基于井下摆天然地震数据测量首都圈近地表波速结构
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摘要
收集了首都圈数字化地震遥测台网58个井下摆2003—2008年记录的102次M≥3.0地震的数据.通过鉴别直达波及对应地表反射波的波形,发现两者到时差与震中矩和方位角无关.基于斯涅尔定律,分析获得了这些台站上方厚约300m浅地表土层P波和S波平均速度结构以及波速比.结果表明,首都圈区域近地表P波和S波平均速度分别约为1.6—2.0km/s和0.34—0.48km/s,波速比约为4.0—5.3.进一步对比井下深度同为247m的11个台站的数据,显示该区域P波速度和波速比均无显著横向变化.清晰的震相图也表明,土壤层没有明显的速度断层.该结果对模拟强地面运动和计算精细的地壳速度结构,以及地震工程的一些领域均有一定意义.
Firstly we collected P and S waveform data from 102 earthquakes with M≥3.0 for the period 2003 to 2008 observed at 58 borehole stations obtained from the Capital Circle Digital Seismic Telemetry Network catalog.After identifying direct wave and surface reflection wave,we found their delay time varied little despite distinct epicentral distances and azimuths.Based on Snell's law,we developed travel time lags to compute average wave velocity in about 300 meters of soil layer above each station.Our results show that near-surface P-and S-wave average velocity in Chinese capital region ranges from 1.6 to 2.0 km/s and 0.34 to 0.48 km/s respectively,vP/vS is about 4.0—5.3.Furthermore,no obvious lateral variation of P-wave velocity structure or vP/vS is observed by comparing results of 11 borehole stations with the same depth of 247 m.The clear seismic phases for both P-and S-wave suggest no significant velocity discontinuity in the soil layer.The results are useful in both the simulation of strong ground motion and the calculation of detailed velocity structure in the crust or upper mantle,as well as some areas of earthquake engineering.
Firstly we collected P and S waveform data from 102 earthquakes with M≥3.0 for the period 2003 to 2008 observed at 58 borehole stations obtained from the Capital Circle Digital Seismic Telemetry Network catalog.After identifying direct wave and surface reflection wave,we found their delay time varied little despite distinct epicentral distances and azimuths.Based on Snell's law,we developed travel time lags to compute average wave velocity in about 300 meters of soil layer above each station.Our results show that near-surface P-and S-wave average velocity in Chinese capital region ranges from 1.6 to 2.0 km/s and 0.34 to 0.48 km/s respectively,vP/vS is about 4.0—5.3.Furthermore,no obvious lateral variation of P-wave velocity structure or vP/vS is observed by comparing results of 11 borehole stations with the same depth of 247 m.The clear seismic phases for both P-and S-wave suggest no significant velocity discontinuity in the soil layer.The results are useful in both the simulation of strong ground motion and the calculation of detailed velocity structure in the crust or upper mantle,as well as some areas of earthquake engineering.
引文
卞真付,姚兰予,庞群英.2005.利用井下数字地震记录反演非弹性衰减系数震源参数和场地响应[J].西北地震学报,27(增刊):60--66.
陈棋福,刘澜波,王伟君,Eric Rohrbach.2008.利用地脉动探测北京城区的地震动场地响应[J].科学通报,53(18):2229--2235.
高玉峰,张健.2007.地震危险性分析研究[M].北京:科学出版社:86--89.
齐诚,赵大鹏,陈颙,陈棋福,王宝善.2006.首都圈地区地壳P波和S波三维速度结构及其与大地震的关系[J].地球物理学报,49(3):805--815.
沈伟森,罗艳,倪四道,崇加军,陈顒.2010.天然地震频率范围内首都圈地区近地表S波速度结构[J].地震学报,32(2):137--146.
于湘伟,陈运泰,王培德.2003.京津唐地区中上地壳三维P波速度结构[J].地震学报,25(1):1--14.
朱露培,曾融生,刘福田.1990.京津唐张地区地壳上地幔三维P波速度结构[J].地球物理学报,33(3):267--277.
Aki K.1988.Local site effects on strong ground motion[G]∥Earthquake Engineering and Soil DynamicsⅡ:RecentAdvances in Ground-Motion Evaluation.Thun J L V eds.American Society of Civil Engineers,Park City,Utah:103--155.
Asten M W,Boore D M.2005.Blind Comparisons of Shear-Wave Velocities at Closely-Spaced Sites in San Jose,Cali-fornia[R].USGS,Open-File Report2005-1169.
Bard P Y,Camplillo M,Chavez-Garcia FJ,Sanchez-Sesma F.1988.The Mexico earthquake of September19,1985:Atheoretical investigation of large-and small-scale amplification effectsin the Mexico City valley[J].Earthquake Spec-tra,4(3):609--633.
Boore D M.2006.Determining near surface shear-wave velocities:Areview[C].Third International Symposiumon theEffects of Surface Geology on Seismic Motion Grenoble,France:103.
Brocher T M.2008.Compressional and shear-wave velocity versus depthrelations for common rocktypesin northern cal-ifornia[J].Bull Seism Soc Amer,98(2):950--968.
Chong J J,Ni S D.2009.Near surface velocity and Qs structure of the Quaternary sediment in Bohai basin,China[J].Earthquake Science,22(5):451--458.
Langston C A.2003.Local earthquake wave propagation through Mississippi embayment sediments,part I:Body-wavephases and local site responses[J].Bull Seism Soc Amer,93(6):2664--2684.
Ni S D,Siddharthan R V,Anderson J G.1997.Characteristics of nonlinear response of deep saturated soil deposits[J].Bull Seism Soc Amer,87(2):342--355.
陈棋福,刘澜波,王伟君,Eric Rohrbach.2008.利用地脉动探测北京城区的地震动场地响应[J].科学通报,53(18):2229--2235.
高玉峰,张健.2007.地震危险性分析研究[M].北京:科学出版社:86--89.
齐诚,赵大鹏,陈颙,陈棋福,王宝善.2006.首都圈地区地壳P波和S波三维速度结构及其与大地震的关系[J].地球物理学报,49(3):805--815.
沈伟森,罗艳,倪四道,崇加军,陈顒.2010.天然地震频率范围内首都圈地区近地表S波速度结构[J].地震学报,32(2):137--146.
于湘伟,陈运泰,王培德.2003.京津唐地区中上地壳三维P波速度结构[J].地震学报,25(1):1--14.
朱露培,曾融生,刘福田.1990.京津唐张地区地壳上地幔三维P波速度结构[J].地球物理学报,33(3):267--277.
Aki K.1988.Local site effects on strong ground motion[G]∥Earthquake Engineering and Soil DynamicsⅡ:RecentAdvances in Ground-Motion Evaluation.Thun J L V eds.American Society of Civil Engineers,Park City,Utah:103--155.
Asten M W,Boore D M.2005.Blind Comparisons of Shear-Wave Velocities at Closely-Spaced Sites in San Jose,Cali-fornia[R].USGS,Open-File Report2005-1169.
Bard P Y,Camplillo M,Chavez-Garcia FJ,Sanchez-Sesma F.1988.The Mexico earthquake of September19,1985:Atheoretical investigation of large-and small-scale amplification effectsin the Mexico City valley[J].Earthquake Spec-tra,4(3):609--633.
Boore D M.2006.Determining near surface shear-wave velocities:Areview[C].Third International Symposiumon theEffects of Surface Geology on Seismic Motion Grenoble,France:103.
Brocher T M.2008.Compressional and shear-wave velocity versus depthrelations for common rocktypesin northern cal-ifornia[J].Bull Seism Soc Amer,98(2):950--968.
Chong J J,Ni S D.2009.Near surface velocity and Qs structure of the Quaternary sediment in Bohai basin,China[J].Earthquake Science,22(5):451--458.
Langston C A.2003.Local earthquake wave propagation through Mississippi embayment sediments,part I:Body-wavephases and local site responses[J].Bull Seism Soc Amer,93(6):2664--2684.
Ni S D,Siddharthan R V,Anderson J G.1997.Characteristics of nonlinear response of deep saturated soil deposits[J].Bull Seism Soc Amer,87(2):342--355.
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