## 4 Discussion
Figure 8: Time distribution of aftershock sequence in the 3D direction. X follows the longitude direction, Y follows the latitude direction, and Z follows the depth. The gray circle represents the earthquake sequence, and the large gray circle is the main earthquake. Considering that the Yingjiang area is located in the western Tengchong volcanic area, hot springs are widely distributed, and geothermal activity is strong. The Tenglagong hot spring (25\({}^{\circ}\) N, 97.77\({}^{\circ}\) E) is closest to the epicenter of this earthquake. Spring water has a temperature of 62 \({}^{\circ}\)C and a flow rate of 1.5 L/s [16]. Moreover, the M\({}_{5}\) 5.0 Yingjiang earthquake was located at the intersection of two strike-slip faults (Figure 1). Under the extensional action of the two groups of faults, the intersection area has a low strength and is conducive to fluid activity. [PERSON] and [PERSON] [59] asserted that underground fluids are more likely to flow along the tensional area of strike-slip faults. In addition, the 2011 M\({}_{5}\) 5.8 Yingjiang earthquake (24.7\({}^{\circ}\) N, 97.9\({}^{\circ}\) E) occurred in the same area as the epicenter of the 2021 M\({}_{5}\) 5.0 Yingjiang earthquake. The tomographic imaging results found that the epicenter of the 2011 Yingjiang earthquake was located adjacent to a low-velocity anomaly caused by the upwelling of an active volcano (e.g., [20]). Abundant geophysical evidence suggests that the Yingjiang earthquake may have been a fluid-driven earthquake associated with volcanism (e.g., [20]). Furthermore, previous studies (e.g., [60; 61]) have proposed that there are several key factors affecting fault activation, including fault geometry (orientation, size, and surface features), stress field characteristics, and frictional properties (friction coefficient and cohesion). When a fault is in the state of imminent slip, a small stress change driven by geothermal fluid may enhance fault instability, thus controlling the occurrence of earthquakes. There are anomalous low-velocity areas near the focal points of some earthquakes, and these anomalies are considered as evidence of the presence of fluids. These fluid-filled areas have high pore pressures, which reduces the effective stress of faults and encourages fault slip and destabilization, resulting in earthquakes (e.g., [62; 63; 20; 64]). It is worth noting that previous studies [55; 65] have noted a low-velocity anomaly region located in the epicenter zone of the Yingjiang earthquake sequence, and this low-velocity region is proposed to reflect magma activity in a molten or semi-molten state. In addition, the water radon at Longling station (approximately 86 km away from the Yingjiang M\({}_{5}\) 5.0 earthquake, east of the epicenter) has been detected with an abnormally low value since late February 2021, and the temperature of water has also been detected with a high value anomaly since early August 2020 [e.g., 66]. After the Yingjiang earthquake, these anomalies gradually  
Figure 9: Distribution of aftershock sequences. The large gray circle represents the M\({}_{5}\) 5.0 mainshock, and the small gray and blue circles represent the aftershocks. The gray and blue curves are the corresponding diffusion fronts under the calibrated hydraulic diffusivity (D). (**a**) The distribution of aftershock magnitude with time. (**b,c**) The distribution of the relative distance of the aftershock sequence with time. changed into normal conditions. A previous study suggested that these fluid anomalies might be related to this 2021 M\({}_{\text{S}}\) 5.0 Yingjiang earthquake occurrence [66]. Although the seismogenic mechanism of the 2021 M\({}_{\text{S}}\) 5.0 Yingjiang earthquake was dominated by the tectonic stress field, considering its seismogenic mechanism and the conspicuous migration of the aftershock sequence, we recognize that the diffusion and migration of geothermal fluids influenced the development of subsequent seismic activity.