Thread: Elastic modulus, earthquake waves?

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?

Originally Posted by realintegerz

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?

the problem says that the elastic modulus is the same for both types of rock, so it will cancel in the equation.






you also know the respective SG's ...







note that the value for water density also cancels ...



you should be able to finish up