应用微动H/V谱比法和台阵技术探测场地响应和浅层速度结构
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摘要
为了快速而且廉价地获取北京市详细的场地响应和浅层速度结构,应用于地震动模拟和地震灾害预防,我们开展了微动观测技术和处理方法研究.本文利用2007年夏季北京五棵松地区进行的几个微动观测实验数据,使用单台H/V谱比法分析场地的卓越频率及其对应的放大系数,并对比了不同地震仪和观测时间对H/V曲线的影响;应用高分辨率F-K频谱分析方法从微动台阵数据中得到Rayleigh波的频散曲线并使用邻域算法反演出浅层速度结构.H/V结果表明该地区卓越频率在2.1～2.2 Hz之间,对应的放大系数下限约为3;利用微动H/V方法得到的场地卓越频率具有较高的稳定性.微动台阵反演结果给出了比较合理的波阻抗界面深度和层平均速度结构,认为地下80多米处的波阻抗界面是决定场地卓越频率和其场地放大系数的主要界面.本研究表明微动技术应用于评估城市地震场地响应和浅层速度结构是可行且易于实施的.
To rapidly and economically assess the detailed seismic site effects and near surface velocity structures which are crucial for accurate strong motion simulation and efficient seismic hazard prevention,we conducted microtremor array observations and subsequent data processing for the urban areas of the Beijing city.In this paper,using the data collected from several microtremor observation experiments at Wukesong area in the summer of 2007,we estimated the predominant frequencies and their amplification factors of this site with the H/V spectral ratio method.We also investigated the effects of different seismometers and observation times on the H/V spectra curve.Furthermore we retrieved the Rayleigh wave dispersion curve by applying the high-resolution F-K spectral analysis method to the microtremor array observation data and inverted for the subsurface velocity structure using the neighborhood algorithm.The H/V results show that the predominant frequencies in the Wukesong area are about 2.1～2.2 Hz with the lower limit of the amplification factor about 3.The predominant frequencies obtained from the microtremor H/V analysis are stable in this study.The inversion results from the microtremor array data reveal a reasonable subsurface velocity structure in terms of both impedance interface depths and average layer velocities,and suggest that an interface at about 80 meter depth makes the primary contribution to the predominant frequency and the corresponding amplification factor of this site.This study demonstrates that the microtremor technology is a practical and feasible way to assess the seismic site effect and near surface velocity structure at an urban site.
To rapidly and economically assess the detailed seismic site effects and near surface velocity structures which are crucial for accurate strong motion simulation and efficient seismic hazard prevention,we conducted microtremor array observations and subsequent data processing for the urban areas of the Beijing city.In this paper,using the data collected from several microtremor observation experiments at Wukesong area in the summer of 2007,we estimated the predominant frequencies and their amplification factors of this site with the H/V spectral ratio method.We also investigated the effects of different seismometers and observation times on the H/V spectra curve.Furthermore we retrieved the Rayleigh wave dispersion curve by applying the high-resolution F-K spectral analysis method to the microtremor array observation data and inverted for the subsurface velocity structure using the neighborhood algorithm.The H/V results show that the predominant frequencies in the Wukesong area are about 2.1～2.2 Hz with the lower limit of the amplification factor about 3.The predominant frequencies obtained from the microtremor H/V analysis are stable in this study.The inversion results from the microtremor array data reveal a reasonable subsurface velocity structure in terms of both impedance interface depths and average layer velocities,and suggest that an interface at about 80 meter depth makes the primary contribution to the predominant frequency and the corresponding amplification factor of this site.This study demonstrates that the microtremor technology is a practical and feasible way to assess the seismic site effect and near surface velocity structure at an urban site.
引文
[1] Borcherdt R D.Effects of local geology on ground motion near San Francisco Bay.Bull Seism Soc Am,1970,60:29-81
[2] Boatwright J,Fletcher J B,Fumal T E.A general inversion scheme for source,site,and propagation characteristics using multiply recorded sets of moderate sized earthquakes.Bull Seism Soc Am,1991,81:1754-1782
[3] Nogoshi M,Igarashi T.On the amplitude characteristics of microtremor (part 2) .J.Seismol Soc Japan.1971,24:26-40
[4] Nakamura Y. A method for dynamic characteristics estimation of subsurface using microtremor on the ground surface.Quarterly Report Railway Tech Res Inst,1989,30(1) :25-30
[5] Nakamura Y.Clear identification of fundamental idea of Nakamura's technique and its applications.Proceedings of the 12th World Conference on Earthquake Engineering,Auckland,New Zealand,2000
[6] Lermo J,Chavez-Garcia F J.Site effect evaluation at Mexico city:dominant period and relative amplication from strong motion and microtremor records.Soil Dyn and Earthq Eng,1994,13:413-423
[7] Seekins L C,Wennerberg L,Marghereti L,et al.Site amplification at five locations in San Fransico,California:a comparison of S waves,codas,and microtremors.Bull Seism Soc Am,1996,86:627-635
[8] Tokimatsu K.Geotechnical site characterization using surface waves.Proceedings of the First International Conference on Earthquake Geotechnical Engineering,1997,3:1333-1368
[9] Arai H,Tokimatsu K.Evaluation of local site effects based on microtremor H/V spectra.Proceeding of the Second International Symposium on the Effects of Surface Geology on Seismic Motion,Yokohama,Japan,1998,2:673-680
[10] Bard P Y,Sesame Participants.The SESAME project:an overview and main results.Proceedings of the 13th World Conference on Earthquake Engineering,Vancouver,2004,Paper 2207
[11] Lachet C,Bard P Y.Numerical and theoretical investigations on the possibilities and limitations of Nakamura's technique.J.Phys Earth,1994,42:377-397
[12] Bonnefoy-Claudet S,Cornou C,Bard P Y,Cotton F,et al.H/V ratio:a tool for site effects evaluation.Results from 1D noise simulations.Geophys J.Int,2006,167:827--837
[13] Bonnefoy Claudet S,Cotton F,Bard P Y,et al.Robustness of the H/V ratio peak frequency to estimate 1D resonance frequency.Third International Symposium on the Effects of Surface Geology on Seismic Motion,Grenoble,France,2006,Paper Number 85
[14] Lacoss R T,Kelly E J,Toksoz M N.Estimation of seismic noise structure using arrays.Geophysics,1969,34:21-38
[15] Capon J.High-resolution frequency-wavenumber spectrum analysis.Proc IEEE,1969,57:1408-1418
[16] Aki K.Space and time spectra of stationary stochastic waves with special reference to microtremors.Bull Earthq Res Inst,1957,35:415-456
[17] Bettig B,Bard P Y,Scherbaum F,Riepl J,et al.Analysis of dense array noise measurements using the modied spatial auto-correlation method (SPAC)-Application to the Grenoble area.Bolletino di Geosica Teorica ed Applicata,2001,42:281-304
[18] Ling S,Okada H.An extended use of the spatial autocorrelation method for the estimation of structure using microtremors.Proc.of the 89th SEGJ Conference,Nagoya (in Japanese),Japan,1993． 44-48
[19] Cho I,Tada T,Shinozaki Y.Centerless circular array method:Inferring phase velocities of Rayleigh waves in broad wavelength ranges using microtremor records.J.Geophys Res,2006,111,B09315,doi:10． 1029/2005JB004235
[20] Shapiro N M,Campillo M,Stehly L,Ritzwoller M H.High-resolution surface-wave tomography from ambient seismic noise.Science,2005,307:1615-1618
[21] Chavez-Garcia F J,Rodriguez M.The correlation of microtremors:empirical limits and relations between results in frequency and time domains.Geophys J Int,2007,171:657-664
[22] 杨成林.瑞雷波勘探.北京:地质出版社,1993 Yang C L.Rayleigh Wave Exploration (in Chinese).Beijing:Geological Puhlishing House,1993
[23] 许建聪,孙红月.地脉动作用下的岩土动力响应研究.振动工程学报,2004,17(2) :147～150 Xu J C,Sun H Y.Study on dynamical response of ground soil to micro-tremor.J.of Vibration Engineering (in Chinese),2004,17(2) :147-150
[24] 陶夏新,刘曾武,郭明珠等.工程场地条件评定中的地脉动研 究.地震工程与工程振动,2001,21(4) :18～23 Tao X X,Liu Z W,Guo M Z,et el.A review of microtremor study in engineering site rating.Earthquake Engineering and Engineering Vibration (in Chinese),2001,21(4) :18-23
[25] 师黎静,陶夏新,赵纪生.地脉动台阵方法的有效性分析.岩石力学与工程学报,2006,25(8) :1683～1690 Shi L J,Tao X X,Zhao J S.Validataion of mierotremors array method.Chinese Journal nf Rock Mechanics and Engineering (in Chinese),2006,25(8) :1683-1690
[26] 何正勤,丁志峰.贾辉等.用微动中的面波信息探测地壳浅部的速度结构.地球物理学报,2007,50(2) :492～498 He Z Q,Ding Z F,Jia H,et al.To determine the velocity structure of shallow crust with surface wave information in microtremors.Chinese J.Geophys.(in Chinese),2007,50(2) :492-498
[27] Konno K,Ohmachi T. Ground motion characteristics estimated from spectral ratio between horizontal and vertical components of microtremor.Bull Seism Soc Am,1997,88:228-241
[28] Atakan K,Dural A M,Theodulidis N,Guillier B,et el.The H/V spectral ratio technique:experimental conditions,data processing and empirical reliability assessment,13th World Conference in Earthquake Engineering,Vancouver,2004． Paper 2268
[29] Wathelet M.Array recordings of ambient vibrations:surface-wave inversion.[Ph.D.thesis],Universit'e de Li'ege,Belgium,2005
[30] Wathelet M,Jongmans D,Ohrnberger M,et al.Array performances for ambient vibratious on a shallow structure and consequences over V_s inversion.Journal of Seismology,2008,12:1-19
[31] Sambridge M.Geophysical inversion with a neighbourhood algorithm I.Searching a parameter space.Geophys J.Int,1999,103:4839-4878
[32] Wathelet M,Jongmans D,Ohrnberger M.Surface wave inversion using a direct search algorithm and its application to ambient vibration measurements.Near Surface Geophysics,2004,2:211--221
[33] Parolai S,Galiana-Merino J J.Effect of Transient Seismic Noise on Estimates of H/V Spectral Ratios.Bull Seism Soc Am,2006,96:228-236,doi:10． 1785/0120050084
[34] Asten M W,Henstridge J D.Array estimators and use of microseisms for reconnaissance of sedimentary basins.Geophysics.1984． 49:1828-1837
[2] Boatwright J,Fletcher J B,Fumal T E.A general inversion scheme for source,site,and propagation characteristics using multiply recorded sets of moderate sized earthquakes.Bull Seism Soc Am,1991,81:1754-1782
[3] Nogoshi M,Igarashi T.On the amplitude characteristics of microtremor (part 2) .J.Seismol Soc Japan.1971,24:26-40
[4] Nakamura Y. A method for dynamic characteristics estimation of subsurface using microtremor on the ground surface.Quarterly Report Railway Tech Res Inst,1989,30(1) :25-30
[5] Nakamura Y.Clear identification of fundamental idea of Nakamura's technique and its applications.Proceedings of the 12th World Conference on Earthquake Engineering,Auckland,New Zealand,2000
[6] Lermo J,Chavez-Garcia F J.Site effect evaluation at Mexico city:dominant period and relative amplication from strong motion and microtremor records.Soil Dyn and Earthq Eng,1994,13:413-423
[7] Seekins L C,Wennerberg L,Marghereti L,et al.Site amplification at five locations in San Fransico,California:a comparison of S waves,codas,and microtremors.Bull Seism Soc Am,1996,86:627-635
[8] Tokimatsu K.Geotechnical site characterization using surface waves.Proceedings of the First International Conference on Earthquake Geotechnical Engineering,1997,3:1333-1368
[9] Arai H,Tokimatsu K.Evaluation of local site effects based on microtremor H/V spectra.Proceeding of the Second International Symposium on the Effects of Surface Geology on Seismic Motion,Yokohama,Japan,1998,2:673-680
[10] Bard P Y,Sesame Participants.The SESAME project:an overview and main results.Proceedings of the 13th World Conference on Earthquake Engineering,Vancouver,2004,Paper 2207
[11] Lachet C,Bard P Y.Numerical and theoretical investigations on the possibilities and limitations of Nakamura's technique.J.Phys Earth,1994,42:377-397
[12] Bonnefoy-Claudet S,Cornou C,Bard P Y,Cotton F,et al.H/V ratio:a tool for site effects evaluation.Results from 1D noise simulations.Geophys J.Int,2006,167:827--837
[13] Bonnefoy Claudet S,Cotton F,Bard P Y,et al.Robustness of the H/V ratio peak frequency to estimate 1D resonance frequency.Third International Symposium on the Effects of Surface Geology on Seismic Motion,Grenoble,France,2006,Paper Number 85
[14] Lacoss R T,Kelly E J,Toksoz M N.Estimation of seismic noise structure using arrays.Geophysics,1969,34:21-38
[15] Capon J.High-resolution frequency-wavenumber spectrum analysis.Proc IEEE,1969,57:1408-1418
[16] Aki K.Space and time spectra of stationary stochastic waves with special reference to microtremors.Bull Earthq Res Inst,1957,35:415-456
[17] Bettig B,Bard P Y,Scherbaum F,Riepl J,et al.Analysis of dense array noise measurements using the modied spatial auto-correlation method (SPAC)-Application to the Grenoble area.Bolletino di Geosica Teorica ed Applicata,2001,42:281-304
[18] Ling S,Okada H.An extended use of the spatial autocorrelation method for the estimation of structure using microtremors.Proc.of the 89th SEGJ Conference,Nagoya (in Japanese),Japan,1993． 44-48
[19] Cho I,Tada T,Shinozaki Y.Centerless circular array method:Inferring phase velocities of Rayleigh waves in broad wavelength ranges using microtremor records.J.Geophys Res,2006,111,B09315,doi:10． 1029/2005JB004235
[20] Shapiro N M,Campillo M,Stehly L,Ritzwoller M H.High-resolution surface-wave tomography from ambient seismic noise.Science,2005,307:1615-1618
[21] Chavez-Garcia F J,Rodriguez M.The correlation of microtremors:empirical limits and relations between results in frequency and time domains.Geophys J Int,2007,171:657-664
[22] 杨成林.瑞雷波勘探.北京:地质出版社,1993 Yang C L.Rayleigh Wave Exploration (in Chinese).Beijing:Geological Puhlishing House,1993
[23] 许建聪,孙红月.地脉动作用下的岩土动力响应研究.振动工程学报,2004,17(2) :147～150 Xu J C,Sun H Y.Study on dynamical response of ground soil to micro-tremor.J.of Vibration Engineering (in Chinese),2004,17(2) :147-150
[24] 陶夏新,刘曾武,郭明珠等.工程场地条件评定中的地脉动研 究.地震工程与工程振动,2001,21(4) :18～23 Tao X X,Liu Z W,Guo M Z,et el.A review of microtremor study in engineering site rating.Earthquake Engineering and Engineering Vibration (in Chinese),2001,21(4) :18-23
[25] 师黎静,陶夏新,赵纪生.地脉动台阵方法的有效性分析.岩石力学与工程学报,2006,25(8) :1683～1690 Shi L J,Tao X X,Zhao J S.Validataion of mierotremors array method.Chinese Journal nf Rock Mechanics and Engineering (in Chinese),2006,25(8) :1683-1690
[26] 何正勤,丁志峰.贾辉等.用微动中的面波信息探测地壳浅部的速度结构.地球物理学报,2007,50(2) :492～498 He Z Q,Ding Z F,Jia H,et al.To determine the velocity structure of shallow crust with surface wave information in microtremors.Chinese J.Geophys.(in Chinese),2007,50(2) :492-498
[27] Konno K,Ohmachi T. Ground motion characteristics estimated from spectral ratio between horizontal and vertical components of microtremor.Bull Seism Soc Am,1997,88:228-241
[28] Atakan K,Dural A M,Theodulidis N,Guillier B,et el.The H/V spectral ratio technique:experimental conditions,data processing and empirical reliability assessment,13th World Conference in Earthquake Engineering,Vancouver,2004． Paper 2268
[29] Wathelet M.Array recordings of ambient vibrations:surface-wave inversion.[Ph.D.thesis],Universit'e de Li'ege,Belgium,2005
[30] Wathelet M,Jongmans D,Ohrnberger M,et al.Array performances for ambient vibratious on a shallow structure and consequences over V_s inversion.Journal of Seismology,2008,12:1-19
[31] Sambridge M.Geophysical inversion with a neighbourhood algorithm I.Searching a parameter space.Geophys J.Int,1999,103:4839-4878
[32] Wathelet M,Jongmans D,Ohrnberger M.Surface wave inversion using a direct search algorithm and its application to ambient vibration measurements.Near Surface Geophysics,2004,2:211--221
[33] Parolai S,Galiana-Merino J J.Effect of Transient Seismic Noise on Estimates of H/V Spectral Ratios.Bull Seism Soc Am,2006,96:228-236,doi:10． 1785/0120050084
[34] Asten M W,Henstridge J D.Array estimators and use of microseisms for reconnaissance of sedimentary basins.Geophysics.1984． 49:1828-1837
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