Seismic Waves
The main seismic wave types are Compressional (P), Shear (S), Rayleigh (R) and Love (L) waves. P and S waves are often called body waves because they propagate outward in all directions from a source (such as an earthquake) and travel through the interior of the Earth. The P and S waves are shown propagating horizontally, parallel to the Earth’s surface. Love and Rayleigh waves are surface waves and propagate approximately parallel to the Earth’s surface. Although surface wave motion penetrates to significant depth in the Earth, these types of waves do not propagate directly through the Earth’s interior. Descriptions of wave characteristics and particle motions for the four wave types are given in Table.P Wave: The deformation (a temporary elastic disturbance) propagates. Particle motion consists of alternating compression and dilation (extension). Particle motion is parallel to the direction of propagation (longitudinal). Material returns to its original shape after the wave passes.S Wave:The deformation (a temporary elastic disturbance) propagates. Particle motion consists of alternating transverse motion. Particle motion is perpendicular to the direction of propagation (transverse). The transverse particle motion shown here is vertical but can be in any direction; however the Earth’s approximately horizontal layers tend to cause mostly SV (in the vertical plane) or horizontal (SH) shear motions. Material returns to its original shape after the wave passes.
Rayleigh Wave:
The deformation (a temporary elastic disturbance) propagates. Particle motion consists of elliptical motions (generally retrograde elliptical as shown in the figure) in the vertical plane and parallel to the direction of propagation. Amplitude decreases with depth. Material returns to its original shape after the wave passes.
The deformation propagates. Particle motion consists of alternating transverse motions. Particle motion is horizontal and perpendicular to the direction of propagation (transverse). To best view the horizontal particle motion, focus on the Y axis (red line) as the wave propagates through it. Amplitude decreases with depth. Material returns to its original shape after the wave passes.
Department of Physical Science and Engineering 4700 King Abdullah University of Science and Technology Thuwal 23955-6900 Saudi Arabia. |
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