# Monitoring of Possible Activities of Yangsan Fault Zone Using GNSS
## 4 Results--Discussion
### Time Series
#### 4.1.3 Stress and Strain Analysis
Figure 7: (**a**) Stress strain of the triangular network in 2018–2019; (**b**) stress strain of the triangular network in 2020–2021. The red triangle represents the epicenter of the earthquake that occurred on 12 September 2016. \begin{table}
\begin{tabular}{|c|c|c|c|c|c|c|c|c|c|} \hline \multirow{2}{*}{**num**} & \multicolumn{2}{c|}{**Period**} & \multicolumn{2}{c|}{**17 July 2018–31 December 2019**} & \multicolumn{2}{c|}{**1 January 2020–31 December 2021**} \\ \cline{2-11}  & \ \begin{tabular}{c} **Triangular** \\ **Network** \\ \end{tabular}  & \(E_{1}\) (**nstr**) & \(E_{2}\) & \(Y\) & \(\Delta\) & \(E_{1}\) & \(E_{2}\) & \(Y\) & \(\Delta\) \\  & **Network** & **(nstr)** & **(nstr)** & **(nstr)** & **(nstr)** & **(nstr)** & **(nstr)** & **(nstr)** \\ \hline \multirow{10}{*}{1} & \multirow{5}{*}{
\begin{tabular}{c} CH  
\begin{table}
\begin{tabular}{|c|c|c|c|c|c|c|c|c|c|} \hline \multirow{2}{*}{**num**} & \multicolumn{2}{c|}{**Period**} & \multicolumn{2}{c|}{**17 July 2018–31 December 2019**} & \multicolumn{4}{c|}{**1 January 2020–31 December 2021**} \\ \cline{2-11}  & \ \begin{tabular}{c} **Triangular** \\ **Network** \\ \end{tabular}  & \(E_{1}\) **(Instr)** & \(E_{2}\) **(Instr)** & \(Y\) **(Instr)** & \(\Delta\) **(Instr)** & \(E_{1}\) **(Instr)** & \(E_{2}\) **(Instr)** & \(Y\) **(Instr)** & \(\Delta\) **(Instr)** \\ \hline \multirow{4}{*}{4} & \multirow{4}{*}{ \begin{tabular}{c} BOGG- \\ CGUG- \\ HDBG \\ \end{tabular}  } & \(85.88\) & \(-85.75\) & \(171.63\) & \(0.12\) & \(-3.01\) & \(-73.17\) & \(70.16\) & \(-76.18\) \\ \cline{2-11}  & & \multicolumn{4}{c|}{Strain ellipse (tagged by 1 ed)} & \multicolumn{4}{c|}{Strain ellipse (tagged by 1 ed)} \\ \cline{2  
\begin{table}
\begin{tabular}{|c|c|c|c|c|c|c|c|c|c|} \hline \multirow{2}{*}{**num**} & \multicolumn{2}{c|}{**Period**} & \multicolumn{2}{c|}{**17 July 2018–31 December 2019**} & \multicolumn{2}{c|}{**1 January 2020–31 December 2021**} \\ \cline{2-11}  & \ \begin{tabular}{c} **Triangular** \\ **Network** \\ \end{tabular}  & \(E_{1}\) **(Instr)** & \(E_{2}\) **(Instr)** & \(Y\) **(Instr)** & \(\Delta\) **(Instr)** & \(E_{1}\) **(Instr)** & \(E_{2}\) **(Instr)** & \(Y\) **(Instr)** & \(\Delta\) **(Instr)** \\ \hline \multirow{6}{*}{7} & \multirow{6}{*}{GCNG-POSG-TEGN} & \multirow{6}{*}{
\begin{tabular}{c} GCNG-POSG-TEGN \\ \end{tabularThe triangular network with Cheongun (CGUG), Deokcheon (DUCG), and Bonggye (BOGG) as vertices has the maximum area strain, and an earthquake occurred in the CGUG-DUCG-GCNG triangle. In this study we computed a daily baseline between each station in the area with the largest stress strain and close to the earthquake epicenter. The rate of change in the baseline distance was calculated using the processed time series. Figure 8 shows the baseline change rate between stations based on the daily time series. As a result, the rate of change is negligible in its magnitude, reaching about \(\pm 2\) mm in the range with no significant bias. From these results, it seems that there was no evident displacement or deformation in the surrounding area where the earthquake occurred.