Earth Science

Geological Activity from Plate Tectonics Processes

Measuring Earthquake Magnitude

Study Tip
Seismographs and seismometers are different; seismographs graph information on seismic waves while seismometers simple record ground motions.

Measuring Magnitude

  • Seismographs are machines that receive seismic waves, and write them onto graphs, called seismograms.
  • Since S-waves do not travel through liquids, a seismogram with no S-waves means that the earthquake was on the other side of the Earth from the seismogram.
Study Tip
Seismographs and seismometers are different; seismographs graph information on seismic waves while seismometers simple record ground motions.
Study Tip
The same way a person may cast a shadow over another person when they stand under the sun, planets or celestial bodies that have aligned themselves cast shadows over one another as well.
  • The amplitude of waves can determine the magnitude of the earthquake.
  • Seismograms record a lot of information: the timing of foreshocks, P-waves, S-waves, surface waves, and aftershocks.
  • Seismometers are machines that record ground motions. Modern seismometers are electronic, and keep information stored in computers.
Concept Check
  • What is a seismograph?
  • What is a seismogram, and what does it record?
  • What can a seismogram with no S-waves tell you?
  • What are seismometers?
seismograms
An example showing three seismograms
Concept Check
  • What is a seismograph?
  • What is a seismogram, and what does it record?
  • What can a seismogram with no S-waves tell you?
  • What are seismometers?