1. Section 1: Earth’s Crust in Motion How Do Stress Forces Affect Rock?
The movement of earth’s plates creates powerful forces that squeeze or pull the rock in the crust – these forces are examples of stress
Stress – a force that acts on rock to change its shape or volume
An earthquake is the shaking and trembling that results from the movement of rock beneath earth’s surface

2. How Does Stress Effect the Earth’s Crust?
Deformation – any change in the volume or shape of earth’s crust
Three kinds of stress in the crust:
Shearing – stress that pushes a mass of rock in two opposite directions
Tension – pulls on the crust, stretching rock so that it becomes thinner in the middle like warm bubble gum
Compression – squeezes rock until it folds or breaks like a giant trash compactor

3. What Is a Fault?
Fault – a break in earth’s crust where slabs of crust slip past each other; These usually occur at plate boundaries

4. What Kind of Faults Are There?
Three Kinds:
Strike-slip faults
Normal Faults
Reverse Faults

5. What Are Strike-slip Faults?
Shearing forces cause rocks to slip past each other sideways with little up and down Motion;
Ex. San Andreas fault in California

6. Tension forces cause the rocks to form the fault at an angle
What Are Normal Faults?
Normal faults
Tension forces cause the rocks to form the fault at an angle
One block is above the fault
Hanging wall – the half of the fault that lies above
Footwall – the half of the fault that lies below
Ex. Rio Grande rift valley

7. What Are Reverse Faults?
compression forces cause the rocks to move towards each other
Same structure as normal fault but the blocks move in opposite direction; hanging wall move up
Ex. Appalachian Mountains and Mount Gould in Glacier National Park

8. B A A miner walks on the foot wall and looks up at the hanging wall!
Hanging wall moves down
Hanging wall moves up
What type of fault?
What type of fault?
Normal Fault
Reverse Fault

9. How Are Mountains Effected by These Forces?
Fault-block mountains – normal faults uplift a block of rock
Folding – bends in the rock that form when compression shortens and thickens part of the earth’s crust. Ex. Himalayas

10. How Are Mountains Effected by These Forces? (Continued)
Anticlines – a fold upward into an arch
Syncline – a fold downward into an arch
Plateaus – a large area of flat land elevated high above sea level

11. Earthquakes – most begin in the lithosphere
Section 2: Measuring Quakes How Does the Energy of an Earthquake Travel Through Earth?
Earthquakes – most begin in the lithosphere
Focus – the point beneath the earth’s surface where rock that is under stress breaks, triggering an earthquake
Epicenter – the point on the earth’s surface directly above the focus

12. What Are Seismic Waves?
Seismic Waves – vibrations that travel through Earth carrying the energy released during an earthquake
They move like ripples on a pond
They carry the energy of an earthquake away from the focus, through Earth’s interior, and across the surface
The energy is greatest at the Epicenter

13. What Are the Different Kinds of Seismic Waves?
Three categories:
P waves
S waves
Surface waves
P waves and S waves are sent out from the focus; Surface waves develop when the waves reach the surface

14. What Are P Waves? P waves are primary waves The first waves to arrive
Earthquake waves that compress and expand the ground like an accordion
Cause buildings to contract and expand

15. Cannot move through liquids
What Are S Waves?
S waves are secondary waves
Earthquake waves that vibrate from side to side as well as up and down
These waves shake the ground back and forth
Shake structures violently
Cannot move through liquids

16. What Are Surface Waves?
When P waves and S waves reach the surface some are transformed into surface waves
Surface waves move more slowly than P waves and S waves
Produce the most severe ground movements
Can make the ground roll like ocean waves or shake buildings from side to side

17. How Do Scientists Detect Seismic Waves?
                  
How Do Scientists Detect Seismic Waves?
Seismograph – records the ground movements caused by seismic waves as they move through the Earth

18. How Do Scientists Measure Earthquakes?
There are at least 20 different measures for rating earthquakes, three are:
Mercalli
Richter
Moment Magnitude
Magnitude – a measurement of earthquake strength based on seismic waves

19. What Is the Mercalli Scale?
Rated earthquakes according to their intensity
Intensity: strength of ground motion in a given place
Not a precise measurement
Describes how earthquakes affect people, buildings, and the land surface

20. What Is the Richter Scale?
A rating of the size of seismic waves as measured by a particular type of seismograph
Accurate measurements for small, nearby earthquakes not large, distant earthquakes

21. What Is the Moment Magnitude?
A rating system that estimates the total energy released by an earthquake
Can be used to rate earthquakes
of all sizes, near or far
Below 5.0 – little damage
Above 5.0 – great destruction

22. How Do Scientists Locate the Epicenter?
Geologists use seismic waves
P waves arrive first
S waves arrive close behind
Scientist measure the difference in arrival times
The farther away an earthquake is the greater the time between their arrival
Scientists draw three circles using data from seismographs set at different stations to see where they intersect – the epicenter