# When an earthquake occurs, two types of sound waves are generated and travel through the earth. The primary, o?

Jan 02, 2011
in
Earthquake Questions

When an earthquake occurs, two types of sound waves are generated and travel through the earth. The primary, or P, wave has a speed of about 10.5 km/s and the secondary, or S, wave has a speed of about 5.5 km/s. A seismograph, located some distance away, records the arrival of the P wave and then, 140 s later, records the arrival of the S wave. Assuming that the waves travel in a straight line, how far is the seismograph from the earthquake?

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One comment

DH on January 2, 2011 at 7:20 am

Let t be the time for the P wave so t + 140 is the time for the S wave

Since each travels the same distance we have

10.5t = 5.5*(t + 140)

so 5t = 770

or t = 770/5 = 154s

Therefore x = 10.5km/s*154s = 1617km