Earthquakes produce several types of shock waves. The most well-known are the P-waves (P for primary or pressure) and the S-waves (S for secondary or shear). In the earth's crust, the P-waves travel at around 6.5 km/s while the S-waves move at about 3.5 km/s. The actual speeds vary depending on the type of material they are going through. The time delay between the arrival of these two waves at a seismic recording station tells geologists how far away the earthquake occurred.

Question

If the time delay is 33s, how far from the seismic station did the earthquake occur?

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Answer 1

distance = speed * time
d = 6.5 t
d = 3.5 (t+33)

6.5 t = 3.5 t + 115.5
t = 38.5 seconds
d = 6.5 * 38.5 = 250.25 km

Answer 2

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