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Given the difference in arrival times, you can determine the distance from the epicenter.
Technically you just need one, but the more there are, the easier it is to locate the epicenter of the earthquake. The reason for this is that based on the timing of each of the three seismic waves that reach the station, the station can calculate a radius all around the station. So picture a circle with what the radius is around the station, another station will do the same thing, and there HAS TO BE an intersection of these circles somewhere, so that narrows down the location of the epicenter. Hope this makes sense.
The first waves to arrive at a seismograph station are primary waves, or P waves.
S-waves will take 31 seconds P-waves will take 8 minutes
Your standing on it! P-waves travel faster than S-waves through the Earth. As such the further away a seismometer station is from the epicentre of an Earthquake, the larger the difference between arrival times will be. By the same logic this means that the closer you get to the epicentre, the smaller the difference in arrival time will be until your at the epicentre when the difference will be zero!
Given the difference in arrival times, you can determine the distance from the epicenter.
The difference in arrival times of P and S waves.
The distance of an epicenter from a seismograph station can determined by the time it takes for the seismic waves to reach each station. You need at least 3 seismic stations to record the event to determine this. The time taken for each seismic station to resisted the event will be different as they are different distances from the epicenter. The distance to the epicenter can then be calculated for each station and a epicenter can be determined by a triangulation from all stations that have registered the event.
Technically you just need one, but the more there are, the easier it is to locate the epicenter of the earthquake. The reason for this is that based on the timing of each of the three seismic waves that reach the station, the station can calculate a radius all around the station. So picture a circle with what the radius is around the station, another station will do the same thing, and there HAS TO BE an intersection of these circles somewhere, so that narrows down the location of the epicenter. Hope this makes sense.
The P waves vibrate very quickly out from the epicenter first in all directions, in a circular way passing the station.The S waves then vibrate out from the epicenter a few seconds later and cause the sideways shaking of the land as they pass the station.The P wave then reflects off the core of the Earth and bounces back past the station, followed by the S wave a few seconds later because both waves reflect off the earths core back to the epicenter.
P waves
Using the difference in their arrival times and an estimate of their velocity of propagation you can calculate the distance of the earthquake epicentre from the seismometer recording station. If you do this from three or more different seismometer stations you can triangulate it's position. For more information please see the related question.
They get weaker as they travel out from the epicentre
Radio Waves - radio station - was created in 2010.
As P-waves travel at a higher velocity than S-waves they arrive at a seismometer station before the S-waves. The difference between their arrival time can be used to calculate the distance from the seismometer station to the epicentre.
The first waves to arrive at a seismograph station are primary waves, or P waves.
S-waves will take 31 seconds P-waves will take 8 minutes