Time-frequency analysis of Jiuzhaigou M7.0 seismic acceleration record based on Hilbert-Huang transform
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摘要: 2017年8月8日四川九寨沟M7.0地震是继2008年汶川M8.0地震和2013年芦山M7.0地震之后，青藏高原东缘在不到10年的时间内发生的第3个震级M7.0以上的强震，震中位于青藏高原巴颜喀拉块体东缘东昆仑断裂带东端的塔藏断裂、岷江断裂和虎牙断裂交汇部位，四川省地震局的数字强震台网共有37个台站获取了主震的三分量强震加速度记录。由于傅里叶（Fourier）变换仅能提供强震记录的频域信息，故本文在对九寨沟M7.0地震的加速度记录进行时频分析时采用了一种基于聚类经验模态分解（EEMD）的希尔伯特-黄变换（HHT）方法提取信号时频特性，通过对震中附近台站的加速度记录进行EEMD分解和希尔伯特（Hilbert）变换及谱分析，最终有效获得了信号能量的时频分布特征，量化提取了中心频率、Hilbert能量、最大振幅对应的时间等特性，并与Fourier变换进行了对比研究。研究结果表明：对于非线性的强震记录采用EEMD能够有效抑制经验模态分解（EMD）中存在的模态混叠问题，FFT谱与Hilbert边际谱相比，它在低频处会低估地震动的幅值，随着频率的增加，FFT谱又会放大其幅值。Abstract: On 8 August 2017, the Jiuzhaigou M7.0 earthquake following the Wenchuan M8.0 earthquake and the Lunshan M7.0 earthquake was the third strong shock in the past 10 years in the eastern margin of the Qinghai-Tibetan Plateau. The Jiuzhaigou earthquake occurred in the intersection area among the Tazang, Minjiang and Huya faults in the eastern part of the Bayan Har block of the Qinghai-Tibet Plateau. In this paper, Time-frequency characteristics of the method is used based on EEMD decomposition extraction signal in the treatment of the Jiuzhaigou M7.0 earthquake records. Through EEMD decomposition, Hilbert transform, and spectral analysis on the acceleration records of stations near the epicenter, the time-frequency distribution characteristics of the signal are effectively obtained. The characteristics of the center frequency, Hilbert energy, and maximum amplitude are extracted quantitatively. And a comparative study between the Fourier transform and wavelet transform was made. The study shows that for the non-linear strong earthquake records, EEMD can be used to inhibit the existing problem of mode mixing of EMD decomposition. In low frequency, the amplitude of ground motion is underestimated. With the increase of frequency, FFT spectrum will magnify the amplitude.
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Key words:
- EEMD /
- HHT /
- acceleration records /
- time-frequency characteristics /
- Hilbert spectrum
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图 6 HHT瞬时能量谱
（a）九寨白河台EW向； （b）九寨白河台SN向； （c）九寨白河台UD向； （d）九寨勿角台EW向； （e）九寨勿角台SN向； （f）九寨勿角台UD向
表 1 IMF分量统计特征值
模态分量 平均周期/s 最大振幅/cm•s–2 中心频率/Hz 最大振幅对应
的时间/sIMF1（C1） 0.208 5 61.769 1 4.309 3 27.655 0 IMF2（C2） 0.099 2 23.501 6 9.595 3 27.690 0 IMF3（C3） 0.128 2 41.770 8 8.106 0 28.670 0 IMF4（C4） 0.220 8 29.159 4 4.297 1 34.160 0 IMF5（C5） 0.335 0 17.057 3 2.704 0 31.575 0 IMF6（C6） 0.555 1 4.223 70 1.880 0 23.805 0 IMF7（C7） 1.201 1 3.444 50 1.196 4 32.105 0 IMF8（C8） 2.558 2 3.950 60 0.439 5 29.795 0 
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