###### Abstract  
On 12 June 2021, an earthquake with M\({}_{\rm S}\) 5.0 occurred in Yingjiang, adjacent to eastern Myanmar, where seismic activity is frequent due to plate collision. To explore the mechanism of this earthquake, the regional stress field of the Yingjiang zone was inverted using the focal mechanisms of 187 historical earthquakes in this area. Furthermore, based on the obtained orientation of the principal stress axes and the stress shape ratio, the fault slip tendency (Ts) was also estimated to evaluate fault instability in the study area. The stress variation results show that the diffusion and migration of the aftershocks suggested strike-slip-type stress accumulation in Yingjiang with a principal compressive stress axis direction-oriented NNE-SSW. Fault slip tendency results show that the seismogenic faults feature strikes within the ranges of 40-80\({}^{\circ}\) and 110-150\({}^{\circ}\) and dips of 60-90\({}^{\circ}\) and exhibit enhanced stress coupling. The distribution of the aftershock sequence is conjectured to have a high correlation with local fluid migration and was likely controlled by the hydrated rock-induced ruptures of the stressed fault systems near the source region. This study provides insights into potential earthquake risks in this region. Y 2023 13 957 11  
The Nabang fault, adjacent to the western margin of the Tengchong block (Figure 1), is an important component of eastern Myanmar's Mogok metamorphic belt [8; 9; 10]. Since the Cenozoic, both the Nabang strike-slip fault and the Gaoligong strike-slip fault (Figure 1, Gaoligong F.) have recorded a strong right-lateral strike-slip motion, and they were once the western boundary of the extruded Indo-Chinese block (e.g., [8; 9; 10]). The Sudan fault extends northward to Myanmar and southward to Yingjiang with a total length of nearly 100 km. The overall fault strikes \(\sim\)N-S. The fault has been dominated by dextral strike-slip kinematics since the late Quaternary [11]. The southern tip of the fault was subjected to intense extension, and it coated with the Dayingjiang fault to form a triangular fault depression area (e.g., [4]). The Xima-Panlongshan fault is approximately 30 km long, NE-SW-striking, and dips 85\({}^{\circ}\) toward SE. It is an early-middle Pleistocene fault [2] and can be considered an extension of the Sudian fault [2]. Figure 1: (**a**) Seismotectonic map of the Yingjiang area describing the tectonic setting and seismic activity distribution. Black lines are the main faults, and red lines are secondary faults (e.g., [11; 12; 13; 14]). Yellow circles indicate the distribution of historical earthquakes in Yingjiang (data obtained from NEDC, [[https://data.earthquake.cn](https://data.earthquake.cn)]([https://data.earthquake.cn](https://data.earthquake.cn)), accessed on 15 December 2022). Blue arrows represent the GPS velocity vectors [15]. Red squares indicate the distribution of 24 hot springs in the study area [16; 17]. The thick white dashed line illustrates the tectonic boundary of the Tengchong block [18]. Inset is the location map. Black arrows in the inset show GPS velocity vectors of crustal motion relative to Eurasia [19]. (**b**) Distribution of focal depths of historical earthquakes in Yingjiang. Previous studies have analyzed the tectonics and seismic activity in the Yingjiang area and obtained meaningful outcomes. [PERSON] et al. [20] presented the results of three-dimensional tomography in Yingjiang, revealing a low-velocity anomaly near the epicenter of the 2011 Yingjiang earthquake, and deduced that the earthquake might be volcano-related and fluid-driven. According to [PERSON] et al. [21], the 2011 M\({}_{\rm S}\) 5.8 Yingjiang earthquake was caused by the horizontal movement of the Baoshan-Tengchong block under the dual effect of the northeastward compression between the Indian plate and the Eurasian plate and the northeastward subduction of the Myanmar arc, which led to left-lateral a strike-slip motion in the Dayingjiang fault zone. [PERSON] et al.