Earthquakes produce several types of shock waves. The most well-known are the P-

Question

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 center tells geologists how far away the earthquake occurred. If the time delay is 73 s, how far from the seismic station did the earthquake occur?

Explanation / Answer

D = Pt
D = S(t+73)
because P travels the same distance in t seconds as S does in t + 73 seconds. Subtract the second equation from the first to get
0 = Pt - St - 73S
t = 73S/(P - S)
and substitute into the first equation to get
D = 73PS/(P - S)
and finally substitute the actual numbers to get
D = (73)(6.5)(3.5)/(6.5 - 3.5) = 553.6 km

Related Questions

Navigate

• Browse (All)
• Browse E
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.