This article presents the verification of a spectral-element method (SEM) code using the so-called layer over half-space 3 (LOH.3) benchmark model of the Southern California Earthquake Center to 7 Hz with a minimum S-wave velocity of 2000 m/s. First, the approach of Liu and Archuleta (2006) is successfully implemented in an explicit SEM, then, it is shown that the SEM code displays excellent goodness of fits (GOFs) with five Gauss-Lobatto-Legendre (GLL) nodes per wavelength at 7 Hz. A parametric study on the influence of the number of GLL nodes per wavelength shows that more than five GLL nodes per minimum wavelength do not significantly increase the accuracy; however, a decrease of the accuracy starts to be seen from four GLL nodes. A parametric study of the influence of the number of relaxation mechanism on the accuracy of the numerical response shows that, for this specific case, six to eight relaxation mechanisms are sufficient to reproduce the reference solution, whereas below six the viscoelastic response is strongly affected and tends to an elastic response when using two relaxation mechanisms only.