how many earthquakes occur each year??
DESCRIPTION
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. Stress. - PowerPoint PPT PresentationTRANSCRIPT
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?