Primary waves are identical in character to sound waves. The ground is forced to move forwards and backwards as it is compressed and decompressed.

主要波跟声波的特征相同，当地面被加压或减压时强迫向前和向后移动。

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P-waves are sometimes known as primary waves, because they travel faster through the Earth and so are the first to arrive at monitoring stations.

P波有时被看作纵波，因为它们以更快的传递速度穿越地球内部，因此最先被地震监测站台发现。

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Detecting the primary waves from an earthquake is like seeing the flash of lightning before hearing the thunder and getting drenched by the rain.

探测到一次地震的初波就好比要在听到雷声并且被雨淋透之前看到闪电。

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Since the primary waves travel more quickly than the comparatively sluggish secondary waves, the system picks up on the magnitude and speed at which the quake is approaching, and beams the data over fiber optic networks to emergency relay stations setup in corporate towers, governmental buildings, hospitals, and transportation venues such as railways.

ENGADGET: Japan Meteorological Agency develops earthquake warning system