Simulating the earthquake response of a large basin is accomplished by solving numerically the partial differential equations of elastic wave propagation, i.e., Navier's equations of elastodynamics. A variety of numerical methods have been used for approximating the solution of these problems. In practice, the seismic response of three-dimensional elastic features has been modeled by different methods, e.g., multipolar expansions of wave functions [39], ray theory [27], the Aki-Larner method [21], the finite-element method [45, 28, 38], the finite-difference method [33, 32, 17, 16, 50], the boundary-element method [29, 35], hybrid techniques [23], and asymptotic methods [37]. The most realistic numerical simulations to date are those obtained by finite-differences methods, boundary-element methods, and finite element methods.