question_answer 26)

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 ,and that of P wave is 8.0 km . 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, how far away does the earthquake occur ?  

Answer:

Let be the velocities of S waves and P waves, and  be the time taken by these waves to travel to the position of seismograph. If / is the distance of occurrence of earthquake from the seismograph, then                                    ??.(i)                 Now,  and  ?.(ii)                     or                   Also,   min = 240 s                 Using (ii),                                                    Now, from (i) Hence earthquake occurs 1920 km away from the seismograph.