Earthquakes


The Behavior of Materials
Stress - a directed force
	Tensile :   < = >
	Compressive :  => <=
	Shear : =>
			<=
Strain : Deformation


Behavior of Materials


Elastic : recoverable strain - stretch a rubber band
Plastic : non recoverable strain - continue stretching until the 
rubber band is permanently deformed
Yield Point : change from elastic to plastic behavior


Failure


Failure can occur while the material is behaving elastically : 
where stress is proportional to strain [linear] -- BRITTLE 
behavior
Failure can occur while the material is behaving as a plastic 
substance : where the relationship between stress and strain is 
curvilinear -- DUCTILE behavior


Dilatancy Model


 "Energy" begins to accumulate in the material undergoing 
strain
Prior to failure the material may begin to develop cracks
Water may enter the cracks and the increased fluid pressure 
further weakens the material
Generation of Earthquakes





Rupture occurs (at the Focus) and energy is released
The place on the Earth closest to the focus is the Epicenter
Energy travels away from the focus - the further it travels, the 
lower the amount of energy remaining



Waves


Body Waves
	Travel in the interior of the Earth
	P waves - Primary
	S waves - Secondary
Surface Waves
	Travel along the surface of the Earth
	Produced when a Body wave "hits" lthe surface : Raleight 
waves and Love waves


P Waves


Primary, Push-Pull
Particles are displaced parallel to the direction of wave 
propagation
Travel with the highest velocity of the body waves
Vp = [4/3(B + G)/Density]1/2
	
Wave Propagation


B : the Bulk Modulus - resistance to a change in volume
	Solids resist attempts to chage their shape
G : the Shear Modulus - resistance to a change in shape
	Liquids have no resistance to a change in shape - G = 0

S Waves


Vs = [G/Density]
Therefore, the velocity of a S wave is 0.0 is the wave 
propagates through a liquid
P and S waves are generated at the focus when an 
earthquake occurs
For any given material Vp > Vs
P waves can travel through a liquid - a reduction in velocity







Size of Earthquakes


Mercalli Scale - a contour map which displays regions of 
equal response to the earthquake - I to XII
Richter Scale - measures amplitude of ground motion - 
Magnitude 5 is 10 times more "intense" than a Magnitude 4.  No 
earthquake has been recorded with a Magnitude 9.


Plate Tectonics


Review Plate Boundaries
Divergent - Spreading Centers - Shallow Focus 
Convergent - Subduction - Shallow, Intermediate - Deep 
Focus
Transform - relatively shallow