An earthquake emits both P-waves and S-waves that travel at different speeds through the Earth. A P-wave travels at 8 000 m/s and an S-wave at 4 000 m/s. If P-waves are received at a seismic station 30.0 s before an S-wave arrives, how far is the station from the earthquake center?

240Km

Explanation:

For each wave, we calculate the time taken to travel the required distance. The time taken for wave P can be computed as

distance=Speed * time

Distance=8000t...........equation 1

For wave S which was received 30secs later the the total time of travel is

(t+30)

Hence the distance covered is

Distance=4000(t+30)............equation 2

If we equate both equations we arrive at

Hence the distance travel by any of the wave will give the required distance

Distance traveled by wave P is from equation 1

Distance=8000t

Distance=8000*30

Distance=240,000m

Distance=240Km