Question

Earthquakes generate sound waves inside the earth. Unlike a gas, the earth can experience both transverse (S) and longitudinal (P) sound waves. Typically the speed of S wave is about 4.0 km s¯¹, and that of P wave is 8.0 km s–1. A seismograph records P and S waves from an earthquake. The first P wave arrives 4 min before the first S wave. Assuming the waves travel in straight line, at what distance does the earthquake occur ?

Answer 1

Given, the speed of sound waves S and P are 4  km/s and 8  km/s respectively. The wave P arrives 4 min before the wave S.

The time gap between the waves P and S is,

Δt=4 min× 60 s 1 min =240 s

The distance of the earthquake is given by the equation,

x= v p ×Δt

Substituting the values in the above equation, we get:

x=8  km/s ×240 s =1920 km

Thus, the earthquake occurs at a distance of 1920 km.