基于小波变换的2013年芦山M_S7.0地震前姑咱台钻孔应变异常时频分析
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摘要
2013年4月20日芦山M_S7.0地震前,四川省姑咱台四分量YRY-4型钻孔应变仪记录到显著的高频应变畸变信号。为了避免该畸变信号的高频部分在时频演化过程中发生频率混叠现象,同时便于讨论同一研究频段内震前更早记录到的弱应变异常时段与显著应变异常时段的相关性,本文对2012年1月1日至2013年4月20日期间姑咱台的钻孔应变数据进行了时频分析,并使用时域分段的小波变换方法,在局部时频谱中提取了应变异常,分析了各应变异常的频率相关性。结果表明,研究频段内存在两个峰值频率,峰值频率附近频段内弱应变异常时段与显著应变异常时段的相关系数为0.85,统计出的无震时段与其显著应变异常时段之间的相关系数只有-0.007,且已排除远震以及外界环境带来的干扰,因此该峰值频率作为异常频率的可信度较高,由此推测四分量钻孔应变仪所记录到的两种不同程度的应变畸变信号的演化过程可能与芦山M_S7.0地震相关。
Before the 20 April 2013 Lushan M_S7.0 earthquake,a significant high frequency strain distortion signal has been recorded by the four-component YRY-4 borehole strainmeter at Guzan station in Sichuan Province. In order to avoid the frequency aliasing phenomenon of the high frequency part of the distortion signal in time-frequency evolution process in the same spectrum,and for the purpose of discussing the correlation between the weak strain anomaly period recorded earlier and the significant strain anomaly period in the same studied frequency band before the earthquake,this paper carried out time-frequency analysis on the borehole strain data of Guzan station during the period from 1 January 2012 to 20 April 2013 by using the continuous wavelet transform method. The results show that there are two peak frequencies in the studied frequency band,the correlation coefficient between the weak strain period and significant strain anomalous period near the peak frequency reach 0.85,and the correlation coefficient between aseismic period and significant strain anomalous period is only-0.007. Therefore,the peak frequencies is highly reliable as the anomalous frequency,and the evolution of two kinds of deformed strain signals recorded by four-component borehole strain gauge may be related to Lushan M_S7.0 earthquake.
Before the 20 April 2013 Lushan M_S7.0 earthquake,a significant high frequency strain distortion signal has been recorded by the four-component YRY-4 borehole strainmeter at Guzan station in Sichuan Province. In order to avoid the frequency aliasing phenomenon of the high frequency part of the distortion signal in time-frequency evolution process in the same spectrum,and for the purpose of discussing the correlation between the weak strain anomaly period recorded earlier and the significant strain anomaly period in the same studied frequency band before the earthquake,this paper carried out time-frequency analysis on the borehole strain data of Guzan station during the period from 1 January 2012 to 20 April 2013 by using the continuous wavelet transform method. The results show that there are two peak frequencies in the studied frequency band,the correlation coefficient between the weak strain period and significant strain anomalous period near the peak frequency reach 0.85,and the correlation coefficient between aseismic period and significant strain anomalous period is only-0.007. Therefore,the peak frequencies is highly reliable as the anomalous frequency,and the evolution of two kinds of deformed strain signals recorded by four-component borehole strain gauge may be related to Lushan M_S7.0 earthquake.
引文
池顺良,刘琦,池毅,邓涛,廖成旺,阳光,张贵萍,陈洁.2013.2013年芦山MS7.0地震的震前及临震应变异常[J].地震学报,35(3):296-303.Chi S L,Liu Q,Chi Y,Deng T,Liao C W,Yang G,Zhang G P,Chen J.2013.Borehole strain anomalies before the 20 April2013 Lushan MS7.0 earthquake[J].Acta Seismologica Sinica,35(3):296-303(in Chinese).
池顺良,张晶,池毅.2014.汶川、鲁甸、康定地震前应变数据由自洽到失洽的转变与地震成核[J].国际地震动态,(12):3-13.Chi S L,Zhang J,Chi Y.2014.Failure of self-consistent strain data before Wenchuan,Ludian and Kangding earthquakes and its relation with earthquake nucleation[J].Recent Developments in World Seismology,(12):3-13(in Chinese).
崔锦泰.1995.小波分析导论[M].西安:西安交通大学出版社:129-148.Cui C K.1995.An Introduction to Wavelet Analysis[M].Xi’an:Xi’an Jiaotong University Press:129-148(in Chinese).
廖盈春.2007.小波变换在固体潮观测资料处理中的应用[D].武汉:华中科技大学:16-25.Liao Y C.2007.The Tidal Signal Processing Based on Wavelet Analysis[D].Wuhan:Huazhong University of Science and Technology:16-25(in Chinese).
刘琦,张晶.2011.S变换在汶川地震前后应变变化分析中的应用[J].大地测量与地球动力学,31(4):6-9.Liu Q,Zhang J.2011.Application of S transform in analysis of strain changes before and after Wenchuan earthquake[J].Journal of Geodesy and Geodynamics,31(4):6-9(in Chinese).
刘琦,张晶,池顺良,闫伟.2014.2013年芦山MS7.0地震前后姑咱台四分量钻孔应变时频特征分析[J].地震学报,36(5):770-779.Liu Q,Zhang J,Chi S L,Yan W.2014.Time-frequency characteristics of four-component borehole strain at Guzan station before and after 2013 Lushan MS7.0 earthquake[J].Acta Seismologica Sinica,36(5):770-779(in Chinese).
牛安福,张凌空,闫伟,吉平.2011.中国钻孔应变观测能力及在地震预报中的应用[J].大地测量与地球动力学,31(2):48-52.Niu A F,Zhang L K,Yan W,Ji P.2011.Borehole strain measurement and application to earthquake prediction in China[J].Journal of Geodesy and Geodynamics,31(2):48-52(in Chinese).
钱世锷.2005.时频变换与小波变换导论[M].北京:机械工业出版社:68-82.Qian S E.2005.The Time-Frequency Transform and Wavelet Transforms[M].Beijing:China Machine Press:6 8-8 2(in Chinese).
邱泽华.2004.钻孔应变观测点到地面载荷干扰源最小“安静”距离的理论分析[J].岩石力学与工程学报,23(23):4063-4067.Qiu Z H.2004.Theoretic studies on the shortest‘quiet’distance between borehole strain observatory site and surficial mechanical disturbance sources[J].Chinese Journal of Rock Mechanics and Engineering,23(23):4063-4067(in Chinese).
邱泽华,周龙寿,池顺良.2009.用超限率分析法研究汶川地震的前兆应变变化[J].大地测量与地球动力学,29(4):1-4.Qiu Z H,Zhou L S,Chi S L.2009.Study on precursory strain changes of Wenchuan earthquake with ORA method[J].Journal of Geodesy and Geodynamics,29(4):1-4(in Chinese).
邱泽华,杨光,唐磊,郭燕萍,张宝红.2015.芦山MS7.0地震前姑咱台钻孔应变观测异常[J].大地测量与地球动力学,35(1):158-161.Qiu Z H,Yang G,Tang L,Guo Y P,Zhang B H.2015.Abnormal strain changes prior to the M7.0 Lushan earthquake observed by a borehole strainmeter at Guzan[J].Journal of Geodesy and Geodynamics,35(1):158-161(in Chinese).
徐伟民,陈石,卢红艳.2015.台站连续重力信号的差分方法原理及理论验证[J].国际地震动态,(9):89.Xu W M,Chen S,Lu H Y.2015.The principle and theoretical verification of the differential method of continuous gravity signal in station[J].Recent Developments in World Seismology,(9):89(in Chinese).
池顺良,张晶,池毅.2014.汶川、鲁甸、康定地震前应变数据由自洽到失洽的转变与地震成核[J].国际地震动态,(12):3-13.Chi S L,Zhang J,Chi Y.2014.Failure of self-consistent strain data before Wenchuan,Ludian and Kangding earthquakes and its relation with earthquake nucleation[J].Recent Developments in World Seismology,(12):3-13(in Chinese).
崔锦泰.1995.小波分析导论[M].西安:西安交通大学出版社:129-148.Cui C K.1995.An Introduction to Wavelet Analysis[M].Xi’an:Xi’an Jiaotong University Press:129-148(in Chinese).
廖盈春.2007.小波变换在固体潮观测资料处理中的应用[D].武汉:华中科技大学:16-25.Liao Y C.2007.The Tidal Signal Processing Based on Wavelet Analysis[D].Wuhan:Huazhong University of Science and Technology:16-25(in Chinese).
刘琦,张晶.2011.S变换在汶川地震前后应变变化分析中的应用[J].大地测量与地球动力学,31(4):6-9.Liu Q,Zhang J.2011.Application of S transform in analysis of strain changes before and after Wenchuan earthquake[J].Journal of Geodesy and Geodynamics,31(4):6-9(in Chinese).
刘琦,张晶,池顺良,闫伟.2014.2013年芦山MS7.0地震前后姑咱台四分量钻孔应变时频特征分析[J].地震学报,36(5):770-779.Liu Q,Zhang J,Chi S L,Yan W.2014.Time-frequency characteristics of four-component borehole strain at Guzan station before and after 2013 Lushan MS7.0 earthquake[J].Acta Seismologica Sinica,36(5):770-779(in Chinese).
牛安福,张凌空,闫伟,吉平.2011.中国钻孔应变观测能力及在地震预报中的应用[J].大地测量与地球动力学,31(2):48-52.Niu A F,Zhang L K,Yan W,Ji P.2011.Borehole strain measurement and application to earthquake prediction in China[J].Journal of Geodesy and Geodynamics,31(2):48-52(in Chinese).
钱世锷.2005.时频变换与小波变换导论[M].北京:机械工业出版社:68-82.Qian S E.2005.The Time-Frequency Transform and Wavelet Transforms[M].Beijing:China Machine Press:6 8-8 2(in Chinese).
邱泽华.2004.钻孔应变观测点到地面载荷干扰源最小“安静”距离的理论分析[J].岩石力学与工程学报,23(23):4063-4067.Qiu Z H.2004.Theoretic studies on the shortest‘quiet’distance between borehole strain observatory site and surficial mechanical disturbance sources[J].Chinese Journal of Rock Mechanics and Engineering,23(23):4063-4067(in Chinese).
邱泽华,周龙寿,池顺良.2009.用超限率分析法研究汶川地震的前兆应变变化[J].大地测量与地球动力学,29(4):1-4.Qiu Z H,Zhou L S,Chi S L.2009.Study on precursory strain changes of Wenchuan earthquake with ORA method[J].Journal of Geodesy and Geodynamics,29(4):1-4(in Chinese).
邱泽华,杨光,唐磊,郭燕萍,张宝红.2015.芦山MS7.0地震前姑咱台钻孔应变观测异常[J].大地测量与地球动力学,35(1):158-161.Qiu Z H,Yang G,Tang L,Guo Y P,Zhang B H.2015.Abnormal strain changes prior to the M7.0 Lushan earthquake observed by a borehole strainmeter at Guzan[J].Journal of Geodesy and Geodynamics,35(1):158-161(in Chinese).
徐伟民,陈石,卢红艳.2015.台站连续重力信号的差分方法原理及理论验证[J].国际地震动态,(9):89.Xu W M,Chen S,Lu H Y.2015.The principle and theoretical verification of the differential method of continuous gravity signal in station[J].Recent Developments in World Seismology,(9):89(in Chinese).