汶川地震中强震持时的特征研究
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摘要
基于汶川地震断层距150 km内56个台站三分量加速度记录分析地震动重要持时的特征,并建立了持时与断层距的拟合关系。与已建立的持时公式比较,以往分析结果都大大低估了汶川地震动持时。近断层特征对地震动持时有显著影响。断层距小于30 km,上盘和下盘场点的持时明显低于平均水平;断层距大于30 km,地震动持时受到下盘效应的影响,持时较长。破裂方向性效应引起地震动持时在垂直断层方向与水平方向上的差异,同时断层破裂前方向场点的地震动持时较短,比破裂后方向场点的持时小近一倍。
56 stations within 150 km to causative fault surface are used as database to analyze the characteristics of the durations of ground motions during the Wenchuan earthquake.A simple attenuation relation in terms of rupture distance is proposed and compared with some available predictions.Previous equations of duration largely underestimated the durations of ground motions for this earthquake.The near-fault characteristics have impact upon the durations.Within rupture distance 30 km,the durations on hanging wall and footwall are lower than the attenuation relation.For the rupture distance larger than 30 km,the durations are strongly influenced by footwall effect.The differences of durations resulting from directivity effects between fault normal and fault parallel are found.Durations of ground motions close to rupture fault are significantly different between the forward and backward direction,and this difference reaches nearly 2 times on average.
56 stations within 150 km to causative fault surface are used as database to analyze the characteristics of the durations of ground motions during the Wenchuan earthquake.A simple attenuation relation in terms of rupture distance is proposed and compared with some available predictions.Previous equations of duration largely underestimated the durations of ground motions for this earthquake.The near-fault characteristics have impact upon the durations.Within rupture distance 30 km,the durations on hanging wall and footwall are lower than the attenuation relation.For the rupture distance larger than 30 km,the durations are strongly influenced by footwall effect.The differences of durations resulting from directivity effects between fault normal and fault parallel are found.Durations of ground motions close to rupture fault are significantly different between the forward and backward direction,and this difference reaches nearly 2 times on average.
引文
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[18]Wang G Q,Zhou X Y,Zhang P Z,et al.Characteristics of amplitude and duration for near fault strong ground motion from the 1999 Chi-Chi[J].Soil Dynamics and Earthquake Engineering,2002,22(1):73-96.
[2]Bradley B A.Correlation of significant duration with amplitude and cumulative intensity measures and its use in ground motion selection[J].Jour-nal of Earthquake Engineering,2011,15(6):809-832.
[3]Esteva L,Rosenblueth E.Espectros de temblores a distancias moderadas y grandes[J].Bulletin of the Mexican Society of Seismic Engineering,1964,2:1-18.
[4]Novikova E I,Trifunac M D.Duration of strong motion:physical basis and empirical equation[R].Department of Civil Engineering,Universityof Southern California,Los Angeles,1993,93(02).
[5]Eduardo R,Ordaz M.Duration of Strong ground motion during Mexican earthquakes in terms of magnitude,distance to the rupture area and domi-nant site period[J].Earthquake Engineering and Structural Dynamics,2001,30(5):653-673.
[6]Kempton J J,Stewart J P.Prediction equations for significant duration of earthquake ground motions considering site and near-source effects[J].Earthquake Spectra,2006,22(4):985-1013.
[7]Somerville P G,Smith N F,Graves R W,et al.Modification of empirical strong ground motion attenuation relations to include the amplitude andduration effects of rupture directivity[J].Seismological Research Letters,1997,68(1):199-222.
[8]Liu Qifang,Li Xiaojun.Preliminary analysis of the hanging wall effect and velocity pulse of the 5.12 Wenchuan earthquake[J].Earthquake Engi-neering and Engineering Vibration,2009,8(2):165-177.
[9]Wen Zengping,Xie Junju,Gao M.et al.Near-source strong ground motion characteristics of the 2008 Wenchuan earthquake[J].Bulletin of theSeismological Society of America,2008,100(5B):2425-2439.
[10]Wang Dong,Xie Lili,Abrahamson N A,et al.Comparison of strong ground motion from the Wenchuan,China,earthquake of 12 May 2008 withthe Next Generation Attenuation(NGA)ground-motion models[J].Bulletin of the Seismological Society of America,2008,100(5B):2381–2395.
[11]Abrahamson N A,Somerville P G.Effects of the hanging wall and footwall on ground motion recorded during the Northridge earthquake[J].Bul-letin of the Seismological Society of America,1996,86(1B):S93-S99.
[12]GB50011-2001建筑抗震设计规范[S].GB50011-2001 Code for Seismic Design of Buildings[S].
[13]Trifunac M D,Brady A G.A study on the duration of strong ground motion[J].Bulletin of the Seismological Society of America,1975,65(3):581-626.
[14]尹宝江,黄宗明,白绍良.对地震地面运动持续时间定义的对比分析及改进建议[J].工程抗震,1999,2(6):44-46.YIN Baojiang,HUANG Zongming,BAI Shaoliang.Comparison and improvement on the duration of ground motion[J].Journal of EngineeringResistance,1999,2(6):43-46.(in Chinese)
[15]Trifunac M D,Westermo B D.Duration of strong earthquake shaking[J].Soil Dynamics and Earthquake Engineering,1982,1:117-121.
[16]Bommer J J,Stafford P J,Alarcón J E.Empirical equations for the prediction of the significant,bracketed,and uniform duration of earthquakeground motion[J].Bulletin of the Seismological Society of America,2009,99(6):3217-3233.
[17]赵艳,付丽艳,韩卫,等.震中矩对水平向能量持时的影响分析[J].佳木斯大学学报,2008,26(5):630-635.ZHAO Yan,FU Liyan,HAN Wei,et al.The influence of epicenter distance to horizontal earthquake ground motion duration[J].Journal of Jia-musi Universit,2008,26(5):630-635.(in Chinese)
[18]Wang G Q,Zhou X Y,Zhang P Z,et al.Characteristics of amplitude and duration for near fault strong ground motion from the 1999 Chi-Chi[J].Soil Dynamics and Earthquake Engineering,2002,22(1):73-96.
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