Chapter 17, Problem 32PQ

Problems 32 and 33 are paired.

N Seismic waves travel outward from the epicenter of an earthquake. A single earthquake produces both longitudinal seismic waves known as P waves and transverse waves known as S waves. Both transverse and longitudinal waves can travel through solids such as rock. Longitudinal waves can travel through fluids, whereas transverse waves can only be sustained near the surface of a fluid, not inside the fluid. When seismic waves encounter a fluid medium such as the liquid outer core of the Earth, only the longitudinal P wave can propagate through. Geophysicists can model the interior of the Earth by knowing where and when S and P waves were detected by seismographs after an earthquake (Fig. P17.32). Assume the average speed of an S wave through the Earth’s mantle is 5.4 km/s and the average speed of a P wave is 9.3 km/s. After an earthquake, a seismograph finds that the P wave arrives 1.5 min before the S wave. How far is the epicenter from the detector?

FIGURE P17.32