永登5.8级地震前后波谱参数和Q值变化特征

利用中国数字地震台网（ＣＤＳＮ）兰州台短周期数字地震仪的记录资料，研究了１９９５年甘肃永登ＭＳ５．８地震前后，发生在永登地区小地震的Ｓ波波谱参数，获得以下结果：（１）在永登地震前２年左右，该地区小地震的ＳＣ波波谱拐角频率ｆＣ逐渐下降，由原来的２．４Ｈｚ下降到１．８Ｈｚ．（２）直达波Ｓｇ和地壳内中间层反射波ＳＣ的波谱高频衰减斜率比值γ则先逐渐上升，在临震前１６个月逐渐下降，在下降过程中发生了永登地震，以后又逐渐恢复．（３）用直达横波Ｓｇ的谱参数求出的介质品质因数ＱＳｇ在永登地震前后有较明显的异常变化

VARIATION CHARACTERISTICS OF WAVE SPECTRUM PARAMETERS AND Q VALUE BEFORE AND AFTER THE YONGDENG MS5.8 EARTHQUAKE

Short period digital seismic data of Lanzhou seismic station in Chinese digital seismic network are used to study variation of wave spectrum parameters of small earthquakes in Yongdeng area before and after the Yongdeng M S5.8 earthquake in 1995.The results are the followings: (1) About two years before the Yongdeng earthquake,corner frequence f C of S C wave spectrum of small earthquakes in Yongdeng area fall from 2.4 Hz to 1.8 Hz. (2) Ratio of spectrum attenuation slope in high frequency between S g wave and S C wave increased since 1990,then decreased about 16 months before the Yongdeng earthquake.During the ratio decreasing,the earthquake occurred.After the shock,the ratio value recovered gradually. (3) Anomalies of Q value from spectrum parameters of S g wave appeared before and after the Yongdeng earthquake.