How many Earthquakes Occur each year??

More than 1 million !!!

What are Earthquakes?

Vibrations of the earth’s crust caused by a sudden release of

energy

What causes EQ’s?

Build up of stress along the boundaries of tectonic

plates

StressStress = the total force acting on

crustal rocks per unit of area

3 Kinds of stress 1. Compression – decrease volume2. Tension – pulls apart3. Shear – twist Example : sponge

Strain How rocks respond to stress is

called strain Strain = deformation of a

material expressed in rocks by folding (bending)

or faulting (breaking)

Elastic Rebound Theory

Describes the process between stress & strain

Elastic Rebound Theory• 2 sides along a fault

are locked by friction • Energy in the form of

stress is stored in rock

• When stress exceeds frictional lock, movement occurs

• Energy is released in form of waves

• Rocks rebound to original shape

Elastic Rebound Theory Demo:

Wood blocks, sandpaper, and rubber bands, can model the slow storage and rapid

release of elastic energy

In Class

• Read text p 528 – 530• Define stress & strain

ANY QUESTIONS?

How many Earthquakes Occur each year??

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Transcript of How many Earthquakes Occur each year??

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