Solution:
Solution:
Velocity of the S waves is v1 = 4.5 km/s. The velocity of the P waves is v2 = 8.0 km/s.
Let the time taken by the S and P waves to reach the seismograph be t1 and t2 . It is given that
t1 - t2 = 4 min = 4 × 60 = 240 sec ... (i)
Let the distance of the epicentre (km) be S. Then
S = v1 t1 = v2t2
$$\Rightarrow 4.5\times t_{1}-8t_{2}=0 \Rightarrow t_{2}=.4.58t_{1}$$ ... (ii)
Using (i) and (ii)
$$t_{1}-t_{2}=240 \Rightarrow t_{1}\left(1-\frac{4.5}{8}\right)=240$$
$$\Rightarrow t_{1}=\frac{240\times8}{3.5}=548.5 s.$$
$$\therefore S = v_{1}t_{1} = 4.5 × 548.5 = 2468.6 \approx 2500$$ km.