【摘要】 选取断层距小于200km的64组强震记录数据,基于小波方法分析汶川地震近断层速度脉冲的地震动特性,并将此次地震中获取到的速度脉冲周期和幅值参数与Chi-Chi地震和Northridge地震进行了比较,统计分析地震震级、距离对速度脉冲的周期和幅值参数的影响.研究表明:(1)汶川地震近断层速度脉冲具有周期长、幅值小的特点.速度脉冲周期主要分布在6～14s之间,其中51MZQ台沿平行断层的分量脉冲周期最大为14.2s,速度脉冲幅值与Chi-Chi地震和Northridge地震相比明显偏小.(2)速度脉冲记录出现在沿着地震断层破裂传播的方向上,且与地表断裂的距离都在30km以内,这些长周期速度脉冲的形成可能主要由破裂传播的向前方向性效应引起.(3)速度脉冲的周期随矩震级呈对数线性增大,且随断层距增大有减小趋势.在矩震级小于Mw7.5时,观测到的地震动脉冲幅值为50～150cm/s之间,与100cm/s的典型断层滑动速率非常接近;而震级大于Mw7.5时,断层距10km范围内脉冲的幅值已经超过100cm/s,个别记录的脉冲幅值甚至达到200cm/s,远超过前人给出的饱和值,这可能与大的永久形变或该处土层介质条件有关.更多还原

【Abstract】 Characteristics of near-fault velocity pulses during the Wenchuan earthquake are analyzed based on wavelet analysis methods.64 groups of strong motion records within 200 km to the causative fault are used as database.The amplitude and period characteristics of velocity pulses from Wenchuan earthquake are compared with the Chi-Chi and Northridge earthquake,and the relationships of pulse amplitude and period with magnitude and fault distance are also analyzed.Based on the analysis of near-fault ground motion containing velocity pulses,the following conclusions can be made:(1) The near-fault velocity pulses from Wenchuan earthquake are characterized as long period and low amplitude.The pulse periods are about 6~14 s,with the largest pulse period reaching 14.2 s which is recorded by fault parallel component of the 51MZQ station,and the pulse amplitudes are relatively small for the Wenchuan earthquake compared with the Chi-Chi and Northridge earthquake.(2) Large velocity pulses are observed at sites where the rupture propagated toward the recording station and close to rupture projection with fault distance smaller than 30 km.It can be concluded that the recorded long period pulses are mainly caused by forward directivity effects.(3) The pulse periods are logarithmicly linear increasing with the moment magnitude,and the periods have a trend of decreasing with fault distance.The recorded pulse amplitudes vary from 50~150 cm/s for records with moment magnitude smaller than 7.5,which is very close to the typical slip velocity 100 cm/s;while for records with magnitude larger than 7.5,the pulse amplitudes can easily exceed 100 cm/s,and can reach 200 cm/s for some records,which might be correlated with the larger fling-step and site condition in local area.更多还原