When a wave emanating from the surface reaches a boundary between two media that have different acoustic impedance (the product of density and velocity), some of the energy is reflected back into the upper medium.

• 当一个从地面激发的波动到达具有不同声波组抗（速度与密度之乘积）的两种介质之间的分间面时，其部分能量将被反射并回到上覆介质中。