1. Forces that Shape Earth
The shaking or trembling caused by the sudden release of energy
Usually associated with faulting or breaking of rocks
Continuing adjustment of position results in aftershocks

2. Stress and Strain
Most earthquakes occur when rocks fracture, or break, deep within Earth.
Fractures form when stress exceeds the strength of the rocks involved.
Stress is the forces per unit area acting on a material.
Strain is a change in the shape of a rock caused by stress.

3. Stress and Strain
There are three kinds of stress that act on Earth’s rocks:
1.) Tension
Stress that pulls a material apart.
Pulls on the crust, stretching rock so it becomes thinner in the middle

4. Stress and Strain
There are three kinds of stress that act on Earth’s rocks:
2.) Compression
Stress that decreases the volume of a material.
Squeezes rock until it folds or breaks

5. Stress and Strain
There are three kinds of stress that act on Earth’s rocks:
3.) Shear
Stress that causes a material to twist.
Pushes a mass of rock in two opposite directions

6. Landforms created by Compression
Mountain Ranges- collision between two continental plates
The Himalayas

7. Landforms created by Compression
Ocean Trenches- more dense plate goes under the less dense plate during collision forming a deep trench
Mariana’s Trench

8. Mariana Trench

9. Landforms created by Compression
Volcanic Island Arcs- curved line of volcanoes that form parallel to plate boundaries
Aleutian Islands

10. Landforms created by Tension
Mid-ocean Ridges- tension causes oceanic crust to spread allowing hot rock from mantle to rise creating high ridges
Mid-Atlantic Ridge

11. Landforms created by Tension
Rift Valleys- continental rifts, when divergent boundaries occur within a continent, they cause enormous splits in the crust.
East African Rift Valley

12. Landforms created by Shearing
Transform Faults- fracture or break in rock, significant displacement as a result of rock mass movement
San Andreas Fault

13. Stress and Strain
Strain- a change in the shape of a rock caused by stress
1.) Elastic strain- change in rock that is NOT permanent, when stress is removed rock goes back to original shape
2.) Plastic/ Ductile strain- creates a permanent change in the shape of a rock, usually occurs when rocks are weak or hot

14. Stress and Strain
There is a distinct relationship between stress and strain that can be plotted as a stress-strain curve.
1.) Low stresses produce the straight segment, which represents the elastic strain of a material.
2.) If the elastic strain is reduced to zero, the deformation disappears.

15. Stress and Strain Ductile Deformation
3.) When stress exceeds a certain value (elastic limit), a material undergoes ductile deformation, shown by the curved segment of the graph.
4.) This type of strain produces permanent deformation, which means that the material stays deformed even if the stress is reduced to zero.

16. Stress and Strain Ductile Deformation
5.) When stress exceeds the strength of a material, the material breaks, or fails, as designated by the X on the graph.
6.) Most rocks, though brittle on the surface, become ductile at the higher temperatures present at greater depths.

17. What is the Elastic Rebound Theory?
Explains how energy is stored in rocks
Rocks bend until the strength of the rock is exceeded
Rupture occurs and the rocks quickly rebound to an undeformed shape
Energy is released in waves that radiate outward from the fault

18. Fault vocab Fault- break in the rock of Earth’s crust
Write these terms on your foldable
Fault- break in the rock of Earth’s crust
Hanging wall- block of rock that lies above the fault
Foot wall- block of rock that lies below the fault

19. Three Types of faults Reverse faults
Form due to compression, shortens crust
Forces push two blocks of rock together with block above fault (hanging wall) moving up relative to the block below fault (foot wall)
Location- convergent plate boundary

20. Three Types of faults Normal faults Form due to tension extends crust
Forces pull tow blocks of rock apart
Block above fault (hanging wall) moves down relative to block above fault
Location- divergent plate boundary

21. Three Types of faults Strike-slip faults Form due to shear stress
Two blocks of rock slide horizontally past one another in opposite directions
Location- transform plate boundary

22. The Focus and Epicenter of an Earthquake
The point within Earth where faulting begins is the focus, or hypocenter
The point directly above the focus on the surface is the epicenter

23. Benioff Zone
Benioff Zone is an area of increasingly deeper seismic activity, inclined from the trench downward in the direction of the island arc.

24. Where Do Earthquakes Occur and How Often?
- 80% of all earthquakes occur along the Pacific Plate known as the circum-Pacific belt
most of these result from convergent margin activity
~15% occur in the Mediterranean-Asiatic belt
remaining 5% occur in the interiors of plates and on spreading ridge centers
more than 150,000 quakes
strong enough to be felt are
recorded each year

25. What are Seismic Waves?
Response of material to the arrival of energy released by rupture
Two types:
Body waves
P and S
Surface waves
R and L

26. Body Waves: P and S waves
P or primary waves
fastest waves
travel through solids, liquids, or gases
compressional wave-material movement is in the same direction as wave movement
S or secondary waves
slower than P waves
travel through solids only
shear waves - move material perpendicular to wave movement

27. Surface Waves: R and L waves
Travel just below or along the ground’s surface
Slower than body waves; Especially damaging to buildings
Two Types:
Rayleigh waves- rolling
Love waves- side-to-side

28. Seismograph records earthquakes events.
Horizontal Seismograph
Vertical Seismograph

29. A seismogram records wave amplitude and time.
Amplitude- maximum height in a peak of a wave
Which waves have the largest amplitude?

30. How is an Earthquake’s Epicenter Located?
Seismic wave behavior
P waves arrive first, then S waves, then L and R
Average speeds for all these waves is known
After an earthquake, the difference in arrival times at a seismograph station can be used to calculate the distance from the seismograph to the epicenter.

31. How is an Earthquake’s Epicenter Located?
Time-distance graph showing the average travel times for P- and S-waves. The farther away a seismograph is from the focus of an earthquake, the longer the interval between the arrivals of the P- and S- waves

32. Triangulation: Locating an Epicenter
Three seismograph stations are needed to locate the epicenter of an earthquake
A circle where the radius equals the distance to the epicenter is drawn
The intersection of the circles locates the epicenter

33. Clues to Earth’s Interior
Seismic waves change speed and direction when they encounter different materials in Earth’s interior.
P-waves and S-waves traveling through the mantle follow fairly direct paths.
P-waves that strike the core are refracted, or bent, causing P-wave shadow zones where no direct P-waves appear on seismograms.
S-waves do not enter Earth’s outer core because they cannot travel through liquids and do not reappear beyond the P-Wave shadow zone.

34. Clues to Earth’s Interior

35. Clues to Earth’s Interior
This disappearance of S-waves has allowed seismologists to reason that Earth’s outer core must be liquid.
Detailed studies of how other seismic waves reflect deep within Earth show that Earth’s inner core is solid.

36. Earthquake Magnitude and Intensity
Magnitude is the measurement of the amount of energy released during an earthquake.
The Richter scale is a numerical scale based on the size of the largest seismic waves generated by a quake that is used to describe its magnitude.
Each successive number in the scale represents an increase in seismic-wave size, or amplitude, of a factor of 10.
Each increase in magnitude corresponds to about a 32-fold increase in seismic energy.

37. Earthquake Magnitude and Intensity
Modified Mercalli Scale
The modified Mercalli scale, which measures the amount of damage done to the structures involved, is used to determine the intensity of an earthquake.
This scale uses the Roman numerals I to XII to designate the degree of intensity.
Specific effects or damage correspond to specific numerals; the higher the numeral, the worse the damage.

38. Earthquake Magnitude and Intensity

39. Earthquake Magnitude and Intensity
Modified Mercalli Scale
Earthquake intensity depends primarily on the amplitude of the surface waves generated.
Maximum intensity values are observed in the region near the epicenter; Mercalli values decrease to I at distances very far from the epicenter.
Modified Mercalli scale intensity values of places affected by an earthquake can be compiled to make a seismic-intensity map.

40. Earthquake Magnitude and Intensity
Depth of Focus
Earthquake intensity is related to earthquake magnitude.
The depth of the quake’s focus is another factor that determines the intensity of an earthquake.
An earthquake can be classified as shallow, intermediate, or deep, depending on the location of the quake’s focus.
A deep-focus earthquake produces smaller vibrations at the epicenter than a shallow-focus quake.

41. Classification According to Focus Depths

42. How are the Size and Strength of an Earthquake Measured?
Magnitude
Richter scale measures total amount of energy released by an earthquake; independent of intensity
Amplitude of the largest wave produced by an event is corrected for distance and assigned a value on an open-ended logarithmic scale

43. What are the Destructive Effects of Earthquakes?
Damage in Oakland, CA, 1989
Building collapse
Fire
Tsunami
Ground failure

44. Ground Shaking
Amplitude, duration, and damage increases in poorly consolidated rocks.

45. EARTH DESTRUCTION
Liquefaction - Unconsolidated materials saturated with water turn into a mobile fluid.
Seiches - These are the rhythmic sloshing of water in lakes, reservoirs, and enclosed basins. The waves can weaken reservoir walls and cause destruction.

46. Earth Destruction
Landslides and ground subsidence – Whenever the land moves quickly, as with landslides, there is the potential for a lot of damage and potential loss of life.
Fire – Ruptured gas lines from earthquakes is one of the major hazards.
Ground Rupture ‐ This refers to areas where the land splits apart causing a rupture. These are often long linear features.
Ground shaking versus material type – More ground shaking occurs in poorly consolidated (loose) sediments than solid bedrock.

47. Tsunamis
A tsunami is a large ocean wave generated by vertical motions of the seafloor during an earthquake.
These motions displace the entire column of water overlying the fault, creating bulges and depressions in the water.
The disturbance spreads out from the epicenter in the form of extremely long waves that can travel at speed over 800 km/h (500 mph).
When the waves enter shallow water they may form huge breakers with heights occasionally exceeding 30 m (19 ft.).

48. Formation of a Tsunami
Tsunami waves can travel at a speed of over 500 mph.

49. Can Earthquakes be Predicted?
Earthquake Precursors
changes in elevation or tilting of land surface, fluctuations in groundwater levels, magnetic field, electrical resistance of the ground
seismic dilatancy model
seismic gaps

50. Can Earthquakes be Predicted?
Earthquake Prediction Programs
include laboratory and field studies of rocks before, during, and after earthquakes
monitor activity along major faults
produce risk assessments