Chapter 11, Problem 12Q

How did geophysicists determine that part of the Earth's interior is liquid?

To determine

How did geophysicists determine that part of the Earth’s interior is liquid?

Answer to Problem 12Q

Solution:

Theydetermine that the Earth’s interior is molten or liquid by using the P-waves which are detected in the inner core.

Explanation of Solution

A seismic event (Earthquake)produces longitudinal and transverse waves. Both types of waves can travel through a solid medium, since both atoms and molecules are able to vibrate in any direction around their relatively fixed positions.

Longitudinal waves or compression waves are known as P-waves (P by the pressure)and transverse waves are called S-waves (by the term shear).

In longitudinal waves, the particles move in the same direction of propagation of the wave, compressing and expanding the rock successively. The transverse waves, on thsse other hand, shake the particles at right angles to the direction in which they travel.

Since any transverse type movement will not experience any restoring force, since the fluids are easily deformable, the transverse waves do not propagate through the fluids unlike the longitudinal waves. After the telluric event, only the longitudinal waves are detected diametrically on the Earth. This action allowed the geophysicists to deduce that a part of the interior (nucleus)of the Earth contains fluid or is liquid.

Seismic waves travel at different speeds, even in the same medium. The fastest in propagating are the longitudinal waves, which arrive first at a seismological station than the transverse ones, and the interval time between the arrival of the P-waves and the arrival of the S-waves, will be a function of the distance between the station and the epicentre.

Conclusion:

Only theP-waves let geophysicists detect liquid in the inner core of the Earth where, generally, waves travel more slowly, and the areas are very hot.