Question

The earth has a radius of 6400 km. the inner core of 1000 km radius is solid. Outside it, there is a region from 1000 km to radius of 3500 km which is in molten state. Then again from 3500 km to 6400 km the earth is solid. Only longitudinal (P) waves can travel inside a liquid. Assume that the P wave has a speed of 8 km s^-1 in in solid parts and of 5 km s^-1 in liquid parts of the earth. An earthquake occurs at some place close to the surface of the earth. Calculate the time after which it will be recorded in a seismometer at a diametrically opposite point on the earth if eave travels along diameter?

Answer 1

In liquid speed of wave = 5 km/s

Time required = \(\frac{Distance}{speed}\)

Time = [ \(\frac{1000-0}{8}+\frac{3500-1000}{5}+\frac{6400-3500}{8}\) ] × 2

Time = [ \(\frac{1000}{8}+\frac{2500}{5}+\frac{2900}{8}\) ] × 2

Time required = 1975 sec

Time required = 32 min 55 sec.