Key Terms: seismograph, seismometer, seismogram, S-P interval, amplitude

Detecting Seismic WavesPlease turn to page 119 in your textbook.

Seismograph 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 WorksAs the animation is being shown, read the captions. You may also want to make a quick sketch in your notes.

AnimationThe paper record produced by the seismograph is called the seismogram.

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Reading the SeismogramA 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

Time in Seconds

S-P Interval

Amplitude

Seismogram AnimationAs the animation is being shown, watch and

identify these parts: 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)

AnimationOn 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)

56 Seconds

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Calculate the S-P Interval

44 Seconds

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StopComplete 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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