We study dynamical behaviors of a system composed of two elastically coupled blocks on a moving rough plate both analytically and numerically. The system exhibits a rich variety of behaviors including chaos because of the nonlinearity involved in the friction. The behaviors are reminiscent of irregular motions observed in an earthquake fault model composed of many blocks, which suggests that some of the characteristics in the fault model originate in the nonlinearity of a dynamical system with a few degrees of freedom.
We perfomed three-dimensional (3D) visualization of two plate models of the Philippine sea plate, which is descending beneath the Kanto district. Here we present three different representations, using the wire frame, anaglyph and shading methods. Such visualization makes the difference in shape between the plate models easy to understand with the eye. One model has an overall concave surface, while the other is characterized by a somewhat convex surface. Finite element analysis was performed on the two plate models to investigate their elastic behavior when subjected to a compressive force. This force represents the NW-SE compressive stress acting on the Philippine Sea plate beneath the Kanto district. While in appearance the two models are quite different in form, we found that in terms of elastic deformation their behavior was rather similar. Both plate models commonly show clear upheavals near the region where the 1923 Kanto earthquake occurred. This means that when the Philippine sea plate is subject to a NW-SE compressive stress it tends to be in strong contact with the upper continental plate near the focal region of the 1923 Kanto earthquake, due to upward bending of the plate. Inversion analysis of geodetic data has shown that the Philippine Sea plate and the continental plate are strongly coupled in this region during interseismic periods. Our computations suggest the possibility that this strong coupling in interseismic periods may result from mechanical deformation of the subducting plate in a compressive stress field.