How are Earthquakes Located?

Novice Spanish

We can locate earthquakes using a simple fact: an earthquake creates different seismic waves (P waves, S waves, etc.) The different waves each travel at different speeds and therefore arrive at a seismic station at different times. P waves travel the fastest, so they arrive first. S waves, which travel at about half the speed of P waves, arrive later. A seismic station close to the earthquake records P waves and S waves in quick succession. With increasing distance from the earthquake the time difference between the arrival of the P waves and the arrival of the S waves increases. This basic approach to locating quakes is illustrated using an example of an earthquake near Mexico.

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  • Different waves each travel at different speeds and therefore arrive at a seismic station at different times.    
  • Difference in arrival times between P and S waves can be used to determine the distance between the station and an earthquake. 
  • By knowing how far away the quake was from three stations we can draw a circle around each station with a radius equal to its distance from the earthquake. The earthquake occurred at the point where all three circles intersect. 


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GIFS for select segments included as optional download.

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