## 3 Results
### Analysis of Fault Slip Tendency in the Yingjiang Area  
Based on the stress inversion results, the slip tendency of faults in the Yingjiang area was further analyzed (Figures 5 and 6). Figure 5 shows the Mohr circle under the normalized normal-shear stress coordinates, and the frictional coefficient is prescribed as 0.6 [56]. To analyze the relationship between different fault kinematics and slip tendency and the relationships among faults and strike, dip, and rake angles, we discussed these aspects separately according to the classification method in Section 2.1. Figure 6 further describes the distribution characteristics of the slip angle and normalized slip tendency in the strike-dip coordinate system and the distribution of historical earthquakes in the Yingjiang area. As shown in Figure 6, the faults with a considerable slip tendency strike -40\({}^{\circ}\) to -80\({}^{\circ}\) or -110\({}^{\circ}\) to -150\({}^{\circ}\) and dip -60\({}^{\circ}\) to -90\({}^{\circ}\). In Figure 6a, there are only two historical compressive earthquakes, and it can be seen that the slip tendencies of the two earthquakes are low. Figure 6c includes the distribution of strike-slip earthquakes, and it is notable that these strike-slip earthquakes have high slip tendencies. Figure 6e shows the distribution of 7 historical normal fault earthquakes, two of which have relatively high slip tendencies. Figure 6g describes oblique earthquakes, most of which have high slip tendencies according to the distribution of focal spheres. In summary, most of the seismogenic faults of historical earthquakes in the Yingjiang area have a high slip tendency; that is, they have a high degree of instability. Among them, strike-slip faults and oblique faults are more prone to slip, and NE-trending faults have a relatively higher slip tendency. Figure 5: Mohr circle under normalized normal stress–shear stress coordinates. The colored spheres indicate the focal mechanism of selected earthquakes from this study. The blue line is the failure criterion when hydrostatic pressure is considered, and the black line is the failure criterion when the pore pressure is zero. Figure 6 shows the characteristics of faults with a considerable slip tendency, which indicates that the faults may rupture and cause earthquakes in the future. The Xima-Panlongshan fault, which is close to the epicenter of the 2021 Yingjiang earthquake, has a strike of approximately N45\({}^{\circ}\)E and a dip angle of 85\({}^{\circ}\)[2], which coincides with our estimation. However, the nearby Sudian fault, whose strike is close to N-S and whose dip angle range is 65\({}^{\circ}\) - 85\({}^{\circ}\), is not within this range. According to the focal mechanism solution of the M\({}_{5}\) 5.0 Yingjiang earthquake determined by [PERSON] et al. [7], nodal plane I has a strike of N31\({}^{\circ}\)W and a dip angle of 90\({}^{\circ}\), and plane II has a strike of N59\({}^{\circ}\)E and a dip angle of 85\({}^{\circ}\). The focal fault indicated by nodal plane II has a near-NE-SW strike and an approximately vertical dip angle, which is similar to the characteristics of the Xima-Panlongshan fault, which has a considerable slip tendency. In addition, a total of 116 relocated aftershock events following the 2021 Yingjiang mainshock until December 31, 2021, were selected for performing temporal and spatial characteristic analyses. Figure 7a displays the spatial distribution of aftershocks, and two sections (AA' and BB') were selected along and perpendicular to the direction of the aftershock distribution. The BB' profile line is also approximately parallel to the strike of the Xima-Panlongshan fault. The sections along the depth are shown in Figure 7b,c, and the color change of the circles shows the distribution of aftershocks over time. Figure 7b shows that the aftershock migrates northwestward (near A) with time. Figure 7c shows that the aftershock also migrates along a direction approximately parallel to the Xima-Panlongshan fault (near B).