Abstract: The epicenter intensity of the M_S 8.0 Wenchuan earthquake of 12^th May 2008 is Ⅺ.Hanwang town,Mianzhu county,Sichuan Province,located on the edge of seismic intensity Ⅹ zone,suffered the seismic intensity one degree higher than the surroundings,in the respects of both the houses damaged or the number of victims and missing persons,as close to the destruction in meizoseismal region.In this paper,the distribution pattern of the earthquake surface rupture zone around Hanwang town is discussed,focusing on the causes for the aggravation of seismic damage.The paper introduces two left-step en echelon surface rupture zones,which are 1.5km apart,located at the north and south of Hanwang town.The one on the north of Hanwang town has a vertical displacement of 1.4m and horizontal dextral displacement 0.44m,respectively.The other on the south of Hanwang town has a vertical displacement of 3.0～0.2m,descending from west to east.Although the two surface rupture zones did not pass through the center of the town,since Hanwang town is located right in the sinistral stepover clamped by the two surface rupture zones,the buildings in the stepover were subject not only to the vibration from the seismic source but also the compression inside the stepover,thus aggravating the damage of the buildings in Hanwang town.This also shows the diversity of building damage by the surface rupture zone.The seismic damage of Wenchuan earthquake around Hanwang town shows that the stepover of the surface rupture zone is also the special structural part subject to aggravated damage in earthquake.

Key words: Wenchuan M_S8.0 earthquake, surface rupture zone, en echelon stepover, significance of seismic damage, Hanwang town

摘要： 2008年5月12日汶川M_S8.0地震的震中烈度为Ⅺ度,但位于地震烈度为Ⅹ度区边缘的绵竹县汉旺镇,无论是房屋毁坏情况还是遇难和失踪人员的数目,均高出周边地震烈度Ⅰ度,接近极震区的破坏程度。文中从汉旺镇周边地表地震破裂带展布方式的角度讨论了这种震害加重现象的原因,介绍了位于汉旺镇北面和南面出现的2条相距1.5km呈左阶斜列展布的地表破裂带。其中,位于汉旺镇北侧的地表破裂带,垂直位移1.4m,水平右旋位移0.44m;位于汉旺镇南侧的地表破裂带,垂直位移量由西向东递减,为3.0～0.2m。尽管这2条地表破裂带没有从汉旺镇中心通过,但汉旺镇正位于这2条地表破裂带夹持的左阶阶区,致使阶区内建筑物除遭受来自震源的振动外,又受到阶区内的挤压,由此加重了汉旺镇建筑物的破坏,也显示出地表破裂带对建筑物破坏形式的多样性。汉旺镇汶川M_S8.0地震震害实例表明,地表破裂带的阶区,也是遭受地震时破坏加重的特殊构造部位。

关键词: 汶川M_S8.0地震, 地表破裂带, 雁行阶区, 震害意义, 汉旺镇