What are Earthquakes?

  • P waves are the first waves to be recorded by a Seismograph, followed by the S waves and then surface waves.
  • The further the Seismograph is from the source of the earthquakes, the longer the lag time between the P waves and S waves
  • A travel – time graph shows the relationship b/w P and S wave arrival times and the distance from an earthquakes epicenter

Locating the Epicenter

  • Since a Seismograph tells scientist the distance to an earthquake, it does not tell them the exact location of the earthquake
  • To determine the exact location of an earthquake, we need to know the distances from at least three different stations in order to plot an epicenters location
  • After getting data from three stations, draw a circle from the station, the point at which all three circles meet is the epicenter

Measuring an Earthquakes Magnitude

  • The magnitude of an earthquake can also be measured using the seismogram.
  • The scale of earthquake magnitude was introduced by Charles F Richter in 1935
  • So each increase in a whole number in the Richter magnitude is 31 times more powerful than the last number
  • ie – magnitude 7 is 31 more powerful than a magnitude 6

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