Using the data from more than 100 meteorological stations, this paper preliminarily analyzes the effect on earthquake occurrences by the variations of atmospheric pressure field during the last two years or longer in the southwestern areas of China, yielding results show that when the 24-hour atm. variation in Yunnan area and its neighborhood (mostly in the Sichuan basin) appears a high value and then reaches a certain index) i. e. △P_ij=P_ij-P_i-1,j(i:date, j:month) we have:
△P_ij ≥ 1.4σ_j (j=Jan., Feb., …Dec.; σ_j=standard deviation). If a relatively low atm. pressure is also detected in the same period in Yunnan area, there might be possibility for occurrences of M_L ≥ 4.0 events in Yunnan region and its neighborhood. The 91.8% prediction accuracy can be maintained for earthquake occurrences within the following 7 days, and 84,5% prediction accuracy can also be reached for earthquake occurrences in the following 5 days. The epicentres of the earthquakes nearly all distribute appears the areas where the greatest strength of low atm. pressure, or it is on the shearing belt of the high-and low-atm. pressures.
Finally, the paper briefly discusses the possible connections between the above-mentioned two situations.