华北科学探测台阵背景噪声特征分析
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摘要
利用华北科学探测台阵180多个宽频带台站2007年的连续记录,得到了台站之间噪声互相关函数.通过对三个分量记录的相关运算,获得了Rayleigh波和Love波的经验格林函数,分析了其信噪比随周期的变化和高信噪比台站对的方位分布.利用经验格林函数的非对称性和聚束方法,研究了华北科学探测台阵地震噪声的方位分布,及其季节变化特征.尽管噪声源的分布随季节有轻微变化,但全年的分析结果表明,10-32 s周期内华北台阵的地震噪声源在各个方向上的分布近于均匀,这为利用噪声成像提供了理论前提.
Noise Cross-Correlation Function (NCF) is obtained by processing one-year ambient noise observed at over 180 broad-band stations from North China Array. All available threecomponent time series are used to extract the Rayleigh and Love waves. The Signal-to-Noise Ratio (SNR) at different periods and the azimuth distribution of the inter-station pairs with high SNR are discussed. The azimuth distributions of the ambient noise source are investigated by analyzing the beamforming output. Although seasonal variations are observed from the beamforming output, the source distribution at 10-32 s is almost uniformly distributed in all directions, which allows us to perform the following detailed tomography safely.
Noise Cross-Correlation Function (NCF) is obtained by processing one-year ambient noise observed at over 180 broad-band stations from North China Array. All available threecomponent time series are used to extract the Rayleigh and Love waves. The Signal-to-Noise Ratio (SNR) at different periods and the azimuth distribution of the inter-station pairs with high SNR are discussed. The azimuth distributions of the ambient noise source are investigated by analyzing the beamforming output. Although seasonal variations are observed from the beamforming output, the source distribution at 10-32 s is almost uniformly distributed in all directions, which allows us to perform the following detailed tomography safely.
引文
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Fang L H, Wu J P,Lu Z Y. Rayleigh wave group velociyty tomography from ambient noise in north China. Chinese J. Geophys. (in Chinese) , 2009,52(3) :663-671
[16] Bensen G D, Ritzwoller M H, Shapiro N M. Broadband ambient noise surface wave tomography across the United States. J. Geophys. Res. ,2008,113,B05306, doi:10． 1029/ 2007JB005248
[17] Gu Y J, Dublanko C, Lerner-Lam A, et al. Probing the sources of ambient seismic noise near the coasts of southern Italy. Geophys. Res. Lett. ,2007,34,L22315, doi:10． 1029/ 2007GL031967
[18] Gerstoft P, Tanimoto T. A year of microseisms in southern California.Geophys. Res. Lett. ,2007,34,L20304, doi: 10． 1029/2007GL031091
[19] Harmon N, Gerstoft P, Rychert C A, et al. Phase velocities from seismic noise using beamforming and cross correlation in Costa Rica and Nicaragua. Geophys. Res. Lett. ,2008,35,L19303, doi:10． 1029/2008GL035387．
[20] Nishida K, Kawakatsu H, Obara K. Three-dimensional crustal S wave velocity sturcture in Japan using microseismic data recorded by Hi-net tilt-meters. J. Geophys. Res. ,2008,113,B10302, doi:10． 1029/2007JB005395
[21] Rost S, Thomas C. Array seismology: methods andapplications. Rev. Geophys. , 2002, 40(3) :1008, doi: 10． 1029/2000RG000100
[2] Sabra K G, Gerstoft P, Roux P, et al. Extracting time-domain Green s function estimates from ambient seismic noise. Geophys. Res. Lett. ,2005,32,L03310, doi:10． 1029/ 2004GL021862
[3] Campillo M, Paul A. Long-range correlations in the diffuse seismic coda. Science,2003,299:547-549
[4] Weaver R L. Information from Seismic Noise. Science, 2005,37． 1568-1569
[5] Bensen G. D, Ritzwoller M H, Barmin M P, et al. Processing seismic ambient noise data to obtain reliable broadband surface waves dispersion measurements. Geophys. J.Int. , 2007, 169: 1239-1260, doi:10． 111/j. 1365-246X.2007． 03374． x
[6] Lin F C, Moschetti M P, Ritzwoller M H. Surface wave tomography of the western United States from ambient seismic noise: Rayleigh and Love wve phase velocity maps. Geophys.J. Int. ,2008,173: 281-298, doi:10． 111/j. 1365-246X. 2008． 03720． x
[7] Shapiro N M, Campillo M, Stehly L, et al. High-Resolution surface-wave tomography from ambient seismic noise. Science, 2005,307:1615-1618
[8] Lin F C, Ritzwoller M H, Townend J, et al. Ambient noise Rayleigh wave tomography of New Zealand. Geophys. J.Int. ,2007,170:649-666
[9] Yang Y J, Ritzwoller M H, Levshin A L, Shapiro N M. Ambient noise Rayleigh wave tomography across Europe. Geophys. J. Int. , 2007, 168:259-274
[10] Roux P, Sabra K G, Gerstoft P, et al. P-waves from crosscorrelation of seismic noise. Geophys. Res. Lett., 2005, 32,L19303, doi:10． 1029/2005GL023803
[11] Webb S C. The Earth's 'hum' is driven by ocean waves over the continental shelves. Nature, 2007,445:754-756
[12] Stehly L, Campillo M, Shapiro N M. A study of the seismic noise from its long-range correlation properties. J. Geophys. Res. , 2006,111,B10306,doi:10． 1029/2005JB004237
[13] Chevrot S, Sylvander M, Benahmed S, et al. Source location of secondary microseisms in western Europe:Evidence for both coastal and pelagic sources. J. Geophys. Res. ,2007,112,B11301, doi:10． 1029/2007/JB005059
[14] Yang Y, Ritzwoller H. Characteristics of ambient seismic noise as a source for surface wave tomography, Geochem. Geophys. Geosyst. , 2008, 9, Q02008, doi: 10． 1029/2007GC001814
[15] 房立华,吴建平,吕作勇.华北地区基于噪声的Rayleigh面波群速度层析成像.地球物理学报,2009,52(3) :663-671
Fang L H, Wu J P,Lu Z Y. Rayleigh wave group velociyty tomography from ambient noise in north China. Chinese J. Geophys. (in Chinese) , 2009,52(3) :663-671
[16] Bensen G D, Ritzwoller M H, Shapiro N M. Broadband ambient noise surface wave tomography across the United States. J. Geophys. Res. ,2008,113,B05306, doi:10． 1029/ 2007JB005248
[17] Gu Y J, Dublanko C, Lerner-Lam A, et al. Probing the sources of ambient seismic noise near the coasts of southern Italy. Geophys. Res. Lett. ,2007,34,L22315, doi:10． 1029/ 2007GL031967
[18] Gerstoft P, Tanimoto T. A year of microseisms in southern California.Geophys. Res. Lett. ,2007,34,L20304, doi: 10． 1029/2007GL031091
[19] Harmon N, Gerstoft P, Rychert C A, et al. Phase velocities from seismic noise using beamforming and cross correlation in Costa Rica and Nicaragua. Geophys. Res. Lett. ,2008,35,L19303, doi:10． 1029/2008GL035387．
[20] Nishida K, Kawakatsu H, Obara K. Three-dimensional crustal S wave velocity sturcture in Japan using microseismic data recorded by Hi-net tilt-meters. J. Geophys. Res. ,2008,113,B10302, doi:10． 1029/2007JB005395
[21] Rost S, Thomas C. Array seismology: methods andapplications. Rev. Geophys. , 2002, 40(3) :1008, doi: 10． 1029/2000RG000100
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