Some of these earthquakes occur on the surface of the earth, but there are others that arise from within and are captured by seismographs for measurement and study. But these waves are not always destructive, it all depends on the density of the ground where they arise and the speed with which they propagate.
What are P Waves?
P waves refer to the primary seismic movements that occur inside the earth and that are prior to an earthquake, traveling at high speed with a movement parallel to the direction in which the wave propagates.
This primary wave arises when the rocky ground is compressed and expanded again, and can occur in both solid and liquid, through oceans and burning lava from volcanoes, as well as it is possible to feel its effects in the atmosphere, since it can move in the gaseous state, so it can be heard by people and animals as a deep, low sound.
The first vibrations captured by seismographs correspond to P waves, given the speed with which it expands.
What are S Waves?
The S waves are the secondary waves that move transversally with respect to the direction in which the seismic movement propagates. Like the P waves, these occur inside the earth and expand only in a solid medium, since their speed is less than that of the primary waves.
They manifest in the ground after the primary waves, and depending on the mobility capacity of the rocks, what geologists call elasticity, can generate greater change in the ground surface. Its movement goes from top to bottom and from one side to the other, so it shakes the surface of the propagation area, being able to cause great damage to buildings in its path, all depending on the strength of the wave.
Difference Between P and S Waves
- The P or primary waves propagate very quickly in one direction, while the secondary or S waves have slower speeds, so they are captured by seismographs after the P wave.
- The motion of P waves is parallel while that of S waves is transverse.
- With respect to their action on the ground, the P waves compress and dilate the rocky surface; On the other hand, with S waves, depending on the elasticity of the ground and its ability to adapt to movement, significant material damage can be caused to the surface.
- S waves only travel through solid material, unlike S waves that can travel through all three states of matter: solid, liquid, and gas.