Question

A seismograph station is located 2000 km from an earthquake’s epicenter. Explain the order that the S and P waves will arrive at the station by using the characteristics of the waves.

Answer 1

Answer:

The P waves undergoes compression and dilation during motion in its direction of propagation. This waves reaches the station first because the P waves travels at a speed, that is much faster in comparison to the S waves. The S waves are the secondary waves and are commonly known as the shear waves.

The P waves have the ability to travel in both solid as well as in liquid, whereas the S waves can propagate only in solid region because they are absorbed at the core-mantle boundary.

Thus, the P waves will arrive the station first and the difference between the arrival of P and S waves are plotted in the graph that helps in depicting the epicenter and the amount of energy released during an earthquake.

Answer 2

The P waves vibrate very quickly out from the epicenter first in all directions, in a circular way passing the station. The S waves then vibrate out from the epicenter a few seconds later and cause the sideways shaking of the land as they pass the station. The P wave then reflects off the core of the Earth and  bounces back past the station, followed by the S wave a few seconds later  because both waves reflect off the earths core back to the epicenter.