中强地震前中小地震速度谱的变化特征

从Ｄｕｄａ和Ｎｏｒｔｍａｎｎ提出的谱震级定义出发，利用江苏地区遥测台网的５个台站记录到的５４次地震的数字化垂向位移波形记录，采用１３组０．５倍频程的滤波器，计算了各次地震的Ｐ波和及Ｓ波在没中心周期处的平均速度谱值，研究了地震的Ｐ波或Ｓ波速度谱的拐角周期及综合因子ｆ值的时间变化特征。结果显示：中强地震发生之前１年或更短的时间内所发生的中小地震，其速度谱综合因子ｆ值随时间的变化具有由高值向低值的变化趋

A STUDY ON CHANGE OF VELOCITY SPECTRUM OF MEDIUM-MINOR EARTHQUAKES BEFORE MEDIUM-STRONG EARTHQUAKES

According to the definition for the spectral magnitude advanced by Duda and Nortmann,using the digital vertical displacement data recorded by 5 telecontrol stations in Jiangsu area and 13 groups of 0.5-octave band-pass filters of which central period are 1.2 s,1.0 s,0.67 s,0.4 s,0.25 s,0.147 s,0.119 s,0.1 s,0.078 s,0.065 s,0.054 s,0.047 s,0.041s respectively,the average velocity spectra of P and S wave of 54 earthquakes has been determined.And the synthetical fact f of each earthquake can be gotten.Change feature of corner periods of the velocity spectra of P and S wave and the f values with time are studied.The results show that the synthetical fact f of velocity spectrum of medium-minor earthquakes changed from high to low with time during one year or shorter period before medium-strong earthquakes which occurred in the duration of low f-value.