Abstract: Data of earthquakes with magnitude 6.0 occurring between 1962 and 2016 in Sichuan—Yunnan area is used to analyze the relationship between the occurrence of these events with their aftershocks excluded and the variation of velocity of the earth's rotation. The results obtained are as follows: there exists an obvious relationship between the occurrence of earthquakes with magnitude 6.0 occurring in the study area and the extreme point of variation of velocity of the earth rotation. For earthquakes within different magnitude spans, their occurrences are significantly associated with the extreme point of the different periodic variation of velocity of the earth rotation. It have be found that 90% earthquakes with M_S7.0 occurred during a period of time from 14 days before and 37 days after the extreme point of the seasonal variation of velocity of the earth rotation, 80% earthquakes with 6.0 M_S6.4 occurred during a period of time from 68 hours before and 30 hours after the extreme point of the short periodic variation of velocity of the earth rotation, and 87.5% earthquakes with 6.5 M_S6.9 occurred during a period of time from 36 hours before and 64 hours after the extreme point of the short periodic variation of velocity of the earth rotation. By statistical significance test, the above results have passed Z test at 5% level. It shows that earthquakes with magnitude 6.0 in the Sichuan—Yunnan area of China are prone to be caused by the turning changes of velocity of the earth rotation, which could be of some reference significance to predict the occurring time of earthquakes in the Sichuan—Yunnan region of China.

Key words: Sichuan—Yunnan area, Activity of earthquakes, Velocity Variation of the earth rotation, Extreme point