# An Analysis of the 2008 \(M_{\rm s}\) 8.0 Wenchuan Earthquake's Aftershock Activity
## 6 Conclusions  
In this study, we thoroughly investigated the Wenchuan aftershock activity, and our conclusions are as follows:  
According to the G-R equation (Wenchuan, 2018), \(M_{c}\) was found to have a magnitude of 2.5, and the \(b\)-value of the Wenchuan aftershock sequence was calculated to be 0.89 \(\pm\) 0.02, which is relatively small. The small \(b\)-value may have been caused by the absence of small earthquakes in the catalog. In addition, the physical properties of the media in the earthquake area are factors that could have led to the small \(b\)-value. According to the modified [PERSON] law ([PERSON], 1963; [PERSON], 1963), the pattern of decay in the Wenchuan aftershocks was studied, and the \(p\)- and \(c\)-values obtained were 1.05 \(\pm\) 0.02 and 3.00, respectively. We found that the Wenchuan aftershock sequence conforms well to the Omori formula. The \(p\)-value varied little with \(M_{\text{min}}\), whereas the \(c\)-value drastically varied with the change in \(M_{\text{min}}\). The absence of the aftershock records in the first few hours after the mainshock and the complexity of the source rupture process were responsible for the large \(c\)-value. The \(b\)-value spatially varied from 0.6 to 1.2 in the aftershock zone (Figure 6) and was generally small. The areas with relatively large \(b\)-values (\(b>\) 0.9) were mainly located near the mainshock epicenter and in the central and northeastern parts of the aftershock zone. The areas with relatively small \(b\)-values (\(b\leq\) 0.9) were located in the southwestern part of the aftershock zone. The relatively large \(b\)-values in the northeastern part of the aftershock zone may have been caused by the fault ruptures in this area that were newly generated during the earthquake. The rupture mechanism was relatively simple, and the fault planes were relatively smooth, which was favorable for rapid stress adjustments. As a result, although the aftershocks were dense in this area, their intensity was low, ultimately leading to the large \(b\)-value. In the southwestern part of the aftershock zone, the aftershock intensity was relatively high because of the complex rupture mechanism, and the \(b\)-value was generally small. In addition, several strong aftershocks occurred in the southwest area of Wenchuan and at the northeast end of the aftershock zone, where the \(b\)-value was the smallest. The subsurface anomalies in these two areas may have impeded the rupture and slip of faults, leading to the occurrence of strong aftershocks and the small \(b\)-value. The \(p\)-value spatially varied mainly between 0.6 and 1.8 (Figure 7), which is a large variation range, indicating the spatial heterogeneity of the aftershock decay. A large \(p\)-value indicates the rapid decay of aftershock activity. The areas with high \(p\)-values (\(p\geq\) 1.2) were mainly distributed in the aftershock area along the Longmenshan central fault, spreading northeast from the mainshock epicenter. Moreover, the distribution of areas with large \(p\)-values is consistent with the projection of shallow parts of the faults on the ground. The reason for this may be that in the shallow part of the fault plane, the fault rupture mechanism was simpler than that in the deep part, the fault plane was relatively smooth,and the stress adjustments were rapid. As a result, the aftershock activity quickly decayed, and the \(p\)-value was relatively large. The spatial variations in the \(b\)- and \(p\)-values were related to the earthquake source mechanism and the physical properties of the rock media. We compared the spatial distribution of the calculated \(b\)-values (Figure 6) and \(p\)-values (Figure 7) with other results for the Wenchuan earthquake [25; 26; 27; 30; 31] and found that the spatial variation in the \(b\)-value may have been related to the \(P\)-wave velocity, density of the media, and the stress change in the earthquake area.