2012年印尼8.6级地震应变地震波的Hilbert-Huang时频分析

本文通过端点效应压制的Hilbert-Huang变换, 对大同及沁源台布置的四分量钻孔应变仪记录的印尼8.6级地震激发的应变地震波形进行时频分析, 结果显示印尼8.6级地震的主震和8.2级余震的应变地震波序列各个震相具有不同的时频特征: ① 地震波到达之前的所谓“环境噪声”部分, 瞬时频率低, 瞬时振幅小; ② P波初至时, 高频成分突然增加, 振幅也随即增强; ③ S波到达时, 频率有所降低而振幅剧烈上升; ④ 面波到达时, 振幅进一步剧烈上升达到整个序列的极大值; ⑤ 尾波部分振幅逐渐降低, 但与噪声部分相比频率依然偏高, 振幅依然偏大。 本文也将应变地震波与地震仪记录的地震波进行对比, 虽然应变地震波与地震波波形和Fourier谱具有极高的相关系数, 但从Hilbert-Huang变换得到的边际谱上看, 应变地震波与地震波有显著的区别, 应变地震波比地震波记录的低频成分相对更多。 通过Hilbert谱, 有助于更好地了解非平稳信号的局部特征, 对于突变信号的地震波, Hilbert-Huang变换是一个较好的时频分析工具。

Time-frequency Analysis of the 2012 Indonesia M8.6 Earthquake Strain Seismic Waves by Means of Hilbert-Huang Transform

We use the endpoint suppression Hilbert-Huang transform to analyse the Indonesia M8.6 earthquake strain seismic waves recorded by four-component borehole strain meters located at Datong and Qingyuan in time and frequency domain. The result shows that different phases of the strain seismic wave of both the M8.6 main event and M8.2 aftershock eventshows different significant time-frequency features.Before the waveforms arrive, instantaneous frequency is low and instantaneous amplitude is small. At P wave first arrival, high frequency components appear of a sudden increase, at S wave arrival, lower frequency and amplitude rise sharply. When surface wave arrives, the amplitude further rises and reachesthe greatest value of the entire sequence. Coda amplitude decreases gradually, but the frequency is still high compared to the noise portion. The amplitude is still much larger. Although strain seismic wave and seismic wave have a correlation coefficient of up to 0.93, through the Hilbert-Huang transformation, the marginal spectrum shows that strain seismic wave andseismic wave are remarkably different. Strain seismic records have relatively more low frequency component. Hilbert spectrum is helpful in understanding the detailed characterof non-stationary signal. For transient signals of strain seismic wave, Hilbert-Huang transform is an effective time-frequency analysis tool.