earthquakes. earthquakes are natural vibrations of the ground, caused by: fractures in earths crust...
TRANSCRIPT
Earthquakes
Earthquakes
Earthquakes are natural vibrations of the ground, caused by: Fractures in earth’s crust Volcanic eruptions
Stress and Strain
Stress causes fractures in rock
Three types of stress: Compression Tension Shear
Deformation caused by stress is known as strain
Compression
Compression is stress that decreases the volume of material
Tension
Tension is stress that pulls a material apart
Shear
Shear is stress that causes a material to twist
Effects of Strain and Stress
Stress and strain can cause deformation
Low stresses cause elastic strain Elastic strain causes a material
to bend and stretch Can return to normal, like a
rubber band High stresses cause ductile
deformation Material is permanently
deformed Can cause breaks or failure
Faults
When stress causes rock to fail, a fault occurso Fault – Fracture(s) along
which movement occurs
Three main types of faults: Reverse Normal Strike-Slip (Transform)
Reverse Fault
Reverse Faults are fractures that result from horizontal compression
Shortens crust horizontally
Normal Fault
Normal Faults are fractures caused by horizontal tension
Lengthens crust horizontally
Strike-Slip Fault
Strike-Slip Faults are fractures caused by horizontal shear
Motion is mainly horizontal
Earthquake Waves
Vibrations of the ground during earthquakes are called Seismic Waves
Three types: Primary Wave (P-Wave) Secondary Wave (S-Wave) Surface Waves
P-Waves
P-Waves squeeze and pull rocks in the same direction as the wave travels
S-Waves
S-Waves cause rocks to move at right angles to the direction of the wave
Surface Waves
Surface Waves move rocks up and down, as well as side-to-side
Motion is similar to an ocean wave
Focus
Earthquakes originate at a point called a Focus
Focus is usually below the surface The Epicenter is the point on Earth’s surface
directly above the focus