利用强震数据获取汶川地震近断层地面永久位移

摘要

Records from 64 strong motion stations nearly along the Yingxiu-Beichuan fault in Wenchuan earthquake are used as database.Near fault permanent displacement were derived from acceleration records based on baseline correction,and were compared with GPS observation to investigate the ground motion displacement characteristics induced by Wenchuan Ms8.0 earthquake.The following conclusions can be made from our study:① The ground motion are significant as close to the Yingxiu-Beichuan fault both on the hanging wall and footwall.The permanent displacement from the 51SFB,51MZQ and 51JYH record on the footwall is westward,with a largest displacement of 1.49 m from the 51SFB record,while the 51WCW record on the hanging wall is eastward with a displacement of 1.26 m.② Distribution of permanent displacement shows that the movements of both hanging wall and footwall display a dominant direction toward the Yingxiu-Beichuan fault in the Longmen Shan zone,with east-west displacement being larger than north-south one.The fault mechanism is characterized mainly by a thrust motion,and the thrust motion component is much larger than the strike slip,being consistent with the results of seismic source inversion and field investigation.③ The largest permanent displacements are limited in the narrow rupture zone along the Longmen Shan fault,and reduce rapidly away from the causative fault.It is noted that the permanent displacement in Sichuan basin on the footwall attenuates more rapidly with distance than that on the hanging wall.%利用汶川地震中得到的靠近映秀-北川主断裂的64个强震台站的三分量记录数据,对加速度记录进行基线校正的基础上获取近断层地面运动的永久形变位移,并将由强震记录获取到的地面位移结果与GPS观测到的同震位移进行对比分析,研究汶川Ms8.0地震的近断层地面运动的位移特征.结果表明:①在靠近映秀-北川主断层的上盘和下盘,东西相向的地面运动非常剧烈.下盘的51SFB,51MZQ和51JYH台东西向位移均为负(即地面运动向西),其中51SFB台位移量最大,达到1.49m;上盘的51WCW台位移向东,位移量为1.26 m.②地面运动的位移分布主要表现为以龙门山断裂带的映秀-北川断裂为核心的相向运动,东西方向上的永久位移要大于南北方向.从断层机制上来讲,断层的错动以逆冲运动为主(即逆冲位移要大于走滑分量的位移),这与震源机制反演及地质考察的结果一致.③大的地面永久位移集中分布在以龙门山断裂带为中心的狭长范围内,离开发震断裂地面位移的衰减很快.相比而言,在发震断层的下盘一侧(即四川盆地)的地面位移的衰减比上盘一侧明显要快.