安庆4.8级地震余震的波速比和波谱异常分析

Anomaly Analysis on Vp/Vs Ratio and Spectrum of the Aftershocks of the Anqing Earthquake of M4.8

利用安徽数字地震台网安庆台记录的地震波形资料,采用单台法,计算2011年1月19日安徽安庆4.8级地震余震的波速比及利用Matlap程序计算其卓越频率,得出以下分析结果:1)波速比存在高低值异常分布,低值地震沿断裂带分布,对应地震的高频度、高强度阶段,表明该地震序列是在波速比低值异常状态下发生;处于序列后半段的余震,波速比则呈现整体高值状态,并沿区域应力场主压应力方向分布,可能是受到震源区应力调整的影响。而整个序列波速比的平均值为1.740与该区域背景值1.730基本一致,可能反映了该区域基本处于较稳定状态,发生较大地震的可能性不大。2)主震后,波速比开始上升,几次较大余震前,均呈下降的趋势,震后开始回升。3)主震后,纵横波卓越频率比迅速下降,几次较大余震前均呈现异常低值(<1.0)的状态,之后上升的过程中发生较大余震。这些结果可为较大余震的预测提供参考。

Based on earthquake wave data recorded by Anqiug station of the Anhui Digital-Seismic Network, Vp/Vs ratio of the aftershocks of the 19 January, 2011 Anqing earthquake, Anhui, of M4. 8 , by using single station method, and their predominant frequency, by using Mathlab program, are calculated. The result is that： 1 ） There exists anomaly distribution of high and low value in Vp/Vs ratio. The earthquakes distribute along fault belt where low value appears, corresponding to the high seismic frequency and strength, which indicates that earthquake sequence occurs at the state of low value anomaly of Vp/Vs ratio, whereas for the aftershock sequence during post stage, Vp/ Vs ratio appears in whole high value and distributes along with principal compression stress axis of the regional stress field, which may be relevant to stress adjustment in the source area. The average of Vp/Vs ratio of the entire sequence is 1. 740, near to the background value 1. 730, which may shows that the region is basically in a steady state where a larger earthquake occurs with little possibility. 2 ） The Vp/Vs ratio begins to rise after the mainshock, whereas Vp/Vs ratios go down before some large aftershocks and then rise after quakes. 3 ） After the mainshock,the ratio of predominant frequencies of P and S wave reduce immediately. The abnormal low values（ 〈 1.0） appear before some large aftershocks, and then some larger aftershocks occurs during rising process. These results may be taken as references for the prediction of larger afterearthquakes.