  We analyse the dispersion properties of two types of explicit finite element
methods for modelling acoustic and elastic wave propagation on tetrahedral
meshes, namely mass-lumped finite element methods and symmetric interior
penalty discontinuous Galerkin methods, both combined with a suitable
Lax--Wendroff time integration scheme. The dispersion properties are obtained
semi-analytically using standard Fourier analysis. Based on the dispersion
analysis, we give an indication of which method is the most efficient for a
given accuracy, how many elements per wavelength are required for a given
accuracy, and how sensitive the accuracy of the method is to poorly shaped
elements.
