Abstract:

 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.

Key words: Wenchuan earthquake, Longmen Mountains fault zone, Leigu, compressional stepover, tear fault