RESEARCH ON THE REGIONAL Q VALUES OF CODA WAVES FOR THE AFTERSHOCKS IN LUQUAN, YUNNAN OF 1985

On the basis of a scattering model to explain the coda waves of local and regional earthquakes (K. Aki, 1969), data are obtained from over 68 aftershocks with magnitudes between 3.0 to 4.9 of the Luquan earthquake, recorded by 12 VGK short-period seismogrphs of the Seiemic Network of Yunnan Province. For six time windows are determined the coda Q values, the data cover a range of frequencies from 0.40 to 1.65 Hz. The frequency dependence of Q is observed in the range of frequencies considered. The estimated coda Q values is 80 to 240, the coefficient of frequency dependence is = 0.45. The source factor Bfp = 10-23-10-24, a measure if the intensity if scattering is obtained for 10 stations. The regions of lower Q values exhibit strong scattering. It should be noted that the aftershock coda Q is about a half of the normal value for near stations before the Luquan earthquake. This variation of Q may be taken as a significance earthquake precursor in predication of seismic trend.In addition, the aftershock source parameters are determined, and the quantitative relationships among the source parameters are discussed. For 3.0MLL + 11.335, E = (2.1010-5) Mo, a =0.40-0.80km, = (6.0-130) 105 Pa. A significant result is that there is no linear relationship between and ML.