## 4 Discussion  
Based on the analysis of the tectonic stress field and fault slip tendency of the 2021 M\({}_{\text{S}}\) 5.0 Yingjiang earthquake, it is notable that the earthquake was mainly controlled by the tensile stress field and that the inferred strike and dip angles are similar to those of the Xima-Panlongshan fault. The active geothermal fluid activity in this area may have certain implications for the generation mechanism and evolution trend of the mainshock and aftershocks. Relevant studies have proposed that earthquakes caused by the infiltration and diffusion of deep geothermal fluids often show focal migration characteristics, which can be explained by fluid diffusion (e.g., [49; 57; 58]). This study further analyzed the evolution of subsequent aftershock activities. The results are illustrated in Figures 7 and 8. Figure 8 shows the distribution of all of the aftershocks in the three-dimensional direction over time (12 June 2021-3 December 2021). Notably, the aftershock sequence has an outward migration trend overall. Figure 7a shows the aftershock evolution into two distinct spatial subsequences, which are circled with gray and blue ellipses and labeled as aftershock sequences S1 and S2. Subsequence S1 includes the aftershock events occurring between the main earthquake and 3 September 2021, represented by small gray circles. Subsequence S2 includes the aftershock events occurring between 4 September 2021, and 31 December 2021, represented by small blue circles. S1 takes the M\({}_{\text{S}}\) 5.0 main shock as the starting point, and S2 takes the M\({}_{\text{S}}\) 3.2 aftershock (24.99\({}^{\circ}\) N, 97.85\({}^{\circ}\) E) on 4 September 2021, as the starting point. There are obvious differences between S1 and S2 in terms of the spatial distribution of aftershock activity. Subsequence S1 closely surrounds the epicenter of the M\({}_{\text{S}}\) 5.0 mainshock, while subsequence S2 is relatively closer to the Tenglagong hot spring (25\({}^{\circ}\) N, 97.77\({}^{\circ}\) E). Figure 7: **(a)** Spatial distribution of the aftershock sequence following the 2021 M\({}_{\text{S}}\) 5.0 Yingjiang earthquake. According to the occurrence time, the aftershock sequence is divided into two subsequences: gray (12 June 2021–3 September 2021) and blue (4 September 2021–31 December 2021). The red rectangle in the figure indicates the main distribution area of the aftershocks. The red star is the mainshock, and the small red solid square indicates the location of the Tenglagong hot spring. **(b,c)** Sections along the depth of the aftershock sequence. We utilized the method described by [PERSON] et al. [49] to further analyze the diffusion properties of subsequences S1 and S2. Figure 9 shows the diffusion analysis results of the sequence. Figure 9a shows the distribution of the magnitudes of events during the entire earthquake sequence over time. The M\({}_{5}\) 3.2 aftershock on 4 September 2021 was the first large aftershock after the main earthquake. [PERSON] et al. [49] proposed that the distribution of the aftershock sequence corresponds to the displacement curve of pore pressure diffusion if the appropriate hydraulic diffusivity D is selected. Figure 9b,c depicts the diffusion distributions of the two subsequences with different hydraulic diffusivities. Figure 9b demonstrates that subsequence S1 has good consistency with the diffusion front curve of D = 4.50 m\({}^{2}\)/s, while Figure 9c shows that subsequence S2 corresponds well to the diffusion curve of D = 2.80 m\({}^{2}\)/s. These results indicate that the distributions of the two aftershock sequences were affected by the diffusion and migration of geothermal fluids to a certain extent, but the correlation of subsequence S2 is more conspicuous. In addition, the two subsequences include some aftershocks close to D = 10.20 m\({}^{2}\)/s and D = 5.00 m\({}^{2}\)/s, which suggests the presence of some faults with high diffusivity in the Yingjiang area, which is consistent with previous studies [49].