AS SEISMIC WAVES TRAVEL FROM MATERIAL OF ONE SPEED AND DENSITY TO ANOTHER

THE INCIDENT WAVES ARE REFLECTED AND TRANSMITTED (REFRACTED)

BOTH THE ANGLES AND SIZE (AMPLITUDE) OF THE WAVES CHANGE, DEPENDING ON THE VELOCITY AND DENSITY CHANGE

THIS EFFECT LETS US STUDY EARTH STRUCTURE

(AND IS USED IN LENSES, EYEGLASSES, ETC. FOR LIGHT)