The information will travel like the compressional wave ahead of an earthquake, detectable only by special equipment.

这些信息将地震前的纵波一样传播，只有特殊设备才能检测到。

These are longitudinal waves that have to travel through a medium.

这些是必须通过介质传播的纵波。

In the case of a longitudinal wave, the back-and-forth motion is more of a compression-and-expansion.

在纵波的，来运是压缩和膨胀。

Sound, you'll recall, is a wave: a 'longitudinal' wave.

如前所述，声音是一种波： 纵波。

But there are also longitudinal waves, where the oscillations happen in the same direction as the wave is moving.

但是也有纵波，其中振荡发生在与波移的方向相同的方向上。

So the p wave and the s wave, and the different phases that move out from the site of rupture in the earth, are used by seismologists to locate the event.

地震学家用纵波、横波以及地球破裂部位移出的不同阶段来定位地震发生地点。

But sound is the other kind of wave: it’s a longitudinal wave, meaning that the wave’s back-and-forth motion happens in the same direction in which the wave travels.

但声音是另一种波：它是一种纵波，这意味着波的来运发生在与波传播相同的方向上。