Seismology
Seismology is the study of the solid earth’s motions, usually called waves. Wave motion can be started by explosions, earthquakes, landslides and thumpers. The earth supports two main types of waves: body waves and surface waves. The body waves go through the earth while the surface waves, like ocean waves, travel on the earth’s surface. Body waves are of two types: P waves or primary waves are longitudinal, like sound waves, which vibrate along the direction of travel; picture a slinky moving like an accordian. P waves travel through the earth at about 6 km/sec. They can go straight through the earth even through the liquid core. S or Shear or Secondary waves travel about 3.5 km /sec and they vibrate with a motion perpendicular to the direction of travel of the wave. Picture the same slinky vibrating up and down instead of back and forth. These S waves cannot penetrate the liquid core but bounce off the core- mantle boundary. It was this property that allowed scientists to discover the earth’s liquid outer core. Diagram from Wikipedia 
The top set depicts P or longitudinal waves, similar to sound waves with the particles moving in the direction of the wave travel.
The bottom set depicts S or shear or transverse waves with the particles moving at right angles to thedirection of the wave travel.Surface waves, which cause the greatest damage, travel on the earth’s surface; again there are two types: Love waves are transverse and cause shaking up and down on the surface. Finally, Rayleigh waves are longitudinal and cause back and forth motion of the ground. Diagram from Wikipedia 
The top set depicts Love or horizontal transverse shear waves, with the ground moving back and forth .
The bottom set depicts Rayleigh or longitudinal waves with the ground moving vertically up and down.
To Geology From Seismology
|
