汶川Ms8.0地震四川及邻区数字强震台网记录

STRONG MOTION RECORDS OF WENCHUAN Ms8.0 EARTHQUAKE FROM DIGITAL STRONG EARTHQUAKE NETWORKS IN SICHUAN AND ITS NEIGHBOURING REGIONS

2008年5月12日汶川Ms8.0特大地震是龙门山构造带逆冲–右旋错动的结果,四川数字强震台网共获取133组三分向加速度记录,结合陕西、甘肃部分台站观测结果,根据原始记录绘制的加速度峰值等值线呈长轴为NE方向的不规则椭圆形,与地震影响烈度分布具有较好的一致性。进一步分析发现,该次地震的加速度记录具有比较明显的方向性效应和断层上盘效应,即沿破裂传播的NE方向加速度峰值衰减显著慢于SW方向;而处于断层NW上盘的地震动峰值衰减明显慢于SE下盘,出现系统性偏高现象,且在发震断裂的映秀—北川段更为显著,与震源破裂的方式和过程具相关性。另一个现象是近发震断裂的竖向(UD)与水平向(H)地震动峰值的比值明显高于远场,在近断层附近比值在1.0左右,与现行的《建筑抗震设计规范》(GB50011–2001)规定的比值2/3存在较大差异。随断层距的增加,加速度反应谱峰值逐渐移向长周期,当断层距大于200km时更为显著,但在近断层100km时存在速度大脉冲现象。

The thrust-dextral slip motion of Longmenshan tectonic belt resulted in Wenchuan Ms8.0 earthquake occurred on May 12,2008.133 groups of three-component acceleration records were collected by digital strong earthquake networks in Sichuan Province.By using these original records and some strong motion records from digital strong earthquake networks in Shaanxi and Gansu provinces,the contour lines of acceleration peak values were drawn;and they show that the anomalistic ellipse-shaped contour lines of acceleration peak values along the long axis in NE direction conform to the distribution of earthquake response intensity.The attenuation of the acceleration records shows obvious directivity effect and hanging wall effect;i.e.the peak acceleration decayed relatively slower in NE direction of the rupture propagation than in SW direction.The attenuation of peak acceleration also decayed slower on the fault hanging wall in NW direction than that in SE direction;the systemic relative higher phenomenon of the peak acceleration attenuation was more remarkable in Yingxiu—Beichuan section of the causative fault;and it can be relative to fracture pattern and progress of seismic source.Anotherphenomenon is that the ratio of vertical peak ground value to horizontal one near the causative fault is obviously higher than that in the seismic far-field;and the ratio is about 1.0 near the faults,which is great different with the 2/3 from Code for seismic design of buildings（GB50011-2001）.Furthermore,with fault distance increasing,the peak acceleration gradually shifted to the long-period in the acceleration response spectrum,which is more obvious beyond a distance of 200 km to the causative faults;but in the near-fault distance of 100 km,there is a large velocity pulse.