TYPES OF EARTHQUAKE WAVES
Earthquake shaking and damage is the result of three basic types of elastic waves. Two of the three propagate within a body of rock.
The fastest of these body waves is called the primary or P wave. Its motion is the same as that of a sound wave in that, as it spreads out, it alternately pushes (compresses) and pulls (dilates) the rock. These P waves are able to travel through both solid rock and liquid material, such as volcanic magma or the water of the oceans.
The slowest wave through the body of rock is called the secondary or S wave. As an S wave propagates, it shears the rock sideways at right angles to the direction of travel. If a liquid is sheared sideways or twisted, it will not spring back, so S waves cannot propagate in the liquid parts of the earth
The third general type of earthquake wave is called a surface wave, reason being is that its motion is restricted to near the ground surface. Such waves correspond to ripples of water that travel across a lake.
Surface waves in earthquakes can be divided into two types. The Love or L wave is a type of surface wave along with Rayleigh wave. The L’s motion is essentially that of S waves that have no vertical displacement; it moves the ground from side to side in a horizontal plane but at right angles to the direction of propagation. The horizontal shaking of Love waves is particularly damaging to the foundations of structures.
