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 P-waves are received at a seismic station 1.00 minute before an S-wave arrives, how far away is the earthquake centre?
A)88.9 km
B)1200 km
C)675 km
D)240 km
E)480 km

Question

Quizplus · Accepted Answer

Let the distance from the seismic station to the earthquake centre be "d".
We know that time taken by P-wave to travel this distance is "d/9000".
And time taken by S-wave to travel this distance is "d/5000".
Given, P-wave arrives 1.00 minute before S-wave.
So, (d/9000) - (d/5000) = 1.00
Solving this equation, we get d = 675 km. 
Therefore, the answer is C.

An Earthquake Emits Both S-Waves and P-Waves, Which Travel at Different