What role does the s-p interval play in locating an earthquake epicenter?

Not sure

ANSWER:

The time difference between the 'first S wave' and the 'first P wave' helps in determining the distance of the 'seismic station' from the epicenter.

EXPLANATION:

This S-P interval can be used to calculate the 'magnitude of the earthquake' once it is used to determine 'how many millimeters the ground moves' at the seismic station. This measurement can be done when the distance between the epicenter and the seismic station is known. The S-P interval helps to know the actual distance and thereby by plotting the time interval and the distance, the 'magnitude of the earthquake' at the epicenter can be known.  

Geologists use  seismic waves to  locate an earthquake's epicenter.. 

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