山西地区Pb震相识别及特征研究

Study on identification and characteristics of the Pb phase in shanxi area

针对山西地区Pb震相难以准确识别的现状,本文首先根据地壳速度模型计算了能够记录到Pb震相的震中距范围.然后针对Pb作为初至、后续震相分别提出了相应的识别方法:当Pb作为初至震相时周期大于Pg,振幅小于Pg,波性特征与Pn相似,可使用理论到时与波形特征相结合的方法识别;当Pb作为后续震相时,振幅和周期都不稳定、存在突变点,综合使用理论到时、波形特征和离散小波变换三种方法进行识别.最后,依照上述方法识别、标定了56个地震事件中的236个Pb震相,计算得出山西地区下地壳P波的速度为6.73 km/s,康拉德面的埋藏深度为21 km.

The Pb phase of Shanxi area is difficult to be identified accurately in the present. Based on the crustal velocity model,we firstly calculate the range of the epicenter distance which can record the Pb phase in this paper. For Pb as initial and later seismic phase,we put forward the corresponding identification methods,respectively. When the Pb is as the initial seismic phase,the period is longer than the Pg and the amplitude is less than Pg. The characteristic of Pb waveform is similar to Pn,then we can use the combined method of the theoretical arrival time and waveform characteristics to identify the Pb. When Pb is as the later seismic phase, the amplitude and period are unstable and has some breaking points,using the three methods of theoretical arrival time,waveform characteristic and discrete wavelet transform for identification. Finally, according to the above methods, we identified 236 Pb phase in 56 seismic events,and calculated that the velocity of P wave in the lower crust of Shanxi area is 6. 73 km/s and the depth of Conrad’s discontinuity is 21 km.