A major earthquake centered on Lorna Prieta, California, near San Francisco, occurred at 5:04 P.M. local time on October 17, 1989 (in UTC, Coordinated Universal Tune, 0h 4m 15s on October 18, 1989). The primary seismic waves (P waves) from such an earthquake are longitudinal waves that travel through the earth's crust. P waves were detected at Caracas, Venezuela, at 0h 13m 54s UTC; at Kevo, Finland, at 0h 15m 35s UTC; and at Vienna, Austria, at 0h 17m 02s UTC. The distances the P waves traveled from Lorna Prieta were 6280 km to Caracas, 8690 km to Kevo, and 9650 km to Vienna.
(a) Use the arrival times to calculate the average speed of the P waves that traveled to these three cities. How can you account for any differences between the average speeds? (b) The average density of the earth's crust is about 3.3 g/cm3• Use this value to calculate the bulk modulus of the earth's crust along he path traveled by the P waves to each of the three cities. How do our answers compare to the bulk modulus in Table 11.l?