Key Terms: seismograph, seismometer, seismogram,
S-P interval, amplitude
Detecting Seismic Waves
 Please turn to page 119 in your textbook.
 Seismograph
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An instrument used to record and measure seismic waves.
Records the ground movements caused by seismic waves as they
move through the earth.
Records the P waves, S waves, and Surface waves.
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How a Seismograph Works
 As the animation is being shown, read
the captions. You may also want to make
a quick sketch in your notes.
 Animation
 The paper record produced by the
seismograph is called the seismogram.
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Reading the Seismogram
 A highly simplified simulated recording of
earthquake waves (a seismogram) will be shown
on the next slide. Label the handout of the sample
seismogram and be sure you can identify these
parts:
 P-waves and the P-wave arrival time
 S-waves and the S-wave arrival time
 S-P interval or S-P lag time (expressed in seconds)
 S-wave maximum amplitude (measured in mm)
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P Wave Arrival
Time
S Wave
Arrival Time
Amplitude
S-P Interval
Time in Seconds
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Seismogram Animation
 As the animation is being shown, watch and identify
these parts:
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P-waves and the P-wave arrival time
S-waves and the S-wave arrival time
S-P interval (also known as the S-P lag time)
 Animation
 On the next slides, we will be trying to determine the
S-P interval for 2 different seismograms.
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Calculate the S-P Interval (lag time)
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56 Seconds
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Calculate the S-P Interval
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44 Seconds
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Stop
 Complete Using the S-P interval on a
seismogram to determine the distance to the
epicenter of an earthquake activity before
continuing.
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