淮安地震台沙层应力仪器观测数据变化的特征分析
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摘要
用小波变换和傅里叶变换的分析方法对2009年5月至2012年6月淮安沙层应力数据进行频谱分析。发现:淮安台沙层仪器所记录数据中含有多个频率成份,其中低频信号频率以1.157 4×10-5 Hz附近信号最强,在2.314 8×10-5 Hz附近次之,高频信号频率在0.25～0.45Hz之间。低频信号反映在日、月等引潮力的作用下固体地球产生的周期性潮汐变化的地壳形变特征;高频信号更多的反映地壳应力变化特征。淮安沙层应力观测数值变化不仅与其他沙层应力台站有相同变化形态和一致的年变规律,还与地震活动有较好的对应关系。沙层应力数据变化能反映大地震从孕育到发生的完整过程,一般具有上升、平稳、下降、回升发震等几个阶段。
The sand bed stress instrument is a precursory observation instrument used to transmit crustal stress signals via particle media,which entails sensors buried in the sand underground to receive the stress generated by the sand movement surrounding the sensor.It is widely accepted that the collision between sand grains can lead to stress changes in the Earth's crust and may affect the direction and numerical value of the crustal stress.To demonstrate the manner in which data recorded by the sand bed stress instrument reflects the characteristics of the underground stress,we used Fourier transform and via wavelet analysis to study the stress data of a sand bed in Huai'an,Jiangsu province,from May 2009 to June 2012.We detected a number of multiple frequency components recorded in the sand bed stress observation instrument,among which the frequency at 1.1574x10-5 Hz was the strongest signal,followed by 2.314 8x10-5 Hz.These frequency components included in the sand bed stress data clearly show the periodic tidal variations of the solid Earth under the tidal forces of the sun and the moon.A tidal cycle consists mainly of one-day waves and half-day waves;the former have the greatest influence on periodic tidal variations.In addition,we compared the stress data of sand bed in Huai'an with those in Xiji,Beijing,and Putian,Fujian province,to determine that despite the differences in geological environments,they exhibited the same trend of rise and fall in value,which obviously show a synchronous change and a consistent annual variation.The changes in stress data from the Huai'an station create an effective model for studying seismic activity.Such changes reflect the entire processes of major earthquake seismogenic phenomena,which include loading,rallying,unloading,and rising,in addition to higher frequency signal loading or unloading prior to a major earthquake with a frequency between 0.3 and 0.4.On the contrary,when a moderate earthquake occurs,the sand beds near seismic stations exhibit short stress seismogenic phenomena,which includes loading,unloading,and rising.Moreover,the sand bed stress data curve shows abnormal fluctuation changes in waveforms.
The sand bed stress instrument is a precursory observation instrument used to transmit crustal stress signals via particle media,which entails sensors buried in the sand underground to receive the stress generated by the sand movement surrounding the sensor.It is widely accepted that the collision between sand grains can lead to stress changes in the Earth's crust and may affect the direction and numerical value of the crustal stress.To demonstrate the manner in which data recorded by the sand bed stress instrument reflects the characteristics of the underground stress,we used Fourier transform and via wavelet analysis to study the stress data of a sand bed in Huai'an,Jiangsu province,from May 2009 to June 2012.We detected a number of multiple frequency components recorded in the sand bed stress observation instrument,among which the frequency at 1.1574x10-5 Hz was the strongest signal,followed by 2.314 8x10-5 Hz.These frequency components included in the sand bed stress data clearly show the periodic tidal variations of the solid Earth under the tidal forces of the sun and the moon.A tidal cycle consists mainly of one-day waves and half-day waves;the former have the greatest influence on periodic tidal variations.In addition,we compared the stress data of sand bed in Huai'an with those in Xiji,Beijing,and Putian,Fujian province,to determine that despite the differences in geological environments,they exhibited the same trend of rise and fall in value,which obviously show a synchronous change and a consistent annual variation.The changes in stress data from the Huai'an station create an effective model for studying seismic activity.Such changes reflect the entire processes of major earthquake seismogenic phenomena,which include loading,rallying,unloading,and rising,in addition to higher frequency signal loading or unloading prior to a major earthquake with a frequency between 0.3 and 0.4.On the contrary,when a moderate earthquake occurs,the sand beds near seismic stations exhibit short stress seismogenic phenomena,which includes loading,unloading,and rising.Moreover,the sand bed stress data curve shows abnormal fluctuation changes in waveforms.
引文
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[3]万永革.MATLAB数字信号处理实例教程[M].北京:防灾技术高等专科学校,2004:42-152.WAN Yong-ge.Tutorial Examples in Matlab Digital SignalProcessing[M].Beijing:Institute of Disaster Prevention Scine-ce and Technology,2004:42-152
[4]董长虹,高志,余萧海.Matlab小波分析工具箱原理与应用[M].北京:国防工业出版社,2005:2-42.DONG Chang-hong,GAO Zhi,YU Xiao-hai.Matlab Tool-box's Theory and Application in Wavelet Analysis[M].Bei-jing:National Defense Industry Press,2005,2-42
[5]冯锐.地倾斜与地[M].北京:地震出版社,1978:18.FENG Rui.Crustal Tilt and Earthquake[M].Beijing:Seismo-logical Press,1978:18.
[6]Reid H F.The California Earthquake of April 18,1906.(2)The Mechanics of the Earthquake[R].Carneqie Institution ofWashington D C,1910:192.
[7]谢觉民.唐山地震地壳弹性回跳的某些特征[J].地震研究,1984,7(2):137-145.XIE Jue-min.Some Features of Crustal Elastic Rebound of theTangshan Earthquake[J].Journal of Seismological Research,1984,17(2):137-144.
[8]颜玉定,李健康,廖远群.岩石实验中的微破裂与地震的联想[J].华南地震,1996,16(1):63-65.YAN Yu-ding,LI Jian-kang,LIAO Yuan-qun.Association ofIdeas between Earthquake and Microfracture in Experiment ofRock Deformation[J].Sorth China Journal of Seismology,1996,16(1):63-65.
[9]张冬丽,周正华,陶夏新.震源破裂方式和断层性质对近场强地震动特征的影响[J].西北地震学报,2009,31(4):311-318.ZHANG Dong-li,ZHOU Zheng-hua,TAO Xia-xin.Influenceof Seismic Source Mechanism and Fault Property on Near-fieldStrong Ground Motion[J].Northwestern Seismological Jour-nal,2009,31(4):311-318.
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