# Coseismic Stress Change and Viscoelastic Relaxation after the 2008 Great Sichuan Earthquake
## 3 Results  
### Coseismic Coulomb Stress Changes  
Using the optimally oriented fault projection and the parameters shown in Table 2, the distribution of coseismic \(\Delta\)CFS is calculated at the depths of the mainshock epicenters with the four largest aftershocks (Figures 3-7). The coseismic stress changes caused by the Ms 6.3 and Ms 5.8 Kangding earthquakes in 2014 are calculated together and displayed on one map. In Figures 3-7, the evolution of coseismic stress change is systematically tracked, and the triggering effects between the mainshocks and aftershocks are analyzed. Figure 3a shows the coseismic \(\Delta\)CFS pattern induced by the 2008 Wenchuan earthquake. In this figure, the positive lobes are adjacent to the northern and southern ends of the Wenchuan earthquake fault, reflecting the influence of Coulomb stress change (unclamping and clamping effects) and the expected large negative \(\Delta\)CFS (\"shadow\") areas surrounding the eastern and western sides of the fault. Due to the directionality of fault fracture, the areas in front of the fault slip direction are more likely to accumulate larger stress due  
Figure 2: Slip distributions for the source models of **(a)** the 2008 Ms 8.0 great Sichuan (Wenchuan) earthquake ([[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), **(b)** the 2010 Ms 7.1 Yushu earthquake [21], **(c)** the 2013 Ms 7.0 Lushan earthquake [67], **(d)** the 2014 Ms 6.3 Kangding earthquake [19], **(e)** the 2014 Ms 5.8 Kangding earthquake [19], and **(f)** the 2017 Ms 7.0 Jüuzhaigou earthquake [68]. to the pushing effect (positive lobes in Figure 3a). Figure 3a also shows the correlation between the stress change distribution and the subsequent earthquakes. Figure 3b,c shows the temporal distribution of aftershocks, indicating that the subsequent seismicity was obviously affected by the main earthquake. In the first month after the mainshock, many events occurred, primarily at sites along the ruptured fault, including some events with M \(\geq\) 6.0. After more than a month, the frequency of aftershocks was still very high. We noted that only in the areas outside the main rupture, there is a relation between aftershocks and stress-enhanced areas (Figure 3a). In summary, Figure 3 suggests a potential correlation between most of the shocks distributed in areas with an increase in coseismic stress. Similarly, Figures 4-7 show the coseismic stress change field due to the 2010 Yushu earthquake, the 2013 Lushan earthquake, the two 2014 Kangding earthquakes, and the 2017 Ms 7.0 Jiuzhaigou earthquake. These figures also display the correlation between the stress change distribution and the aftershocks. The correlations between the \(\Delta\)CFS and the aftershocks support the idea that the coseismic stress changes caused by the six earthquakes had a fundamental impact on the subsequent earthquakes in a short time following the main events. Figure 5: (**a**) Distribution of coseismic Coulomb failure stress changes caused by the 2013 Ms 7.0 Lushan earthquake at the depth of the mainshock and aftershocks ([PERSON] et al. [5]). (**b**) Temporal distribution of aftershock magnitudes. (**c**) Cumulative number of aftershocks over time. Figure 6: (**a**) Distribution of coseismic Coulomb failure stress changes caused by the 2014 Ms 6.3 and Ms 5.8 Kangding double earthquakes at the depth of the mainshock and aftershocks ([PERSON] et al. [74]). (**b**) Temporal distribution of aftershock magnitudes. (**c**) Cumulative number of aftershocks over time. Figure 7: (**a**) Distribution of coseismic Coulomb failure stress changes caused by the 2017 Ms 7.0 Jiuzhaigou earthquake at the depth of the mainshock and aftershocks ([PERSON] et al. [22]). (**b**) Temporal distribution of aftershock magnitudes.