  We examine the sensitivity of the Love and the quasi-Rayleigh waves to model
parameters. Both waves are guided waves that propagate in the same model of an
elastic layer above an elastic halfspace. We study their dispersion curves
without any simplifying assumptions, beyond the standard approach of elasticity
theory in isotropic media. We examine the sensitivity of both waves to
elasticity parameters, frequency and layer thickness, for varying frequency and
different modes. In the case of Love waves, we derive and plot the absolute
value of a dimensionless sensitivity coefficient in terms of partial
derivatives, and perform an analysis to find the optimum frequency for
determining the layer thickness. For a coherency of the background information,
we briefly review the Love-wave dispersion relation and provide details of the
less common derivation of the quasi-Rayleigh relation in an appendix. We
compare that derivation to past results in the literature, finding certain
discrepancies among them.
