## 4 Results and Analysis
### Evolution of Images of Aftershock Activity Depicted by Focal Depth  
Spatial scanning was performed using events with depth data in the catalog, i.e., at a step size of 0.1\({}^{\circ}\) for both longitude and latitude. For all earthquakes in each 0.1\({}^{\circ}\)\(\times\) 0.1\({}^{\circ}\) grid point, the average depth was used as the depth value of the grid point, and then kriging interpolation was applied to all the grids. We counted at least ten events in each grid node in the Wenchuan aftershock zone as samples (as well as five events for the Lushan aftershock zone) to prevent the average depth of grid points from being affected by too few events. The contour lines of depth distribution at different periods after the mainshock were obtained and superimposed with regional faults (Figures 6 and 7).  
To illustrate the evolution of the deep seismogenic environment in the Wenchuan aftershock zone. Figure 6 shows the spatial evolution of the aftershock depth at one day, one week, one month, six months, one year, and three years after the mainshock. The analysis shows that the focal depth of the Wenchuan aftershock zone spread along the direction of the fault. With Mianyang as the boundary, the aftershock zone can be divided into the southern section and the northern section. The depth distribution is generally deep in the southeast and shallow in the northwest, and the average aftershock focal depth is 10-15 km.  
A comparison of the aftershock activity images depicted by the focal depth information shown in Figure 6d,e revealed that the image formed one year after the mainshock did not show a significantly different pattern in the following two years. This finding indicates that after the mainshock, the aftershock frequency tends to be stable one year later, which means that the active aftershock period of the Wenchuan \(M_{S}\) 8.0 was less than one year.  
Figure 7 shows the spatial evolution of aftershock depths at one day, one week, five months, ten months, one year and three years after the mainshock in the Lushan aftershock zone. The analysis shows that the focal depths of the Lushan aftershock are distributed around the fault, with the fault as the boundary, with a trend of deep in the southeast and shallow in the northwest. Moreover, a comparison of the regional aftershock activity images depicted by the focal depth information in Figure 7d,e revealed that the pattern of the image formed ten months after the mainshock presented limited changes in the following one year, which indicates that the aftershock frequency tended to be stable ten months after the Lushan mainshock. Therefore, the active aftershock period of the Lushan \(M_{S}\) 7.0 earthquake was less than ten months.  
\begin{table}
\begin{tabular}{c c c} \hline
**Windows** & **AAIC** & \(\mathbf{P_{b}}\) \\ \hline \(W_{1}\) and \(W_{2}\) & 2.6 & 0.03 \\ \(W_{2}\) and \(W_{3}\) & 9.9 & \(9.5\times 10^{-4}\) \\ \(W_{1}\) and \(W_{3}\) & 28.9 & \(7.1\times 10^{-8}\) \\ \(L_{1}\) and \(L_{2}\) & 2.6 & 0.03 \\ \(L_{2}\) and \(L_{3}\) & 4.6 & 0.01 \\ \(L_{1}\) and \(L_{3}\) & 20 & \(5.9\times 10^{-6}\) \\ \hline \end{tabular}
\end{table}
Table 1: Results of the \(P\) parameter test between windows.  
Figure 6: Spatial distribution of the focal depths of the aftershocks following the Wenchuan \(M_{\rm S}\) 8.0 earthquake on the fault plane. Red lines represent the locations of faults. (**a**) One day after the mainshock; (**b**) 1 week after the mainshock; (**c**) 1 month after the mainshock; (**d**) 1 year after the mainshock; and (**e**) 3 years after the mainshock.  
Figure 7: Spatial distribution of the focal depths of the aftershocks following the Lushan \(M_{\rm S}\) 7.0 earthquake on the fault plane. Red lines represent the locations of faults. (**a**) One day after the mainshock; (**b**) 1 month after the mainshock; (**c**) 5 months after the mainshock; (**d**) 10 months after the mainshock; and (**e**) 2 years after the mainshock.