Compact second-order time-domain perfectly matched layer formulation for elastic wave propagation in two dimensions

A new second-order formulation is obtained for elastic wave propagation in 2D media bounded by a perfectly matched layer (PML). The formulation uses a complex coordinate stretching approach with a two-parameter stretch function. The final system, consisting of just two second-order displacement equations along with four auxiliary equations, is smaller than existing formulations, thereby simplifying the problem and reducing the computational cost. With the help of a plane-wave analysis, the stability of the continuous formulation is examined. It is shown that by increasing the scaling parameter in the stretch function, any existing instability is moved to higher spatial frequencies. Since discrete models cannot resolve frequencies beyond a certain limit, this can lead to significant computational stability improvements. Numerical results are shown to validate our formulation and to illustrate the improved stability that can be achieved with certain anisotropic media that have known issues.