When it happens, some of the energy it releases is converted into heat inside the earth. Some of the energy is expended on cracking and permanently deforming rocks and minerals along the fault. The rest of the energy, i.e., most of the energy, radiates out from the hypocenter in the form of a wave.
*Waves are divided into two main categories: body waves (P and S waves) that pass through the Earth's interior and surface waves that only propagate on the Earth's surface.
Body waves pass through the interior of the earth. There are two types of body waves: p-waves and s-waves.
The p in the p-wave stands for primary because they are the fastest waves and they are detected first once the p-wave occurs. P-waves travel through the Earth's interior many times faster than jet planes, taking only a few minutes to travel through the Earth.
P-waves are mainly compressive waves. When a longitudinal wave passes through, the material compresses in the same direction as the direction in which the wave is moving, and then extends back to its original thickness after the wave passes. The velocity at which the p-wave travels through the material is determined by:
Rigidity - How well the material resists lateral bending and is able to straighten itself once the shear force has passed - The more rigid the material, the faster the p-waves.
Compressibility – The material can be compressed into a smaller volume and then return to its original volume after the compressive force has passed;The higher the compressibility of the material, the faster the p-waves.
Density – how much mass the material contains per unit volume;The denser the material, the slower the longitudinal waves.
The animation below shows the propagation of p-waves on a plane (left) and from a point source (right).
P-waves can pass through both solids and liquids and gases. Although liquids and gases have zero rigidity, they are compressible, which allows them to transmit longitudinal waves. Sound waves are p-waves that travel through the air.
Since the mantle becomes harder and compressible as the depth below the asthenosphere increases, the deeper the longitudinal wave travels in the mantle, the faster it travels. The density of the mantle also increases with the increasing depth below the asthenosphere. Higher density reduces the speed of the wave. However, the effect of increased stiffness and compressibility in the deep mantle is much greater than that of increased density.
The s in the S wave represent the secondary waves because they are the second fastest waves and the second detected waves after they occur. Although transverse waves are slower than longitudinal waves, they still travel fast, more than half the speed of longitudinal waves, traveling thousands of kilometers per hour through the earth's crust and mantle.
The s-wave is a shear wave (although this is not what the s represents). They move by the material being bent or deformed (sheared) sideways from the direction of wave propagation, and then return to its original shape after the wave passes. The speed at which a transverse wave travels through a material is determined only by the following factors:
Rigidity – how well a material resists lateral bending and is able to straighten itself once the shear force has passed – the more rigid the material, the faster the transverse waves.
Density – how much mass the material contains per unit volume – the greater the density of the material, the slower the shear waves.
The animation below shows the propagation of the s-wave on a plane (left) and a point source (right).
S-waves can only pass through solids because only solids are rigid. Transverse waves cannot pass through liquids or gases.
Since the mantle becomes harder as the depth below the asthenosphere increases, the deeper the transverse wave travels in the mantle, the faster it travels. The density of the mantle also increases at greater depths, which has the effect of decreasing the speed of the wave, but the increase in stiffness is much greater than the increase in density, so the transverse wave accelerates deeper in the mantle, although the density increases.
There are two types of surface waves: Rayleigh waves and Love waves. Rayleigh Wave is named after the English aristocrat Lord Rayleigh (John Stratt), who, in his work as a scientist and mathematician, made detailed mathematical calculations of the type of surface wave named after him. Rayleigh waves are caused by the combined effect of longitudinal and transverse waves on the Earth's surface.
Rayleigh waves are sometimes referred to as rolling waves. In Rayleigh waves, the earth's surface rises and sinks in the form of crests and troughs, similar to waves on the surface of water. People who are outdoors when the big ** occurs usually see Rayleigh waves moving across the earth's surface and can feel the undulations of the ground as Rayleigh waves pass underneath them.
Lovewaves, sometimes called L-waves, are named after the English mathematician and physicist Augustus Love, who first modeled the waves mathematically. Love waves involve a transverse shear of the surface and then revert to its original form as each wave passes by.
All surface waves propagate slower than body waves, and Rayleigh waves propagate slower than Ralph waves.