We have studied the data from the digital earthquake net of Yunnan province using the earthquake doublet theory proposed by French seismologist G.Poupinet and his co-workers.Eight groups of multiplet and seven groups of doublet of Wuding earthquake have been obtained from observations at Yimen station by baseline correction

digital filter and waveform contrast

etc.The Fourier transformations of these doublets are calculated individually with respect to the initial 3s from the P-wave arrival and the slope of decimal logarithms of spectral ratios versus frequency is estimated.The results show that absolute values of P-wave spectral ratio slop are all more than 0.030 for the earthquake doublets with one event occurring 7 months before the Yao′an M

L

6.5 earthquake and the other occurring outside that period

significantly higher then the earthquake doublets precedi

ng the Yao′an earthquake by more than 7 months.The variation in spectral ratio slop is observed in a sector of azimuth around 2° of the main shock.The doublets observed on Changshu Station following the South Yellow Sea middle-intense earthquakes show such variations in spectral ratio slope

but the time scale of one event of the doublets extends to 9 months before the main shock.