## 3 Results and Discussion
### Earthquake Displacement
#### 3.2.2 Dynamic Deformation of Lushan Earthquake  
The Mw7.0 Lushan earthquake, which occurred at 00:02:46 on 20 April 2013, caused significant ground motions. Even about 5 cm deformations could be detected at distances of 42 km from the epicenter. Lushan county is located at the front edge of the southern section of the Longmenshan fault zone, which is part of the eastern edge of the Tibetan Plateau, where earthquakes occur frequently. In this research, 1 Hz GPS data of continuous sites of CMONOC during the 2013 Lushan earthquake are adopted to calculate the coseismic deformation and ionospheric anomalous distribution. Eight CMONOC stations near the  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**RMS (cm)**} \\ \cline{2-7}
**Site** & \multicolumn{2}{c}{**North**} & \multicolumn{2}{c}{**East**} & \multicolumn{2}{c}{**Up**} \\ \cline{2-7}  & **TRACK** & **SF PPP** & **TRACK** & **SF PPP** & **TRACK** & **SF PPP** \\ \hline
0029 & 2.67 & 48.88 & 1.14 & 23.48 & 3.98 & 58.97 \\
0033 & 3.12 & 50.88 & 0.87 & 18.01 & 3.90 & 53.69 \\
0167 & 1.95 & 57.61 & 1.03 & 4  
epicenter (as listed in Table 3) are chosen to analyze the surface deformation. The detailed information of the selected GPS stations is shown in Table 3. The corresponding geospatial distribution of those selected stations and the spatial geometry between the epicenter and those selected stations are presented in Figure 5.  
Here, we provide the dynamic displacement of the first 10 min on 20 April (UTC time) that are calculated by GPS data before, during, and after the earthquake. The solutions calculated by GAMIT/TRACK are plotted in Figure 6, from which we can see that the deformation engendered by the Lushan earthquake is significant at only the SCTQ station but rather slight at the other stations. The reason is that SCTQ is the nearest station to the earthquake epicenter with a distance of about 42 km, while the other stations are more than 110 km even up to 230 km away, which can be found in Table 3 and Figure 5. The deformations at the SCTQ station, which are calculated by GAMIT/TRACK and SF-PPP, are shown in detail in Figure 7.  
To evaluate the accuracy of our method, the solutions from GNSS data products of the China Earthquake Administration ([[http://www.cgps.ac.cn](http://www.cgps.ac.cn)]([http://www.cgps.ac.cn](http://www.cgps.ac.cn)), accessed on 27 August 2019) are adopted as the reference. According to the comparison results, it can be known that both GAMIT/TRACK and SF-PPP can record the coseismic deformation, with the deformation of about 4-5 cm in the north and about 2-3 cm in the east. However, as shown in Figure 7, the solutions from GAMIT/TRACK are more stable than those of SF-PPP. It may be because the solution of such SF-PPP model depends highly on the accuracy of virtual observation of ionospheric delay, the accuracy of pseudorange, and the estimation strength of ambiguities and ionospheric delay. The measurement accuracy of pseudorange is empirically about 0.3 m. Since the GIM data are utilized as virtual observation of ionospheric delay, and the accuracy for GIM data is about 2-8 TECU [53], the accuracy of the ionospheric delay virtual observation is around 0.33-1.32 m errors. Compared with the conventional SF-PPP, the proposed SF-PPP model has more parameters, which may weaken the positioning solutions. On the other hand, as is proven by [PERSON] et al. [41], such a proposed SF-PPP model can reduce the position solutions noise obviously. Thus, it is possible to use its position solutions to identify the surface deformation during  
Figure 6: Time series for the three directions of selected stations from GAMIT/TRACK after 00:00:00 (UTC time); the black dotted line stands for the time of earthquake occurred. Figure 7: Time series for the three directions of SCTQ station after 00:00:00 (UTC time), respectively; the black dotted line stands for the time of earthquake occurred. the earthquake. What is more, the proposed SF-PPP model can also provide the ionospheric VTEC distribution.