## 4 Accurate Earthquake Locating
The black dots in the maps are the relocated \(M_{L}\geq 1.5\) quakes from 2009 to May 2022. The yellow star shows the epicenter of the \(M_{S}\) 6.8 Luding earthquake on 5 September 2022. F1: Xianshui He fault belt, F2: Anning He fault belt, F3: Zemu He fault belt, F4: Daliang Shan fault belt. The red arrows indicate the movement directions of the blocks. May 2022. Additionally, the \(b\)-value in the latter period significantly decreased compared to the former. The anomaly area was set at the intersection and bending parts of faults, where significant strains can accumulate [68; 69]. The future Luding \(M_{S}\) 6.8 earthquake (yellow star in Figure 6) is located in this anomaly area (Figure 6b). Considering that some earthquake cases indicate an increase in seismic activity before strong earthquakes [70; 71; 72; 73] or some special spatiotemporal migration patterns [74; 75], we analyzed the spatiotemporal distribution characteristics of earthquakes of \(M_{L}\geq 3.0\) within a 100 km range, with the Luding \(M_{S}\) 6.8 earthquake as the center (Figure 6c). We noticed that, since 2015, the seismicity rate of earthquakes of \(M_{L}\geq 3.0\) within a range of 50 km has been higher than that of the background period, which is also the spatiotemporal domain where the \(b\)-value exhibits anomalies. Although we did not observe any obvious migration pattern before the mainshock, a small magnitude swarm near the future mainshock occurred from December 2021 to March 2022 (red rectangle in Figure 6c). More detailed research is needed to determine the relationship between these small earthquakes and the major earthquakes that will occur in the recent future that will occur six months later. The \(\Delta\)AIC value of the adjacent southern segment of the Longmen Shan fault belt is as high as 15, indicating that seismic activity changes intensely there. However, the \(\Delta b\)-value in this area is positive. The Qiaojia (QJ) area in the southern part of the study area also has a high \(\Delta\)AIC value, which may be due to weak monitoring capabilities at the boundary of the station network (Figure 6a). Along the strike of the Xianshui He fault belt, we have drawn a seismic profile from Daofu (DF) to the south of Shimian (SM) (see Figure 3b for the location of the profile). The projected width of the profile is 30 km on each side, and the \(b\)-value is calculated using a rectangular statistical window with a horizontal width of 10 km and a vertical width of 3 km. The sliding increment in both directions is 1 km. At the same time, it is required that there be at least 30 samples with \(M_{L}\geq 2\) in the statistical window. Figure 6: (**a**) Map of \(\Delta\)AIC—only the \(\Delta\)AIC \(\geq\) 2 areas are plotted; (**b**) map of \(\Delta\)b—only the corresponding areas with \(\Delta\)AIC \(\geq\) 2 are plotted. The yellow star shows the epicenter of the \(M_{S}\) 6.8 Luding earthquake on 5 September 2022. The solid circle indicates a 100 km-radius study region of the space-time diagram, which is portrayed in figure (**c**). The dashed box is corresponding to the 50 km-radius abnormal region of the \(b\)-value from 2015 to 2022. The red rectangle indicates the position of the nearest cluster of \(M_{L}\geq 2\) to the Luding \(M_{S}\) 6.8 earthquake. F1: Xianshui He fault belt, F2: Anning He fault belt, F3: Zemu He fault belt, F4: Daliang Shan fault belt. The focal profile from 2009 to 2014 shows (Figure 7a) that the clustering characteristic is significant. The earthquakes from Daofu (DF) to Shimian (SM) are mainly distributed within a depth of 10 km (cluster1, C1), while the number of earthquakes within a depth of 8 km to the Shimian (SM) area is scarce, and the earthquakes are clustered between 8 and 14 km in depth (cluster2, C2). Another cluster is located south of Shimian (SM), which is clustered in the depth range of 17-30 km (cluster 3, C3).