An earhquake generates both transverse (S) and logitudinal (P) sound wave in the earth .The speed of (S) wave is about `4.5km//s` and that of (P) wave is about `8.0km//s` A seismograph records P and S wave from an earthquake. The first P wave arrives `4.0 min` before the first S wave. The epicenter of the earthquake is located at a distance of about

Options

A. `25 km`
B. `250 km`
C. `2500 km`
D. `5000 km`

Answer

C

Explanation

`d`: distance of epicentre
`d = v_(p) t_(p) = v_(s)t_(s) or 8t_(p) = 4.5 t_(s) rArr t_(p) = (4.5)/(8) t_(s)`
`t_(s) - t_(p) = 4 xx 60`
`t_(s)(1-(4.5)/(8)) = 240 rArr t_(s) = 548.5 s`
`d = v_(s)t_(s) = 4.5 xx 548.5 ~= 2500 km`