2022年泸定M_(S)6.8地震前超低频事件的检测分析  

Detection and analysis of very low frequency earthquakes before the 2022 Luding M_(S)6.8 earthquake

作　　者：张晓阳 邓津[1,2,3] 李淑婷 ZHANG Xiaoyang;DENG Jin;LI Shuting(Lanzhou Institute of Seismology,CEA,Lanzhou 730000,Gansu,China;Gansu Lanzhou Geophysics National Observation and Research Station,Lanzhou 730000,Gansu,China;Key Laboratory of Loess Earthquake Engineering,CEA,Lanzhou 730000,Gansu,China)

机构地区：[1]中国地震局兰州地震研究所,甘肃兰州730000 [2]甘肃兰州地球物理国家野外科学观测研究站,甘肃兰州730000 [3]中国地震局黄土地震工程重点实验室,甘肃兰州730000

出　　处：《地震工程学报》2025年第3期727-740,共14页China Earthquake Engineering Journal

基　　金：甘肃省地震局地震科技发展基金(2020GZ02);中国地震局兰州地球物理国家野外观测站项目(2021Y02);甘肃省青年科技基金(22JR11RA089);甘肃省青年科技基金(22JR5RA827)。

摘　　要：2022年9月5日,四川省甘孜州泸定县发生M_(S)6.8地震。泸定地震前震源区发生的以超低频地震形式出现的慢地震,对理解主震的震源物理过程有重要意义。通过希尔伯特变换和短时傅里叶变换对泸定地震主震前发生的超低频地震进行检测,初步分析其记录台站、频谱特征和时间序列特征。结果显示:主震前共检测到14次超低频地震,在垂直和水平分量均能有效检测到,且垂直分量的检测效果更为显著;振幅较大、持续时间较长的超低频地震在希尔伯特变换检测中识别效果佳,而振幅较小、持续时间较短以及事件波形有重叠的超低频地震在短时傅里叶变换检测中可以有效识别;有67.7%的台站成功记录了所有超低频事件,表明观测结果具有较强的可靠性。超低频地震在相对较低的频率范围内有明显的谱峰,峰值频率主要集中在0.06~0.16 Hz,与天然地震的频率范围有明显差别。主震前18 h发生了振幅最大的超低频地震,之后频次呈增加趋势,且伴随小地震的增多。这可能反映了地壳中应力通过超低频地震和小地震的方式逐步释放,直到主震发生。On September 5,2022,an M_(S)6.8 earthquake struck Luding County,Ganzi Prefecture,Sichuan Province.Slow earthquakes manifested as very low frequency earthquakes occurring in the source region before the Luding earthquake hold significant implications for understanding the source physical processes of the mainshock.This study employs the Hilbert transform and short-time Fourier transform(STFT)to detect very low frequency earthquakes preceding the mainshock,with preliminary analyses of their recording stations,spectral characteristics,and temporal features.The results indicate the following:(1)A total of 14 very low frequency earthquakes were detected before the mainshock,and their vertical and horizontal components could be effectively detected,with superior detection performance in the vertical component.(2)Events with large amplitudes and long durations were better identified using the Hilbert transform,whereas those with small amplitudes,short durations,and overlapping waveforms were effectively detected using STFT.(3)A total of 67.7%of the stations successfully recorded all events,demonstrating strong observational reliability.The very low frequency earthquakes exhibited distinct spectral peaks within a relatively low-frequency range(0.06-0.16 Hz),markedly differing from the frequency bands of natural earthquakes.The event with the largest amplitude occurred 18 h before the mainshock,followed by an increasing frequency of events accompanied by heightened small earthquake activity.This pattern may reflect a gradual release of crustal stress through very low frequency earthquakes and minor earthquakes until the occurrence of the mainshock.

关 键 词：超低频地震 希尔伯特变换 短时傅里叶变换 泸定M_(S)6.8地震 

分 类 号：P315.3[天文地球—地震学]