首都圈平均波速比分析
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摘要
首都圈数字地震台网覆盖京、津和河北中部,其中自2002年5月—2003年12新记录1级以上地震1186个,台站记录的纵、横波到时差约2~25 s。选取被5个以上台站所记录到的地震,震中位于网内或者网缘附近,计算其平均波速比。分析认为:(1)通过HYPODD修订震源位置,绝大多数震源深度在8~10 km,平均波速比所反映的是地壳上层的状态。(2)无论是从较长的时间尺度还是从较大的空间范围来看,平均波速比值都是非常稳定的。(3)平均波速比的可靠性有赖于较多的台站数目,以满足拟合精度的要求。少数台站的测定结果往往伴随较大的误差,单一地震的平均波速比值大幅度的涨落,不宜表征地壳介质性质的改变。
The Capital Digital Seismic Network,covering Beijing,Tianjin and central Hebei province,has recorded 1186 new earthquakes with M≥1.0 during May 2002 to Dec.2003,in which the arrival time differences between longitudinal wave and transverse wave are 2~25 s.Choosing the earthquakes recorded by 5 or above 5 stations,and demanding the epicenters are located in the network or near its edge,we calculate the average velocity ratios in this area.It is thought on the analysis that:(1) The majority of earthquakes are at depth of 8~10 km,after relocating the focus by HYPODD,so the average velocity ratio we obtained can only reflect the state in the upper crust.(2) The average velocity ratios are very steady,whatever in the long time scale or large spatial scale.(3) The reliability of average velocity ratios relies on the number of stations to satisfy the fitting precision.The results from fewer stations are always accompanied by larger errors,and single earthquake with big amplitude of change in average velocity ratio is not suitable to represent the property change of crustal media.
The Capital Digital Seismic Network,covering Beijing,Tianjin and central Hebei province,has recorded 1186 new earthquakes with M≥1.0 during May 2002 to Dec.2003,in which the arrival time differences between longitudinal wave and transverse wave are 2~25 s.Choosing the earthquakes recorded by 5 or above 5 stations,and demanding the epicenters are located in the network or near its edge,we calculate the average velocity ratios in this area.It is thought on the analysis that:(1) The majority of earthquakes are at depth of 8~10 km,after relocating the focus by HYPODD,so the average velocity ratio we obtained can only reflect the state in the upper crust.(2) The average velocity ratios are very steady,whatever in the long time scale or large spatial scale.(3) The reliability of average velocity ratios relies on the number of stations to satisfy the fitting precision.The results from fewer stations are always accompanied by larger errors,and single earthquake with big amplitude of change in average velocity ratio is not suitable to represent the property change of crustal media.
引文
[1]张成科,张先康,赵金仁,等.渤海湾及其邻区壳幔速度结构研究与综述[J].地震学报,2002,24(4),428-435.
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[4]于湘伟,陈运泰,王培德.京津唐地区中上地壳三维P波速度结构[J].地震学报,2003,25(1),1-14.
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[6]傅征祥,程燕.北京和张家口地区地壳平均波速比的联合测定[J].地震,1988,(4):28-34.
[7]栗生平,傅征祥.华北地区地震带分段波速比平均值的测定[A].见:国家地震局科技发展司,中国大陆2005年前强震危险性预测研究[C].北京:地震出版社,1997.96-99.
[8]Smith E G C.Joint determination of seismic velocity ratios:Theory and application to an aftershock sequence[J].Bull.Seic.Soc.Am.,1983,73(2):405-417.
[9]黎晓明,张晓东.应用多台法测定华北地区地壳的平均波速比[J].地震,2004,24(1),163-169.
[10]Scholz C H.马胜利,等译,地震与断层力学[M].北京:地震出版社,1990.364.
[11]Semenov A N.Variations of the travel time of transverse andlongitudinal waves before violent earthquakes[J].Izv.Acad.Sci.USSR,Phys.Solid Earth(Eng.trans.),1969,(3):245-258.
[12]Aggarwal Y P,Sykes L R,Simpson D W,et al.Spatial andtemporal variations ofts/tpand in P wave residual at blueMountain Lake,New York:Application to earthquake pre-diction[J].J.Geophys.Res.,1973,80:718-732.
[13]McEvilly T V,Johnson L R.Stability of p and s velocitiesfrom central California quarry blasts[J].Bull.Seismol.Soc.Am.,1974,64:343-353.
[14]Mogi K.Earthquake Prediction[M].Tokyo:AcademicPress,1985.
[15]冯德益.地震波速变化[M].北京:地震出版社,1981.
[16]张学民,刁桂苓,束沛镒,等.华北地区地下介质波速比值(Vp/Vs)研究[J].地震地质,2004,26(2),305-317.
[17]张学民,刁桂苓,束沛镒.鄂尔多斯块体及其东南缘剪切波速度结构与波速比研究[J].中国地震,2004,20(1),53-63.
[2]祝治平,张先康,盖玉杰,等.邢台震源区及其邻近地区地壳上地幔速度结构研究[J].地震学报,1992,27(3):328-334.
[3]Jinli Huang,Dapeng Zhao.Crustal heterogeneity and seis-motectonics of the region around Beijing,China[J].Tectono-physics,2004,385:159-180.
[4]于湘伟,陈运泰,王培德.京津唐地区中上地壳三维P波速度结构[J].地震学报,2003,25(1),1-14.
[5]嘉世旭,刘昌铨.邢台震源区波速比异常与地震的关系[J].地震学报,1996,39(增刊),205-215.
[6]傅征祥,程燕.北京和张家口地区地壳平均波速比的联合测定[J].地震,1988,(4):28-34.
[7]栗生平,傅征祥.华北地区地震带分段波速比平均值的测定[A].见:国家地震局科技发展司,中国大陆2005年前强震危险性预测研究[C].北京:地震出版社,1997.96-99.
[8]Smith E G C.Joint determination of seismic velocity ratios:Theory and application to an aftershock sequence[J].Bull.Seic.Soc.Am.,1983,73(2):405-417.
[9]黎晓明,张晓东.应用多台法测定华北地区地壳的平均波速比[J].地震,2004,24(1),163-169.
[10]Scholz C H.马胜利,等译,地震与断层力学[M].北京:地震出版社,1990.364.
[11]Semenov A N.Variations of the travel time of transverse andlongitudinal waves before violent earthquakes[J].Izv.Acad.Sci.USSR,Phys.Solid Earth(Eng.trans.),1969,(3):245-258.
[12]Aggarwal Y P,Sykes L R,Simpson D W,et al.Spatial andtemporal variations ofts/tpand in P wave residual at blueMountain Lake,New York:Application to earthquake pre-diction[J].J.Geophys.Res.,1973,80:718-732.
[13]McEvilly T V,Johnson L R.Stability of p and s velocitiesfrom central California quarry blasts[J].Bull.Seismol.Soc.Am.,1974,64:343-353.
[14]Mogi K.Earthquake Prediction[M].Tokyo:AcademicPress,1985.
[15]冯德益.地震波速变化[M].北京:地震出版社,1981.
[16]张学民,刁桂苓,束沛镒,等.华北地区地下介质波速比值(Vp/Vs)研究[J].地震地质,2004,26(2),305-317.
[17]张学民,刁桂苓,束沛镒.鄂尔多斯块体及其东南缘剪切波速度结构与波速比研究[J].中国地震,2004,20(1),53-63.
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