ranges from 15 to 65 mm of delay, depending on altitude of the station. Inland stations tend to have lower variability and sites at ocean and coasts have higher variability. These seasonal ZTD cycles are due mainly to the wet component variations (ZWD).

The plate tectonics of Northeast Asia are very complex with diffuse and sparse seismicity in the broad plate deformation zones embedded by a number of micro-plates, particularly the controversial Amurian plate. Now the increasingly dense GPS networks in this area provide an important tool to investigate plate tectonic kinematics and to identify the approximate plate tectonic geometries. In this paper, we have processed GPS data (1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005) collected by an extensive GPS network (China and South Korea) with more than 85 continuous sites and about 1000 campaign GPS stations. The kinematics of Northeast Asia is studied by modeling GPS-derived velocities with rigid block rotations and elastic deformation. We find that the deformation in Northeast Asia can be well described by a number of rotating blocks, which are independent of the Eurasian plate motion with statistical significance above the 99% confidence level. The tectonic boundary between the North China and Amuria plates is the Yin Shan-Yan Shan Mountain belts with about 2.4 mm/yr extension. Along the boundary between North China and South China, the Qinling-Dabie fault is moving left laterally at about 3.1 mm/yr. The Amuria and South Korea blocks are extending at about 1.8 mm/yr. The Baikal Rift between the Amurian and Eurasian plates is spreading at about 3.0 mm/yr. The 9-17 mm/yr relative motion between the Amuria and Okhotsk blocks is accommodated at the East Sea-Japan trench zone. Localized deformation near the Qinling-Dabie fault and Yin Shan-Yan Shan Mountain belts may be elastic strain accumulation due to interseismic locking of faults.

The results of GPS positioning depend on both functional and stochastic models. In most of the current GPS processing programs, however, the stochastic model that describes the statistical properties of GPS observations is usually assumed that all GPS measurements have the same accuracy and are statistically independent. Such assumptions are unrealistic. Although there were only a few studies modeling the effects on the GPS relative positioning, they are restricted to short baselines and short session lengths. In this paper, the stochastic modeling for IGS long-baseline positioning (with 24-hour session) is analyzed in the GAMIT software by modified stochastic models. Results show that any mis-specifications of stochastic model result in unreliable GPS baseline results, and the deviation of baseline estimations reaches as much as 2 cm in the height component. Using the stochastic model of satellite elevation angle-based cosine function, the precision of GPS baseline estimations can be improved, and the GPS baseline component is closest to the reference values, especially GPS height.

were analyzed to quantitatively investigate the plate deformation patterns and distributions in the South Korean peninsula. The results show two anomalous rates of strain accumulation in South Korea, a W-E compression accumulation of crustal strain in the East and West parts, and a N-S extension strain accumulation in the middle part along the longitude of about 127.5• E. In addition, the GPS-derived seismic moment accumulation rate is significant and consistent with recent historic earthquakes and fault zones in South Korea. The most anomalous seismic moment rates are in the middle part (about 127.3• E, 35.5• N), North edge (about 128.0 • E, 38.0• N) and Northeast part (about 128.5• E, 37.3• N) of South Korea, indicating a high earthquake risk.

Analysis of continuous GPS data [2000][2001][2002][2003] at 50 stations of the Korean GPS Network (KGN) suggests that the southern part of the Korean peninsula is tectonically more stable than other regions in the Eastern Asia. The average velocity was ∼1.5 mm/yr and the average overall strain rate was around −0.3 × 10 −9 str/yr. The obtained velocity field indicates the presence of anticlockwise rotation of the whole region with respect to Daejeon station (DAEJ), in the central part of South Korea. It also showed that KM-OB (Kyonggi Massif and the Okchon Basin) and YM-TB (Yeongnam Massif and Taebaeksan Basin) have left-lateral shearing movements. Both movements were confirmed by the deformation analysis of the KGN horizontal velocity field using the infinitesimal plate theory. The results show that South Korea moves toward the WNW direction with a velocity of 0.9 mm/yr with a slow anticlockwise rotation. The strain field in South Korea indicates the existence of both compression and tension. The compression and extension axes have WSW-EWE and NNW-SSE directions, respectively.