唐山震区上地壳平均波速比分析

Analysis on average wave velocity ratios of the upper crust beneath the Tangshan seismic zone

收集河北地震台网记录的唐山震区2012-2016年ML≥1.0地震,选取震源深度5-10km、波形信噪比较高的波形数据,拾取直达P波、S波震相到时,利用和达法计算平均波速比,并分析研究区平均波速比水平分布特征与时变特征,结果表明:唐山震区上地壳平均波速比约为1.71,且水平分布呈区域化特征,反映了研究区复杂的地壳结构。研究区内3次ML≥4.0地震前,波速比曲线均呈较显著的下降-低值-回升形态,表明该区平均波速比变化可能具有一定地球物理异常特征。

In this paper, the waveform data of earthquakes recorded by Hebei Seismic Network with ML≥ 1.0 in Tangshan seismic area from 2012 to 2016 is collected, and the records with high SNR and focal depths at 5 to 10 km is selected. Besides, the phases of Pg and Sg are picked, and the velocity ratios of the research region by using multi-station method are calculated. We analyzed the horizontal distribution and time-dependent characteristics of the average wave velocity ratio. It is concluded that the average wave velocity ratio of the upper crust in the Tangshan earthquake zone is about 1.71 with the regionalization of the horizontal distribution of the average wave velocity ratio, reflecting a complex crustal structure. For three earthquakes with ML≥ 4.0, the curves of the average wave velocity ratios all appear changes from low value anomalies to high value anomalies before their events, indicating that the variation of average velocity ratio may have some correlation with the seismic activity in the Tangshan seismic zone.