1. Earthquakes
And
Volcanoes

2. Defining Earthquakes Shaking and trembling of the earth’s crust.
The waves travel in all directions
More than 1,000,000 occur a year or one every 30 seconds
Faulting is the most common cause
Earthquakes continue until all the energy is used up
TSUNAMIS- earthquake on the ocean floor: causing waves to become greater than 20 meters high

3. Three Types of Faults Strike-Slip Thrust Normal Three types of faults
Form depending on type of plate motion and complex reaction of earth’s lithospheric blocks
Strike-slip
Normal
Thrust
Normal

4. 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

5. What causes earthquakes?
Tectonic plates move past each other causing stress. Stress causes the rock to deform
Plastic deformation – does not cause earthquakes
Elastic deformation – rock stretches then reaches a breaking point, releasing energy.

6. Elastic Rebound – deformed rock goes back to its original shape

7. Focus –. point inside the Earth where an
Focus – point inside the Earth where an earthquake begins Epicenter – point on Earth’s surface above focus

8. Seismic Waves FOCUS- underground point of origin
EPICENTER- aboveground of origin; most violent shaking occurs at the epicenter
The three main types of seismic waves are: P waves, S waves, and L waves

9. P Waves Primary waves Arrive first at the epicenter
Can travel through solids, liquids, and gases
They are push-pull waves

10. S Waves Secondary waves
Can travel through solids, but NOT through liquids and gases
Move in up-down motion

11. Comparing Seismic Waves

12. R and L Waves Surface waves Slowest moving seismic waves
Travel on top of Earth’s surface
Cause most of damage to Earth, because they bend and twist the surface

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

14. Surface Waves Move along the Earth’s surface
Produces motion in the upper crust
Motion can be up and down
Motion can be around
Motion can be back and forth
Travel more slowly than S and P waves
More destructive

15. 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.

16. John Milne- 1893 Seismograph-measures and detects seismic waves
Seismogram- Paper record of waves
Seismologist- scientist who study earthquakes
Richter Scale- a scale that allows scientists to determine earthquake strength based on many readings
1-10 levels at which an earthquake is measured on amount of damage caused; Above a 6 is very destructive

17. Typical Seismogram

18. How are Earthquakes Measured? Richter Scale

19. 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

20. How are Earthquakes Measured? Mercalli Intensity Scale
Click Link for Interactive Demo

21. Earthquake Waves & Earth’s Interior

22. Tsunamis

23. Formation of a tsunami

24. Tsunami Warning System

25. VOLCANOES
Volcano- place on Earth’s surface that allows magma and other material to erupt
Magma- found beneath the Earth’s surface, it is liquid rock
Lava- magma that reaches the Earth’s surface

26. Volcanic Fragments
Volcanic Dust- less that 0.25 mm in diameter (flour)
Volcanic Ash- more than 0.25 less than 5 mm (rice)
Volcanic Bombs- few cm to several meters.
Cinders- volcanic bombs the size of golf balls

27. Types of Volcanoes
Cinder Cones- made of mostly of cinders; formed from explosive eruptions
Shield- Made of quiet lava flows
Composite- made up of alternating layers of rock particles; explosive eruptions, then quite lava flows

28. Volcanic Terminology
Crater- funnel shaped pit, or depression at top of volcano
Caldera- when a crater becomes too large, it collapses: also can form when the top of a volcano collapses or explodes
Dormant- sleeping volcano
Extinct- not known to have erupted in modern history
Active- Erupts fairly regularly

29. Ring of Fire

30. Zones
There are 3 zones:
Ring of Fire- Extends nearly all the way around the edge of the Pacific Ocean
Mediterranean Sea- Italy, Greece, Turkey
Iceland and Atlantic Ocean- Mid Atlantic Ridge

31. EXTRA! EXTRA!
Mount St. Helens is a volcano is Washington State
San Andreas Fault in California
New Madrid Fault is where we live