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