中文摘要：

基于擂鼓附近地表破裂几何形态的特殊性以及对擂鼓地区地震地表破裂机制存在的不同认识,本文通过野外实际调查测量,并结合已有的文献资料对擂鼓地区地震地表变形特征进行了详细研究。分析结果认为：擂鼓附近几何形态的变化、同震位移量的明显偏小,以及破裂带拐弯处的表层物质发散运动,表明该地区具有一般挤压阶区的特征。由于北川—映秀断裂北段是兼有逆冲运动和右旋走滑运动的断裂,所以相比于一般挤压阶区,擂鼓挤压阶区受到了更强烈的挤压隆升,并且仍受到逆冲引起的撕裂断层作用。擂鼓阶区内形成的滑坡、地表破裂以及鼓包都是局部块体受到强烈挤压作用的结果,而撕裂断层作用影响较小,且完全被挤压隆升变形所掩盖。根据文中的研究并结合已有的深部运动资料,笔者构建了擂鼓挤压阶区三维结构模型。对擂鼓地区的同震变形机制研究不仅有利于我们深入地理解汶川地震的地表破裂过程,也可为断裂阶区内的防震减灾提供理论依据。

英文摘要：

The special characteristics of the rupture induced by 5.12 Wenchuan earthquake in Leigu area is discussed based on the field materials and reported surveying data in this paper because of its unique geometric features and different mechanisms presented by different researchers.Investigation results suggested that the obviously smaller co-seismic deformation and the moving characters of the superficial matter in Leigu area match the general features of restraining step-over.But the north segment of Beichuan-Yingxiu Fault＇s thrust offset is almost equal to its dextral offset,so Leigu restraining step-over（LRS） received more compression than other step-over in the pure strike-slip fault,and the rupture,landslide and pressure ridges were mainly induced by the strong compressional action.Furthermore,the step-over was under the action of the tear fault induced by thrust,but the impact was so small that it was covered by the extruded deformation totally.Combining our research with the materials of deep moving by other geophysical researches,a 3D structural model was introduced to explain the role of Leigu restraining step-over during the forming process of rupture.Our research is not only in favor of the understanding of the process of the Wenchuan earthquake,but also provides the theoretical basis for earthquake disaster prevention in step-over.