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Earth and Space Sciences · 术语表

什么是 P wave; S wave？

又称： P wave · S wave

Definition 11.1 High School Earth and Space Sciences · 第 11 章 — Seismic Waves Reveal the Interior

A P wave is a seismic wave that alternately compresses and stretches the rock: the rock moves back and forth along the direction in which the wave travels. It crosses solids, liquids and gases, and it is the fastest seismic wave, so it arrives first. An S wave shears the rock: the rock moves at right angles to the direction in which the wave travels. It crosses only solids, and it arrives after the P wave.

Seismologists of the Puerto Rico Seismic Network and of the USGS install a temporary seismometer in south-western Puerto Rico, on 10 January 2020. Photograph: Thomas Pratt, USGS (public domain).

示例

Example 11.4 (An earthquake $60{}^{\circ}$ away)

Observed travel times are $608\,\mathrm{s}$ for P and $1101\,\mathrm{s}$ for S at $60{}^{\circ}$ , $536\,\mathrm{s}$ and $967\,\mathrm{s}$ at $50{}^{\circ}$ . A station that records an S wave $493\,\mathrm{s}$ (8 minutes 13 seconds) after the P wave therefore lies $60{}^{\circ}$ from the epicentre: about $60 \times 111.2 \approx 6670\,\mathrm{km}$ . At $50{}^{\circ}$ the delay would only be $431\,\mathrm{s}$ .

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