Abstract: In this paper,the rupture propagation along reverse fault in bedrock towards the overlying sediment layer has been studied using modeling tests and the evolution of the vertical displacement field on the surface of sediment layer has been measured using fringe projection technique,in which the effects of fault displacement,thickness of sediment layer and fault dip have been analyzed.The research results indicate that fault in bedrocks propagates gradually towards the overlying sediment layer and a gradient zone of vertical displacement(i.e.a deformation zone)surrounding the projection line of the upper end of fault in bedrock is formed on the surface of sediment layer as the fault slips,given a constant thickness of sediment layer and a constant fault dip.The larger the fault displacement is,the larger the width of the deformation zone and the deformation intensity are.However,the width of deformation zone keeps constant and only the deformation becomes more concentrated as fault displacement increases after the fault propagates to the surface of sediment layer.Under the same fault displacement and the same fault dip,the thicker the sediment layer is,the wider the deformation zone controlled by the fault in bedrock is,i.e.the larger the influencing extent of the fault is.When the thickness of sediment layer exceeds a critical thickness,an extensional rupture may occur on the surface of the sediment layer caused by uplifting of the sediment layer.Under the same thickness of sediment layer and the same fault displacement,the width of the deformation zone on the surface of sediment layer decreases but the deformation intensity increases as fault dip increases.The experiment results imply that the critical fault displacement,the critical thickness of sediment layer and the fault dip play important roles in determining the surface deformation and rupture of earthquake generated by buried reverse fault.The results obtained in this paper are valuable for further understanding the characteristics of surface deformation caused by Wenchuan earthquake.

Key words: buried reverse fault, modeling test, fringe projection technique, rupture propagation

摘要： 通过模拟实验研究了逆断层活动过程中上覆沉积层的破裂扩展特征,采用投影条纹测试方法分析了沉积层表面离面(即垂直)位移场的演化过程。结果表明,在沉积层厚度和断层倾角一定的条件下,基岩中的逆断层逐渐向上扩展,并在沉积层表面围绕基岩断层上断点的投影线形成一个离面位移梯度带(即形变带),基岩断层的位移越大,沉积层中的形变带越宽、变形越强烈;但当断层扩展至沉积层表面后,形变带宽度将保持稳定,只是变形随断层位移增加而更集中。对于同样的基岩断层位移和断层倾角,沉积层厚度越大,受基岩断层控制的形变带越宽,即基岩断层的影响范围越大;当沉积层厚度超过某一临界值时,沉积层中会发育因隆起引起的表面拉张破裂。在沉积层厚度和基岩断层位移量一定的情况下,基岩断层倾角的增加将会使表面形变带的宽度减小,但会使变形破坏程度更强烈。实验结果意味着,临界断层位移、临界沉积层厚度以及断层倾角对于确定隐伏逆断层发震产生的地表变形和破坏特征具有重要意义。文中的研究结果有助于进一步认识汶川M_S 8.0地震的地表变形特征。

关键词: 隐伏逆断层, 模拟实验, 投影条纹测试方法, 破裂扩展