基于小波方法的近断层地震动速度脉冲周期的统计特性
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摘要
采用小波方法筛选出了180条断层距在20 km之内且PGV大于10 cm/s的具有速度脉冲特征的近断层地震波,分别对基岩和土层场地、走滑(SS)和非走滑(NSS)断层、不同脉冲峰值标准情形下近断层脉冲周期和矩震级的关系进行了统计,得到了不同情形下脉冲周期-震级经验公式回归系数,以供近场地震动速度脉冲的相关研究参考使用。结果表明:走滑断层产生的脉冲周期比非走滑断层的大,但随震级的增大情况发生变化;无论走滑断层还是非走滑断层,当震级较小时,土层场地的脉冲周期比基岩场地的大,随着震级的增加,基岩场地的脉冲周期将比土层场地的大;根据不同标准的速度脉冲峰值PGV记录,得到的周期-震级关系曲线有很大区别。
In this paper, 180 records are selected based on wavelet approach. These records show three common features: their rupture distances are less than 20 km, their peak ground velocity(PGV) are greater than10cm/sec and they all show characteristics of velocity pulses for near-fault strong motions. All Records are divided into groups according to different site conditions(rock vs. soil), different fault types(strike-slip fault vs. non-strike-slip fault) and different PGV threshold levels. Regression coefficients of several period-magnitude relationships in different situations are then given. With statistics in hand, several conclusions can bemade: 1 pulse periods in strike-slip faults are greater than those in non-strike-slip faults, but things changed with moment magnitude greater than 7, which is believed to have relationship with insufficient severe earthquake records. With limited severe earthquake records, the result may be affected. 2 In both strike-slip faults' and non-strike-slip faults' cases, pulse periods in rock sites are greater than those in soil sites with moment magnitude less than 6.5 or so, and pulse periods in rock sites will be greater than those in soil sites as moment magnitude increases, but the boundary line on which pulse periods change differs according to different fault types. 3 The period-magnitude relationships derived from different PGV threshold levels varies a lot. For nonstrike-slip faults, both soil sites and rock sites show the same property, that is, when magnitude is relatively small, the higher the PGV threshold level is, the smaller the pulse periods will be, however, pulse periods increase with the moment magnitude, when the moment magnitude reaches a certain degree, pulse periods from lower PGV threshold levels will be greater than those from higher ones. However, for non-strike-slip faults, in soil sites' cases, it is just the other way around, while in rock sites' cases, such trend is not obvious, which may be caused by limited data volume.
In this paper, 180 records are selected based on wavelet approach. These records show three common features: their rupture distances are less than 20 km, their peak ground velocity(PGV) are greater than10cm/sec and they all show characteristics of velocity pulses for near-fault strong motions. All Records are divided into groups according to different site conditions(rock vs. soil), different fault types(strike-slip fault vs. non-strike-slip fault) and different PGV threshold levels. Regression coefficients of several period-magnitude relationships in different situations are then given. With statistics in hand, several conclusions can bemade: 1 pulse periods in strike-slip faults are greater than those in non-strike-slip faults, but things changed with moment magnitude greater than 7, which is believed to have relationship with insufficient severe earthquake records. With limited severe earthquake records, the result may be affected. 2 In both strike-slip faults' and non-strike-slip faults' cases, pulse periods in rock sites are greater than those in soil sites with moment magnitude less than 6.5 or so, and pulse periods in rock sites will be greater than those in soil sites as moment magnitude increases, but the boundary line on which pulse periods change differs according to different fault types. 3 The period-magnitude relationships derived from different PGV threshold levels varies a lot. For nonstrike-slip faults, both soil sites and rock sites show the same property, that is, when magnitude is relatively small, the higher the PGV threshold level is, the smaller the pulse periods will be, however, pulse periods increase with the moment magnitude, when the moment magnitude reaches a certain degree, pulse periods from lower PGV threshold levels will be greater than those from higher ones. However, for non-strike-slip faults, in soil sites' cases, it is just the other way around, while in rock sites' cases, such trend is not obvious, which may be caused by limited data volume.
引文
[1]刘启方,袁一凡,金星,等.近断层地震动的基本特征[J].地震工程与工程振动,2006,26(1):1-10.
[2]姜慧,黄剑涛,俞言祥,等.地表破裂断层近场速度大脉冲研究[J].华南地震,2009,29(02):1-9.
[3]Alavi B,Krawinkler H.Consideration of near-fault motion effects in seismic design[C]//New Zealand:12WCEE,2000.
[4]Somerville,P.G.Magnitude scaling of the near fault rupture directivity pulse[J].Physics of the earth and planetary interiors,2003,137(1):201-212.
[5]Mavroeidis,G.P.,and A.S.Papageorgiou.A mathematical representation of near-fault ground motions[J].Bulletin of the Seismological Society of America,2003,93(3):1099-1131.
[6]Bray J D.,Rodriguez-Marek A.Characterization of forward-directivity ground motions in the near-fault region[J].Soil Dyn Earthquake,2004,24(11):815-828.
[7]刘启方,金星,袁一凡.均匀弹性全空间中走滑断层产生的方向性速度脉冲研究[J].地震工程与工程振动,2007(02):12-19.
[8]韦韬,赵凤新,张郁山.近断层速度脉冲的地震动特性研究[J].地震学报,2006,28(6):629-637.
[9]谢俊举,温增平,李小军,等.基于小波方法分析汶川地震近断层地震动的速度脉冲特性[J].地球物理学报,2012,55(6):1963-1972.
[10]Somerville,P.G.,Smith,N.F.,Graves,R.W.,et al.Modification of empirical strong ground motion attenuation relations to include the amplitude and duration effects of rupture directivity[J].Seismological Research Letters,1997,68(1):199-222.
[11]J W Baker.Quantitative classification of near-fault ground motions using wavelet analysis[J].Bulletin of the Seismological Society of America,2007,97(5):1486-1501.
[12]中国国家标准化管理委员会.GB/T 17742-2008中国地震烈度表[S].北京:中国标准出版社,2008.
[13]International Code Council.INCIBC2009 International Building Code[S].USA:Printed unknoun,2009.
[14]Rodriguez M A,Bray J D,Abrahamson N A.A geotechnical seismic site response evaluation procedure[C]//New Zealand:12WCEE,2000.
[2]姜慧,黄剑涛,俞言祥,等.地表破裂断层近场速度大脉冲研究[J].华南地震,2009,29(02):1-9.
[3]Alavi B,Krawinkler H.Consideration of near-fault motion effects in seismic design[C]//New Zealand:12WCEE,2000.
[4]Somerville,P.G.Magnitude scaling of the near fault rupture directivity pulse[J].Physics of the earth and planetary interiors,2003,137(1):201-212.
[5]Mavroeidis,G.P.,and A.S.Papageorgiou.A mathematical representation of near-fault ground motions[J].Bulletin of the Seismological Society of America,2003,93(3):1099-1131.
[6]Bray J D.,Rodriguez-Marek A.Characterization of forward-directivity ground motions in the near-fault region[J].Soil Dyn Earthquake,2004,24(11):815-828.
[7]刘启方,金星,袁一凡.均匀弹性全空间中走滑断层产生的方向性速度脉冲研究[J].地震工程与工程振动,2007(02):12-19.
[8]韦韬,赵凤新,张郁山.近断层速度脉冲的地震动特性研究[J].地震学报,2006,28(6):629-637.
[9]谢俊举,温增平,李小军,等.基于小波方法分析汶川地震近断层地震动的速度脉冲特性[J].地球物理学报,2012,55(6):1963-1972.
[10]Somerville,P.G.,Smith,N.F.,Graves,R.W.,et al.Modification of empirical strong ground motion attenuation relations to include the amplitude and duration effects of rupture directivity[J].Seismological Research Letters,1997,68(1):199-222.
[11]J W Baker.Quantitative classification of near-fault ground motions using wavelet analysis[J].Bulletin of the Seismological Society of America,2007,97(5):1486-1501.
[12]中国国家标准化管理委员会.GB/T 17742-2008中国地震烈度表[S].北京:中国标准出版社,2008.
[13]International Code Council.INCIBC2009 International Building Code[S].USA:Printed unknoun,2009.
[14]Rodriguez M A,Bray J D,Abrahamson N A.A geotechnical seismic site response evaluation procedure[C]//New Zealand:12WCEE,2000.
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