Question

An earthquake emits both S-waves and P-waves which travel at different speeds through the Earth. A P=wave travels at 9000 m/s and an S-wave travels at 5000 m/s. If the P-waves are received at a seismic station 1 minute before an S-wave arrives, how far away is the earthquake center?

Answer 1

Let distance of the station be 'd' from the center of the earthquake.

Let time taken by P waves to reach the station be 't' s

So time taken by S waves to reach the station = (t+60)s

d = t*9000...(1)

Also, d=(t+60)*5000.......(2)

Dividing (2) by (1) , we get:-

9000t-5000t = 300000

=> 4000 t = 300000

=> t = 75 s

Substituing the value of t=75 s in (1), we get:-

d=75*9000 = 675000 m =675 km.