1. Earthquakes
Chapter 8

2. Earthquakes What is an earthquake?
(def.) Vibration of Earth produced by a rapid release of energy
Usually along cracks in the earth called faults
Earthquakes usually do not “occur” on the surface
The point where an earthquake occurs is called the focus
The epicenter is the location DIRECTLY above the focus

3. Earthquakes What causes earthquakes?
Rocks in Earth’s crust is stressed and pulled
This action stores elastic energy
Once the build up of energy exceeds the strength of the rock the energy is released
The energy is released as seismic waves

4. Earthquakes Types of seismic waves Surface Waves Body Waves
Travel along the surface of the earth
Move side-to-side AND up and down
Body Waves
Travel through Earth’s interior

5. Earthquakes Two types of Body Waves: P and S P Waves (Primary waves)
Compression waves since they push and pull rocks
Fastest moving seismic wave
Able to move through solid rock and fluids
S Waves (Secondary waves)
Slower than a P wave
Can ONLY move through solid rock
A seismograph is used to detect seismic waves

6. Earthquakes

7. Earthquakes

8. Earthquakes
A typical seismogram of an earthquake:

9. Richter Scale
The Richter scale measures the magnitude of an earthquake
Magnitude refers to the size of seismic waves
A tenfold increase in wave amplitude (height) is equal to an increase of 1 on the scale
Draw back: only useful for shallow earthquakes

10. Continental Drift
German meteorologist, Alfred Wegener, proposed a radical idea: continental drift
Wegener noticed the continents seemed to fit together like pieces of a puzzle
He proposed the continents are “floating” on the molten mantle and were once joined together
This Supercontinent was known as Pangaea

11. Continental Drift Scientists dismissed his theory
Wegener argued that the same fossils are found on different landmasses
Ex. – Mesosaurus on Africa and S. America

12. Continental Drift More supporting evidence:
Similar rock types and structures
Appalachian Mountains were once a large mountain chain like the Rockies
The same types of rocks that are found in North Carolina to NY are found in northern Britain and Scandinavia

13. Continental Drift
The continents of North America, Europe, and Asia were known as Laurasia
South America, Africa, India, Antarctica, and Australia were known as Gondwanaland
The ocean south of Asia was called the Tethys Sea
The rest of the water on Earth was called Panthalassa
The remnants of this ocean is the Pacific

14. Panthalassa Gondwanaland Laurasia

15. Seafloor Spreading

16. Seafloor Spreading
Seafloor spreading refers to the process by which plate tectonics produce new oceanic crust
Where is this taking place?
Atlantic Ocean
Eastern Africa?

18. Seafloor Spreading
Rift valleys are found along the center of the mid-ocean ridges.
Place where magma is forced upwards
Oceanic ridges are areas where the seafloor is elevated due to seafloor spreading
The seafloors are spreading at a rate of 5 cm/year
This means the ocean basins are no older than 200 million years old