# Removing Land Subsidence Impact from GPS Horizontal Motion in Tianjin, China
## 3 Results
### Horizontal Velocity Field  
The raw horizontal velocity field in the Eurasian framework of the study area and the model-predicted horizontal velocity field with the impact of land subsidence removed are shown in Figure 7. It can be seen that the consistency and overall trend of the predicted horizontal velocity field in the subsidence area of Tianjin with the impact of ground subsidence removed were significantly improved compared with the raw velocity field.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multicolumn{2}{c}{**Horizontal Rate (mm/yr)**} & \multicolumn{3}{c}{**Horizontal Azimuth (\({}^{\circ}\))**} \\  & **Raw** & **Pre** & **Ratio** & **Raw** & **Pre** & **Ratio** \\ \hline MAD & 1.18 & 0.70 & 59.32\% & 20.53 & 14.88 & 72.48\% \\ SD & 1.57 & 0.87 & 55.41\% & 26.95 & 17.29 & 64.16\% \\ CV & 42\% & 24\% & 57.14\% & 136\% & 70\% & 51.47\% \\ \hline \hline \end{tabular} Note: “ratio’ represents the percentage of the predicted value to the original value.  
\end{table}
Table 2: The discrete parameters of the original and predicted values of the horizontal motion of the stations in the subsidence area.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multicolumn{2}{c}{**Horizontal Rate (mm/yr)**} & \multicolumn{3}{c}{**Horizontal Azimuth (\({}^{\circ}\))**} \\  & **Raw** & **Pre** & **Ratio** & **Raw** & **Pre** & **Ratio** \\ \hline MAD & 1.02 & 0.70 & 68.63\% & 12.95 & 9.34 & 72.12\% \\ SD & 1.32 & 0.86 & 65.15\% & 20.28 & 13.06 & 64.40\% \\ CV & 38\% & 25\% & 65.79\% & 95\% & 54\% & 56.84\% \\ \hline \hline \end{tabular} Note: “ratio’ represents the percentage of the predicted value to the original value.  
\end{table}
Table 3: The discrete parameters of the original and predicted values of the horizontal motion of the stations in the study area.  
There are five stations with large differences between the predicted and original horizontal velocities (the difference between the predicted and original rate is more than 1 mm/yr or the difference between the predicted and original azimuthal angle is more than 20\({}^{\circ}\)), all of which are located near the center of the subsidence funnel, but the characteristics of the horizontal motions of these neighboring stations affected by land subsidence are not consistent.  
The differences between the predicted and original velocities at stations WQCG, JHAI, and PANZ are mainly in the rate of motion, while the differences between the predicted and raw velocities at stations NIHE and QING are mainly in the azimuth of motion, suggesting that the mechanism by which land subsidence affects horizontal motion at these stations may not be consistent.  
The predicted horizontal velocities of the stations in the southern region of Tianjin are southward compared with the original horizontal velocities, which indicates that the influence of land subsidence on horizontal motion in the southern region of Tianjin mainly manifests itself in a northward shift. The discrepancy between the predicted and original horizontal velocities of the stations along the eastern coast of Tianjin is minimal, indicating that the horizontal motion of these stations is not significantly influenced by land subsidence. This demonstrates that the impact of land subsidence on GPS horizontal motion varies across different regions within the Tianjin subsidence area.