Earthquakes: vibrations of the ground caused by the sudden release of energy stored in rocks
Mostly due to sudden movement along faults
    also, can be due to volcanism

elastic rebound theory:  rocks bend until their strength exceed, break and "snap back"

vibrations (seismic waves) radiate through the earth

focus: location within the earth where rupture begins
epicenter: point on earth's surface directly above the focus

two types of seismic waves:
body waves travel through the earth:
        Primary (P) waves, compression and expansion, travel fastest
        Secondary (S) waves. shear waves, don't travel through liquids
surface waves move only on the surface of the earth

Seismographs: measure and record seismic waves
 

Earthquake distribution

95% of earthquakes are located along plate boundaries.
 two major belts: circum-Pacific, Meditterranean-Asiatic

5% intraplate. Why intraplate?

• adjustments within a plate to the deformation taking place along the edges
• ancient plate boundaries.

Earthquake and Plate Tectonics
divergent boundaries: shallow (< 70 km), due to tension
transform: San Andreas fault system
convergent:
collision: due to compression
subduction zones: due to friction between subducting plate and overlying plate.

Earthquake intensity and magnitude

•  intensity: amount of damage
• magnitude (the Richter scale)
• based on size of largest wave

• logarithmic scale: each increase in magntude is a 10X increase in wave size, 30X increase in energy released

Damage due to earthquakes
depends on magnitude and duration of shaking

•  #1 groundshaking

•  Fires (broken gas lines)
•  Mass movement (landslides, avalanches)

 tsunamis: seismic sea waves
triggered by disturbance of the sea floor
llittle affect in deep water

Earthquake prediction
Long range

• use pattern of past earthquakes to determine when/where next eq is expected (seismic gap). History from human record + evidence of past earthquakes preserved in geologic record (ex: disturbance of sediments, evidence of tsunamis)

• observations of change in shape of earth's surface
•  fluctuations in well water levels
• foreshocks
• changes in animal behavior?

Earthquake control ?

• trigger small eq's by pumping in water?