Seismology is the examine of earthquakes and seismic waves that transfer by and across the earth. A seismologist is a scientist who research earthquakes and seismic waves.
Seismic waves are the waves of vitality brought on by the sudden breaking of rock throughout the earth or an explosion. They’re the vitality that travels by the earth and is recorded on seismographs.
There are a number of completely different sorts of seismic waves, they usually all transfer in numerous methods. The 2 fundamental kinds of waves are physique waves and floor waves. Physique waves can journey by the earth’s inside layers, however floor waves can solely transfer alongside the floor of the planet like ripples on water. Earthquakes radiate seismic vitality as each physique and floor waves.
Touring by the inside of the earth, physique waves arrive earlier than the floor waves emitted by an earthquake. These waves are of a better frequency than floor waves.
The primary type of physique wave is the P wave or main wave. That is the quickest type of seismic wave, and, consequently, the primary to ‘arrive’ at a seismic station. The P wave can transfer by stable rock and fluids, like water or the liquid layers of the earth. It pushes and pulls the rock it strikes by identical to sound waves push and pull the air. Have you ever ever heard an enormous clap of thunder and heard the home windows rattle on the identical time? The home windows rattle as a result of the sound waves have been pushing and pulling on the window glass very similar to P waves push and pull on rock. Generally animals can hear the P waves of an earthquake. Canines, for example, generally start barking hysterically simply earlier than an earthquake ‘hits’ (or extra particularly, earlier than the floor waves arrive). Often individuals can solely really feel the bump and rattle of those waves.
P waves are also called compressional waves, due to the pushing and pulling they do. Subjected to a P wave, particles transfer in the identical route that the the wave is transferring in, which is the route that the vitality is touring in, and is typically referred to as the ‘route of wave propagation’. Click on right here to see a P wave in motion.
Determine 1 – A P wave travels by a medium via compression and dilation. Particles are represented by cubes on this mannequin. Picture ©2000-2006 Lawrence Braile, used with permission.
The second kind of physique wave is the S wave or secondary wave, which is the second wave you’re feeling in an earthquake. An S wave is slower than a P wave and may solely transfer by stable rock, not by any liquid medium. It’s this property of S waves that led seismologists to conclude that the Earth’s outer core is a liquid. S waves transfer rock particles up and down, or side-to-side–perpendicular to the route that the wave is touring in (the route of wave propagation). Click on right here to see a S wave in motion.
Determine 2 – An S wave travels by a medium. Particles are represented by cubes on this mannequin. Picture ©2000-2006 Lawrence Braile, used with permission.
If you would like to strive your hand at making your individual P and S waves, do that little experiment.
Travelling solely by the crust, floor waves are of a decrease frequency than physique waves, and are simply distinguished on a seismogram in consequence. Although they arrive after physique waves, it’s floor waves which are virtually enitrely answerable for the injury and destruction related to earthquakes. This injury and the energy of the floor waves are diminished in deeper earthquakes.
The primary type of floor wave is known as a Love wave, named after A.E.H. Love, a British mathematician who labored out the mathematical mannequin for this sort of wave in 1911. It is the quickest floor wave and strikes the bottom from side-to-side. Confined to the floor of the crust, Love waves produce fully horizontal movement.Click on right here to see a Love wave in motion.
Determine 3 – A Love wave travels by a medium. Particles are represented by cubes on this mannequin. Picture ©2000-2006 Lawrence Braile, used with permission.
The opposite type of floor wave is the Rayleigh wave, named for John William Strutt, Lord Rayleigh, who mathematically predicted the existence of this sort of wave in 1885. A Rayleigh wave rolls alongside the bottom identical to a wave rolls throughout a lake or an ocean. As a result of it rolls, it strikes the bottom up and down, and side-to-side in the identical route that the wave is transferring. A lot of the shaking felt from an earthquake is as a result of Rayleigh wave, which could be a lot bigger than the opposite waves. Click on right here to see a Rayleigh wave in motion.
Determine 4 – A Rayleigh wave travels by a medium. Particles are represented by cubes on this mannequin. Picture ©2000-2006 Lawrence Braile, used with permission.
Figures 1 by 4, in addition to wave animations, are ©2000-2006 Lawrence Braile, used with permission. All different content material is ©2007 Michigan Technological College. Permission granted for replica for non-commercial makes use of.