A hybrid numerical technique, combining the finite element and boundary element methods, for modeling elastodynamic scattering problems

Motivated by the demands on earthquake engineering and engineering seismology, a hybrid numerical technique which combines the Boundary Element Method (BEM) with the Finite Element Method (FEM) and its computer algorithms are developed in this thesis for studying the three-dimensional scattering of plane body waves and far-field seismic waves by inhomogeneous cylindrical scatterers with infinite length embedded in an elastic (or layered) half-space.; In this technique, the finite element method is used to model the scatterer to deal with inhomogeneities of the region, and the boundary element method is used to model the semi-infinite half-space to analytically account for the radiation condition. Continuity of displacement and traction forces are enforced on the interface of the two regions. In the final descritized governing equation, the terms contributed by the boundary integral equations for the elastic half-space are considered as an impedance matrix of a "macro finite element". Therefore the frontal solution method can be applied to solve the equation, which greatly saves the computer memory in dealing with large-scale scatterers.; The incoming waves in this study can be plane body waves impinging at an oblique angle with respect to the axis of the inclusion, or seismic waves generated by far-field dislocation faults. In deriving the expression of the seismic wave field in layered half-space due to point dislocations, an efficient numerical method for calculating the ground responses of the layered half-space over an extended region and its computer program are developed.; In an attempt to apply the hybrid numerical technique to the estimation of ground motion, the simulation of the response of the Marina District Basin to the 1989 Loma Prieta earthquake and the response of the Los Angeles Basin to the 1994 Northridge earthquake are conducted. Plane body wave (SH wave) is used to simulate the incoming wave field of the Loma Prieta earthquake, while far-field asymptotic expression of the wave field in the layered half-space due to point dislocation sources are used to model the incoming wave field of the Northridge earthquake.; Using the program developed for calculating the ground response of layered viscoelastic half-space over an extended area due to point dislocations, the ground motion of the Northridge region due to 1994 Northridge earthquake are simulated. The results include the distribution of the ground motions (displacements, velocities, accelerations and strains) and snapshots of the seismic wave propagation over the region.