Seismic waves
- 2. Seismic waves • Seismic waves are the waves of energy caused by the sudden breaking of rock within the earth or an explosion. • Response of material to the arrival of energy fronts released by rupture. • Energy that travels through the earth and is recorded on seismographs.
- 3. Seismic waves defined by: • Where they move –Earth’s interior vs. Surface • How they move –vertically vs. Horizontally • How fast they move –meters per second
- 4. Types of Seismic Waves • There are several different kinds of seismic waves, and they all move in different ways. – Body waves – Surface waves. • Body waves can travel through the earth's inner layers, but surface waves can only move along the surfaces like ripples on water. • Earthquakes radiate seismic energy as both body and surface waves.
- 5. • Two types: –Body waves • P or Primary waves • S or Secondary waves –Surface waves • Love waves • Rayleigh wave
- 6. Body Waves • Travelling through the interior of the earth, body waves arrive before the surface waves emitted by an earthquake. • These waves are of a higher frequency than surface waves.
- 7. P or Primary waves • The first kind of body wave is P wave or primary wave. • This is the fastest kind of seismic wave, and, consequently, the first to arrive at a seismic station. • P wave can move through solid rock and fluids, like water or the liquid layers of the earth. • It pushes and pulls the rock it moves through just like sound waves push and pull the air.
- 8. • P waves are also known as compressional waves, because of the pushing and pulling they do. • Subjected to a P wave, particles move in the same direction that the wave is moving in, which is the direction that the energy is travelling in, and is called the direction of wave propagation.
- 10. S or Secondary waves • The second type of body wave is the S wave or secondary wave, which is the second wave you feel in an earthquake. • S wave is slower than a P wave and can only move through solid rock, not through any liquid medium. • It is this property of S waves that led seismologists to conclude that the Earth's outer core is a liquid. • S waves move rock particles up and down, perpendicular to the direction that the wave is travelling in (the direction of wave propagation).
- 12. SURFACE WAVES • Travelling through the crust, surface waves are of a lower frequency than body waves, and are easily distinguished on a seismogram as a result. • Though they arrive after body waves, it is surface waves that are almost enitrely responsible for the damage and destruction associated with earthquakes. • This damage and the strength of the surface waves are reduced in deeper earthquakes.
- 13. LOVE WAVES • The first kind of surface wave is called a Love wave, named after A.E.H. Love, a British mathematician who worked out the mathematical model for this kind of wave in 1911. • It's the fastest surface wave and moves the ground from side-to-side. • Confined to the surface of the crust, Love waves produce entirely horizontal motion.
- 15. RAYLEIGH WAVES • The other kind of surface wave is the Rayleigh wave, named for John William Strutt, Lord Rayleigh, who mathematically predicted the existence of this kind of wave in 1885. • A Rayleigh wave rolls along the ground just like a wave rolls across a lake or an ocean. Because it rolls, it moves the ground up and down, and side- to-side in the same direction that the wave is moving. • Most of the shaking felt from an earthquake is due to the Rayleigh wave, which can be much larger than the other waves.