GARY HINCKS / SCIENCE PHOTO LIBRARY GARY HINCKS / SCIENCE PHOTO LIBRARY
Seismograph trace. Artwork of a printout (seismogram) from a seismograph machine. A seismograph records the intensity of ground movements caused by seismic activity. When an earthquake or tremor occurs, a pen in the seismograph transfers the movement onto a paper drum. The resulting graph shows the amplitude of the seismic (shock) waves over time (lines show 5 minute intervals). The first waves received during an earthquake are (from left to right) primary (P) body waves, followed by secondary (S) body waves, and lastly, the surface waves, which are of greatest magnitude and cause the most damage.
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