Abstract: Based on the digital waveform data recorded by the Yunnan Digital Seismic Network in 2008, the source parameters of the 2008 Yingjiang earthquake sequence are obtained by applying spectrum analysis and the Brune’s source model. The correlation coefficients are calculated using the low-frequency spectral amplitude recorded by the same station for 2 events, and the events with similar focal mechanism can be grouped using clustering method. Comparing with the obtained focal mechanisms, it is found that there are good relations in the trend of P axes in each group and if there are higher correlation coefficients, the trend of P axes are closer. The Yingjiang area is divided into 3 studied regions to analyze the stress levels and stress directions by combining the source parameters and the mean focal mechanism of each group. The results show that the change and transformation of types of focal mechanism solutions at different stages reflects the temporal characteristics of the regional stress field, and that a type of earthquake focal mechanism solutions concentrated in a time period and switching to regional stress field may be a sign of strong earthquakes. There is some relationship between the stress drop and the type of focal mechanism. The closer the direction of the focal mechanism in a group close to the region stress field, the higher the stress drops increase.

Key words: Stress drop, Correlation of focal mechanism, Clustering group, Stress field, The 2008 Yingjiang earthquake sequence