Numerical and Physical Experiments on Dynamic Properties of Elastic Body Waves at the Boundary With Non-rigid Contact Between Media

Abstract

Dynamic interpretation of seismic waves is traditionally based on the model of geological medium as a combination of layers and blocks bounded rigidly to each other. However, a discrepancy has been found between the accumulated theoretical data and experimental data in seismic wave dynamics. Geophysical and rheological study of the Earth¡¦s crustal structure has indicated an important role of layering and fracturing. So, some boundaries in the Earth¡¦s crust can be treated as a non-rigid contact between media, i.e., as a mechanically weakened contact or with thin intermediary layer filled with loose or viscous materials. The theory of non-rigid contact between media has been developed in the literature, but the study of the dynamic characteristics of waves generated at a boundary with non-rigid contact is still required. Here we present the results of numerical and physical ultrasonic experiments on the reflected and transmitted seismic body wave dynamics for the model of non-rigid contact at the boundary between isotropic elastic media. These calculations are based on the non-rigid contact theory which is defined by the boundary conditions with discontinuities of the tangent and normal components of time derivative of the displacement vector across the interface. Our results demonstrate that the amplitude and phase behavior of the generated waves at the non-rigid contact is considerably different from those at the rigid contact between media. The physical ultrasonic experiment was performed for a model of a single fracture on a sheet of duraluminium with a thin filled-plasticine layer. The comparison of physical experimental data with theoretical computations shows a high level of agreement.

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