Question: How are seismic waves used to determine the position and thickness of Earth's interior layers? Need Assignment Help? View Available Hint(s)for Part A Dense rock layers will allow seismic waves to pass straight through them. Dense rock layers will slow the velocity of seismic waves and allow them to pass straight through with no deflection. Dense interior layers will increase the velocity of seismic waves and change their direction through refraction. Lower density layers will increase the velocity of seismic waves. Dense rock layers will increase the velocity of seismic waves.