What does a seismogram show?

A seismogram of a real earthquake event (a Magnitude 8.3 event in the Kuril Islands).

A seismogram is the wiggly trace that records the vibrations caused by an earthquake at a particular recording station.

Once you know what some parts of a seismogram show, you can start to understand how seismologists can use seismograms to learn more about earthquakes.

  1. The seismogram is based on data from Eskdalemuir seismic recording station. What is the location of Eskdalemuir (Latitude and Longitude values) shown on the screenshot?
  2. This seismogram shows information for a particular earthquake, at Latitude 46.683°, Longitude 153.224°, Depth 27.7km. Find this information on the screenshot, then write down the information given in the line below it: this line below it tells you the distance from the earthquake to the recording station in degrees. (A degree is equivalent to about 111km on the Earth's surface.)
  3. The horizontal axis shows time in minutes since an identified time (11.00.00 UTC in this example). For the chosen earthquake event, the predicted arrival times for the first P-waves and S-waves at this location are as follows: P-waves 11:26:13; S-waves 11:35:57. Mark the corresponding ''wiggles' on the screenshot.
  4. As well as P-waves and S-waves ('body' waves), there are also surface waves, which are much slower. Mark the zone on your seismogram corresponding to the first group of surface waves, and label these 'Love waves'. Mark the zone corresponding to the second group of surface waves, labelling this 'Rayleigh waves'.
  5. The average frequency content of the different wave types in this plot is 0.2 Hz for P-waves, 0.05 Hz for S-waves and 0.01 Hz for Surface waves. In the crust, P-waves have an average velocity of 6.5 km/sec, S-waves 3.7 km/sec and surface waves 3.5 km/sec. What is the wavelength of these different wave types in the crust?

Teachers' notes

What does a seismogram show?What does a seismogram show?

Students identify some features of a real seismogram.