Abstract
In this paper, unconsolidated siltstone is tested with static and cyclic loading that represents the dynamic force during an earthquake, under K0 and isotropic conditions. Meanwhile, anisotropy of magnetic susceptibility (AMS) is conducted to check the changes in the internal textures of the specimen after these tests. As the results, no major fabric variation within the siltstone was confirmed based on AMS, in spite of substantial residual deformation occurred due to cyclic loading in all test cases. Furthermore, a phenomenon similar to fatigue fracture of metal was observed when the siltstone subjected to cyclic loading under K0 condition. These results are exactly the same as the mechanical properties of décollement zone in which the internal texture remained unchanged but the density increased significantly. In other words, cyclic loading, such as the effective-pressure fluctuation, may become a possible reason for the formation of décollement zone.
