# An Analysis of the 2008 \(M_{\rm s}\) 8.0 Wenchuan Earthquake's Aftershock Activity
## 5 Discussion
The spatial distribution of areas with large \(p\)-values is consistent with the fault slip distribution pattern obtained by [PERSON] et al. [26], especially in Yingxiu-Hanwang, Beichuan, and Qingchuan, which are areas with a concentrated fault slip, and the \(p\)-value linearly correlated with the amount of fault slip. In addition, we found that the \(b\)- and \(p\)-values were both large in the Qingchuan area, and [PERSON] and [PERSON] [14] suggested that special geotectonic conditions (e.g., the Holocene alluvial sedimentary structure) may lead to increases in the \(b\)- and \(p\)-values. Therefore, we inferred that special geotectonic structures may be present in the vicinity of Qingchuan. [PERSON] et al. [27] calculated the changes in the stress in the earthquake area after the Wenchuan mainshock, finding that the stress increased at the intersection of the Longmenshan fault and the Sichuan Basin. Coulomb stress substantially increased in the south of the mainshock fault, and the stress in the Qingchuan and Huya areas decreased. This pattern shows a correlation with the spatial distribution of the \(b\)-value that we calculated. As described in Section 3, the \(b\)-value was generally small in the earthquake area along the Longmenshan front fault (i.e., the area intersecting the Sichuan Basin) and the southwestern part of the aftershock area, and the \(b\)-value was the largest in the Qingchuan area, indicating that areas with large and small \(b\)-values may correspond to the regions experiencing small and large stresses, respectively. However, no information is available on the decreases or increases in stress in the areas around the mainshock epicenter, where the \(b\)-value was large, and at the northeast end of the aftershock area, where the \(b\)-value was the smallest. Based on the above results, we speculate that the stress decreased and increased in these areas, respectively. Moreover, these two areas are located near the starting and end points of the mainshock rupture, so we speculate that subsurface anomalies may exist in these two areas. [PERSON] et al. [28] found that the variations in \(b\)-values agree with friction-related seismic velocity perturbations and stated that the regions with high and low \(b\)-values correspond to relatively low and high \(P\)-wave velocities, respectively. In addition, [PERSON] and [PERSON] [29] also demonstrated that a region with high seismic wave velocity may be a region that is subjected to high stress. [PERSON] et al. [30] studied the three-dimensional \(P\)-wave velocity structure in and around the Wenchuan earthquake area. Their results showed widespread high-velocity anomalies at a depth within 20 km of the surface in the crust along the Longmenshan fault, which is consistent with the typically small \(b\)-values in the aftershock zone revealed in our study. By comparing the spatial distribution of the \(b\)-value calculated in this study with the distribution of three-dimensional \(P\)-wave velocity anomalies reported by [PERSON] et al. (2019), we found that low \(P\)-wave velocity anomalies appeared in areas with large \(b\)-values, with high-velocity anomalies being found in the areas with small \(b\)-values, especially at the northeast end of the aftershock zone, where the high-velocity anomalies along the Ningqiang-Mianxian region (Ningqiang and Mianxian, 2020) may have been responsible for the small \(b\)-values. In addition, we compared the spatial distribution of the \(b\)-value with the apparent velocity structure in the Longmenshan fault zone and its surroundings calculated by [PERSON] et al. (2019). We found that the apparent velocities were relatively high in the areas with small \(b\)-values and relatively low in the areas with large \(b\)-values. The above findings show that the spatial distribution of the \(b\)-value in the aftershock region is closely related to the properties of the media in the earthquake area.