断层错动引发基岩上覆土层破裂过程模拟

 利用有限元方法对断层基岩错动引发上覆土层破裂过程进行数值模拟，展示场地土层破裂形成和扩展特征，以及场地地表出现破裂并不一定形成土层贯通破裂的地震现象。研究表明，土层破裂始于土层与基岩的交界面并向上扩展，而随着断层基岩错动量的增加，场地地表出现破裂(单个或两个)并向下扩展，在断层基岩错动量达到一定值时上下扩展的破裂在土层某一深度位置相连形成土层贯通破裂；不同的断层基岩错动量和覆盖土层条件将导致隐覆破裂、非贯通地表破裂和贯通破裂3类不同的场地地震破裂现象。研究进一步揭示土层厚度和特性对土层破裂特征的影响。当出现地表破裂时，土层越厚破裂带的宽度越大，砂土形成的破裂带宽度小于黏土；土层越硬，越易于形成贯通破裂；土层厚度和土质特性对土层破裂的破裂角影响不明显；对于逆冲断层，地表土层初始破裂出现所需的基岩位错量约为贯通破裂位错量的80%或更小，50 m以内的覆盖土层产生贯通破裂的基岩位错垂直量小于上覆土层厚度的5%。

SIMULATION OF FAULT MOVEMENT INDUCED RUPTURE PROCESS OF OVERLAYING SOIL OF BEDROCK

Earthquake fault dislocation-induced ruptures of soil layers are simulated by finite element method. The study demonstrates soil rupture propagation and characteristics，and also proves the observed earthquake phenomenon that a ground surface rupture failure does not mean a penetrating rupture failure. The simulation results indicate that the soil rupture starts at interface between soil and bedrock and expands upward. Furthermore，one or two ruptures appear at ground surface and extend downward with the increase of fault dislocation，and the ruptures from bedrock and ground surface meet somewhere in soils so that a penetrating rupture from bedrock to ground surface occurs if fault dislocation is large enough. Three kinds of soil ruptures including buried rupture，non-penetrating ground surface rupture and penetrating soil rupture are presented in case of different fault dislocations and soil conditions. The obvious effects of soil thickness and properties on characteristics of soil rupture are revealed. The ground surface rupture belt is enlarged due to the increase of soil thickness if a ground surface rupture occurs，and the rupture angle is almost not affected by soil thickness and properties. The width of rupture belt of sands is smaller than that of clays，and the penetrating rupture occurs more easily for harder soil than for softer soils. In condition of reverse fault，the value of bedrock fault dislocation for initial ground surface rupture occurring is 80% or less than that for a penetrating rupture occurring，and the vertical value of bedrock fault dislocation for a penetrating rupture occurring is 5%less than that of soil thickness for soil layer with thickness less than 50 m.