As rock interface are crossed, the elastic characteristics encountered (by seismic waves)generally change abruptly, which causes part of the energy to be reflected back to the surface, where it is recorded by seismic instruments.

　　当岩石界面被穿过的时候，震波所遇到的弹性性质通常会发生突然的变化，这就使得一部分能量被反射回地面，在地面反射回来的波被震波纪录仪记录下来。