Question

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 8.0 km/s and the secondary, or S, wave has a speed of about 4.5 km/s. A seismograph, located some distance away, records the arrival of the P wave and then, 95.7 s later, records the arrival of the S wave. Assuming that the waves travel in a straight line, how far (in terms of m) is the seismograph from the earthquake?

Answer 1

Dp = Ds
Vp*T = Vs*(T+95.7)
8*T = 4.5*(T+95.7)
8T = 4.5T+430.65
8T-4.5T = 430.65
3.5T = 430.65
T = 123 s.

D = Vp*T = 8 * 123 = 984 km.