Describe the different types of earthquake waves
Answers
Answer:
Types of wave
Seismic waves are fundamentally of twotypes, compressional, longitudinal waves or shear, transverse waves. Through the body of the Earth these are called P-waves (for primary because they are fastest) and S-waves (for secondary since they are slower).
Answer:
When an earthquake happens deep underground a crack will start to open on a pre-existing line of weakness in the Earth's brittle crust. This crack will then grow larger and larger, relieving built-up stress as it goes.
The speed at which the crack propagates or grows is 2–3 km/sec. Eventually the rupture will cease to grow and will slow down and stop. The size or magnitude of the earthquake depends upon how much the fault has ruptured (the slip) and also the area over which the rupture has occurred.
This rupturing process creates elastic waves in the Earth that propagate away from the rupture front at a much faster speed than the rupture propagates, the exact speed depends upon the nature of the wave (a longitudinal or P-wave is faster than a transverse or S-wave), and on the elastic properties of the Earth. As you go deeper into the Earth, the density and pressure increases and so do the velocities of seismic waves.
Types of wave
Seismic waves are fundamentally of two types, compressional, longitudinal waves or shear, transverse waves.
Through the body of the Earth these are called P-waves (for primary because they are fastest) and S-waves (for secondary since they are slower). However, where a free surface is present (like the Earth–air interface) these two types of motion can combine to form complex surface waves.
Although often ignored in introductory texts, surface waves are very important since they propagate along the surface of the Earth (where all the buildings and people are) and usually have much higher amplitudes than the P-waves and S-waves. It is usually surface waves which knock down buildings.
Seismic waves, like all waves, transfer energy from one place to another without moving material.
Summary of seismic wave types and properties
Type (and names) Particle motion Typical velocity Other characteristics
P
Compressional Primary
Longitudinal Alternating compressions ('pushes') and dilations ('pulls') in the same direction as the wave is propagating VP ~ 5 – 7 km/s in typical Earth's crust :
>~ 8 km/s in Earth's mantle and core; 1.5 km/s in water; 0.3 km/s in air P motion travels fastest in materials, so the P-wave is the first-arriving energy on a seismogram. Generally smaller and higher frequency than the S and surface waves. P-waves in a liquid or gas are pressure waves, including sound waves