larger values of $\epsilon_{A}$ exhibit faster velocities. Accordingly, we conclude that the velocity is a monotonically increasing function of $\shearstrain$ and $\pressurestrain$. This is in agreement with the observation of @ziv2019b who generated trains of solitary waves, and found that the taller waves in the train propagate faster than shorter waves. This dependency is the opposite of the dependency of the vector solitary waves observed in the mechanical system conceived by @deng2017, as the two problems are fundamentally different. Notably, our system is a continuum solid which is constitutively and geometrically nonlinear, while the system of @deng2017 is captured by a model of linear springs and rigid squares. Moreover, the physical properties of our continuum are heterogeneous, as its initial mass density varies in space, while in the system of @deng2017 all the springs and squares share the same properties.

We show next that it is possible to bound from below the velocities $c_{+}$ and $c_{-}$ using the velocities in the linear limit (Bloch-Floquet waves) at the low-frequency, long-wavelength regime. Before we proceed, we note that @yong2003solitary have numerically found that the velocity of Bloch-Floquet compression waves in that regime is a lower bound for the velocity of one-dimensional compression 