## 6 Discussion  
The occurrence of the Luding earthquake was inevitable, whether considering the historical seismic recurrence cycle or the high deformation-locking area. Since 1400, 23 \(M_{\rm S}\)\(\geq\) 6.5 earthquakes have been recorded in the study region, and the rupture zones almost cover the entire boundary fault (Figure 10). Since the 21 st century, there have been two \(M_{\rm S}\)\(\geq\) 6.0 earthquakes on the Xianshui He fault belt, namely, the Kangding \(M_{\rm S}\) 6.3 in 2014 [76] and the Luding 6.8 in 2022 [77]. The section from Kangding (KD) to Shimian (SM) is located in the historic rupture zone of the Kangding south \(M_{\rm S}\) 734 in 1786; the epicenter of the Luding \(M_{\rm S}\) 6.8 earthquake is located at the southern end of the historic rupture zone [35]. The Xianshuihe Fault Zone, as one of the fault zones with the most frequent strong seismic activity, has a significant segmented seismic recurrence cycle. The Moxi section where the Luding \(M_{\rm S}\) 6.8 earthquake is located has a characteristic seismic recurrence cycle of  
Figure 9: The G–R relationship fitting diagram. The red dots indicate the cumulative frequencies of \(M_{L}\geq\) 2.0 events in the period of 2010–2013 with a \(b\)-value of 1.18, while the blue dots mark the same physical quantities in the period of 2018–2021 with a \(b\)-value of 0.91. The solid lines are the fit lines for different periods. 155 years [50]. Before the Luding \(M_{S}\) 6.8 earthquake, the 236-year elapsed time had already passed far beyond the recurrence period. [PERSON] et al. [78] explained this inevitability from another perspective. They used the DEFNODE algorithm [79] to invert the fault locking of the Xianshui He fault belt based on GNSS data from 2016 to 2020. The results showed that the Luding \(M_{S}\) 6.8 earthquake sequence was located in the high-locking region of the southern section of the Xianshui He fault belt (PHI close to 1, Figure 11), indicating that the Luding seismic source area was in a state of stress accumulation during this period. The Luding \(M_{S}\) 6.8 earthquake tore the southern part of the 1786 \(M_{S}\) 7.75 rupture zone. However, considering the relatively low fault-locking degree, the strong earthquakes are not urgent in the northern part of the historic rupture zone (Figure 11). Although numerous examples of earthquakes have demonstrated that the low-\(b\)-value area obtained from surface scanning is effective in predicting the location and magnitude of future strong earthquakes [5; 6; 7], our research indicates that neither the fixed-window method nor the non-fixed-window method (HIST-PPM) revealed a significant low-\(b\)-value state in the future epicenter area, resulting in false negatives, whereas \(\Delta\)b could somewhat solve this problem. It seems feasible to use AIC constraints to highlight the \(\Delta\)b-abnormal areas and delineate the location of future strong earthquakes from our example. In addition, using a precise location catalog to calculate the spatial and temporal \(b\)-value profiles can help discover the regions and periods of \(b\)-value anomalies from different perspectives. Figure 10: The rupture regions of \(M\geq 6.5\) historic events along the Xianshui He–Anning He–Zemu He fault belt (modified from [25]), (**a**) AD 1480–1700, (**b**) AD 1701–1800, (**c**) 1801–1900, (**d**) 1901–2022. The gray areas mark the rupture zone of historic events, the two red stars indicate the epicenters of \(M_{S}\) 6.3 Kangding earthquake in 2014 and \(M_{S}\) 6.8 Luding earthquake in 2022. The co-seismic stress transfer produced by large earthquakes has a profound impact on the occurrence of successive earthquakes [80], while the Changes in Coulomb Failure Stress (\(\Delta\)CFS) can describe the transfer pattern quantitatively, which is defined as \(\Delta\)CFS = \(\Delta\tau+\mu\Delta\sigma\), where \(\Delta\tau\) is the change in shear stress, \(\Delta\sigma\) is normal stress change, and \(\mu\) is the coefficient of friction [81].