According to Stephen Eales' Planets & Planetary Systems, pp. 73-75, earthquake longitudinal Compression Waves (P-Waves) travel w/ velocity:

[math]v_{p}^{2} = \frac{\left( K + \frac{4 \; \mu}{3} \right)}{\rho}[/math]

while transverse Shear Waves (S-Waves) travel w/ velocity:

[math]v_{p}^{2} = \frac{\mu}{\rho}[/math]

where "K is the bulk modulus of the rock, [math]\mu[/math] is its shear modulus, and [math]\rho[/math] is its density". His discussions seemingly suggest, that the bulk & shear moduli of rock remain roughly constant, across the range of conditions encountered in planetary interiors.

 

Since earthquake wave velocities are inversely proportion to density, earthquake waves might travel faster, on smaller, lighter, lower-gravity, less-dense worlds, like the Moon & Mars. Conversely, such waves might travel slower on larger, more-massive, higher-gravity, higher-density worlds, such as "Super Earths".

I think there was an article in PopSci about something like this. Except it had to do with the construction of Earthquake resistant structures though.

 

I'll have to reread that for a more comprehensive reply..

If I could please ask you to do so, or provide the reference, that would be much appreciated, thanks !