永登5.8级地震前后小震的震源参数和介质Q值变化特征研究

The variation of characteristics of source parameters and medium Q values for small shocks before and after Yongdeng M S5 8 earthquake

利用中国数字地震台网（ＣＤＳＮ）兰州台记录的短周期垂直向直达Ｐ波数字地震资料，通过频谱分析的方法，测定了１９９５年７月２２日永登ＭＳ＝５．８地震前后发生在该区的３３个小震的震源参数（地震矩，应力降和震源尺度）及介质品质因子Ｑ值。研究区域内介质品质因子Ｑ＝５５～１０９，前震平均值为９３，余震平均值为７４；应力降Δσ＝（１．３２～４１．４１）×１０５Ｐａ，前震平均值为３．３１×１０５Ｐａ，余震平均值为１３．６４×１０５Ｐａ；地震矩Ｍ０＝（０．２６～７．４９）×１０１５Ｎｍ；震源尺度ａ＝０．６７～１．１４ｋｍ。

In this paper,by using spectral analysis method for the short period digital data of vertical component direct P wave recorded at CDSN Lanzhou seismic station.We have determinated the source parameters(seismic moments,stress drops and source dimensions)and the medium Q values of 33 small shocks before and after Yongdeng M S5 8 earthquake.The results show that in Yongdeng region,the medium Q values range from 55 to 109,the average Q of foreshocks is 93,and the average Q of aftershocks is 74;the stress drops range from 1 32×10 5 Pa to 41 41×10 5 Pa,the average Δ σ value of foreshocks is 3 31×10 5 Pa,and the average Δ σ value of aftershocks is 13 64×10 5 Pa,the seismic moments range from 0 26×10 15 N·m to 7649×10 15 N·m.and the sourcc,dimensions from 0 67 km to 1 14 km.