Section 11.1 Notes - Forces Inside Earth
Elastic Limit
– The limit to how far something can bend
– When reached, something will break
Fault – Surfaces rocks move along when they break
Fault Movement
1) Up
2) Down
3) Sideways
What Causes Faults?
The movement of plates – movement puts stress on the rocks near
the plate edges.
What can a rock do to relieve stress?
1) Bend
2) Compress
3) Stretch
4) Break – if the force is great enough
Earthquake –
- The vibrations produced by the breaking of rock
- Occur near plate boundaries
How Earthquakes Occur
- Forces drive rocks to move
- Rocks bend and change shape
- When the elastic limit is met, rocks break, move along the
fault, and return to the original shape
- Earthquake occurs
Types of Forces
Tension – pulls rocks apart
Compression – squeezes rocks together
Shearing – rocks slide past each other
Normal Fault
- Tension pulls rocks apart – divergent
- Rock above the fault moves down in relation to rock below
the fault
Reverse Fault
- Compression squeezes rock – convergent
- Surface is pushed up and over the rock below
Strike-Slip Fault
- Rocks move past each other – transform
- No up or down movement
- Example – San Andreas Fault
Section 11.2 – Features of Earthquakes
Seismic Waves - waves generated by an earthquake
Origin of Seismic Waves
When the elastic limit is exceeded, energy is released in the form of
seismic waves.
Focus –
- Point of energy release
- Seismic waves travel out from here
Types of Seismic Waves
- Primary – P wave – fastest – causes particles in rocks to move
in the same direction as the wave
- Secondary – S wave – causes particles in the rocks to move at
right angles to the direction of the wave
- Surface – slowest – cause the most destruction – move
particles in a backward, rolling and a side to side motion –
travel out from the epicenter
Epicenter – Point on Earth’s surface directly above the earthquake
focus
Speed of Waves
1) Primary
2) Secondary
3) Surface
Seismograph – instrument that measures seismic waves and
records the time they arrive
Structure of Earth
Mantle
- largest layer
- above outer core
- made of Si, O, Mg and Fe
- upper and lower mantle
-
Crust
- outermost layer
- helps make up the lithosphere
- less dense than the mantle
Shadow Zone –
- An area on Earth between 105 degrees and 140 degrees from
the earthquakes focus
- No waves are detected here
Waves and the Liquid Outer Core
Secondary Waves – not transmitted through a liquid – stopped
Primary Waves – slowed and bent, but not stopped
******* This creates the shadow zone!!***********
Moho Discontinuity – boundary between the crust and the upper
mantle