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