# Coseismic Stress Change and Viscoelastic Relaxation after the 2008 Great Sichuan Earthquake
## 2 Method and Models
### Slip Source Model of Earthquakes  
To calculate the stress evolution caused by these earthquakes since 2008, several variable slip source models are tested from different data sets by estimating the correlation between Coulomb stress changes and aftershocks. Figure 2 shows the slip distributions of these six models. Other parameters are listed in Table 3.  
Figure 2a shows the 2D slip model of the 2008 Ms 8.0 Wenchuan earthquake. The fault plane is set to a length of 318 km and a width of 22 km, with a strike of 229\({}^{\circ}\), and it is discretized as a set of 168 patches (elements) with dimensions of 21 \(\times\) 8 km\({}^{2}\) ([[http://www.geol.ucsb.edu/faculty/ji/big_earthquakes/2008/05/12/ShiChuan.html](http://www.geol.ucsb.edu/faculty/ji/big_earthquakes/2008/05/12/ShiChuan.html)]([http://www.geol.ucsb.edu/faculty/ji/big_earthquakes/2008/05/12/ShiChuan.html](http://www.geol.ucsb.edu/faculty/ji/big_earthquakes/2008/05/12/ShiChuan.html)), accessed on 1 January 2016). Figure 2b shows the 2D slip model of the 2010 Ms 7.1 Yushu earthquake. The fault plane is set to a length of 96 km and a width of 30 km, with a strike of 119\({}^{\circ}\), and it is discretized as a set of 32 \(\times\) 10 elements with dimensions of 3 \(\times\) 3 km\({}^{2}\)[21]. Figure 2c shows the 2D slip model of the 2013 Ms 7.0 Lushan earthquake. The fault plane is set to a length of 63 km and a width of 48 km, with a strike of 219\({}^{\circ}\), and it is discretized as a set of 21 \(\times\) 16 elements with dimensions of 3 \(\times\) 3 km\({}^{2}\)[67]. Figure 2d,e shows the 2D slip models of the 2014 Ms 6.3 and Ms 5.8 Kangding double earthquakes. In Figure 2d, the fault plane of the Ms 6.3 event is set to a length of 46 km and a width of 21 km, with a strike of 330\({}^{\circ}\), and it is discretized as 46 \(\times\) 21 elements with dimensions of 1 \(\times\) 1 km\({}^{2}\)[19]. In Figure 2e, the fault plane of the Ms 5.8 event is set to a length of 21 km and a width of 22 km, with a strike of 153\({}^{\circ}\), and it is discretized as 21 \(\times\) 22 elements with dimensions of 1 \(\times\) 1 km\({}^{2}\)[19]. Figure 2f shows the 2D slip model of the 2017 Ms 7.0 Jiuzhaigou earthquake. The fault plane is set to a length of 32 km and a width of 30 km, with a strike of 153\({}^{\circ}\), and it is discretized as 16 \(\times\) 15 elements with dimensions of 2 \(\times\) 2 km\({}^{2}\)[68]. The boundary condition of our 2D models generated using the finite element method (e.g., [69; 70; 71]) follows the multilayered viscoelastic half-space model setting (e.g., [60]).  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Earthquake**} & \multirow{2}{*}{**Year**} & \multirow{2}{*}{**Depth**} & \multicolumn{2}{c}{**Epicenter**} & \multicolumn{2}{c}{**Rupture Plane**} & \multirow{2}{*}{**Length**} & \multirow{2}{*}{**Width** (km)**} \\ \cline{3-3} \cline{5-8}  & & & **Latitude (\({}^{\circ}\))** & & & **Longitude (\({}^{\circ}\))** & & **Strike (\({}^{\circ}\))** & **Dip (\({}^{\circ}\))** & **(km)** & **(km)** \\ \hline Wenchuan & 2008 & 10.0 & 31.10 & 103.30 & 229 & 33 & 318 & 22 \\ Yushu & 2010 & 14.0 & 33.20 & 96.60 & 119 & 83 & 96 & 30 \\ Lushan & 2013 & 12.3 & 30.28 & 102.96 & 219 & 33 & 63 & 48 \\ Kangding Ms 6.3 & 2014 & 20.0 & 30.30 & 101.80 & 330 & 84 & 46 & 21 \\ Kangding Ms 5.8 & 2014 & 16.0 & 30.20 & 101.75 & 153 & 68 & 21 & 22 \\ Jiuzhaigou & 2017 & 11.0 & 33.20 & 103.82 & 153 & 84 & 32 & 30 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Earthquake parameters for the six source models. The epicenters of the 2008 Ms 8.0 Wenchuan earthquake and the 2013 Ms 7.0 Lushan earthquake are from the USGS. The epicenters of the 2010 Ms 7.1 Yushu earthquake, the 2014 Ms 6.3, Ms 5.8 Kangding double earthquakes, and the 2017 Ms 7.0 Jiuzhaigou earthquake are from the China Earthquake Networks Center (CENC). Other parameters are from the source models shown in Figure 2.