A longitudinal earthquake wave strikes a boundary between two types of rock at a 35 degree angle. As it crosses the boundary, the specific gravity (SG = d_rock / d_water ) of the rock changes from 3.7 to 2.8. Assuming that the elastic modulus is the same for both types of rock, determine the angle of refraction.

To solve this I have two equations.

1) (velocity 1/ velocity 2) = (sine angle 1 / sine angle 2), a ratio

2) velocity of an earthquake wave = sq. root ( elastic modulus / density )

The problem I'm having is, I don't know what the elastic modulus is and what the density or (rho) is, and also density is supposed to = m/v

Otherwise, I could solve this easily...

Can anyone help?