1. Earthquakes
Section 2.3

2. Alaska Earthquake of 1964 Watch Video: http://goo.gl/2Q24Cr
What was its reading on the Richter scale?
What caused it to happen?

3. Caused by the movement of the Pacific plate in relation to the North American plate
FAULT: crack in Earth’s crust due to the motion of one tectonic plate relative to another

4. Elastic energy is stored in rock and as the stress builds between two tectonic plates the potential energy increases
Just like stretching an elastic band
When the energy stored is too great, the rock gives and the plates shift
In the case of the Alaskan earthquake, the Pacific plate was subducted (pushed under) the North American plate
FOCUS: the location of an earthquake
EPICENTRE: (b/c earthquakes originate underground) it is the point on Earth’s surface directly above the focus

5. Watch “Subduction” Video
Review terms:
Lithosphere
Asthenosphere
Oceanic crust
Continental Crust
Seismic Waves
New terms:
Focus
Fault
Epicenter

6. Using the terms from before, fill in the following diagram:
fault, focus, epicenter, lithosphere, asthenosphere, oceanic crust, continental crust, seismic waves

7. Types of Seismic Waves PRIMARY WAVES (P-Waves):
Pass through rock as a series of compressions and expansions and are able to pass through solids, liquids or gases
Think of an accordion, or a slinky being pushed back and forth
P-waves move faster than S-waves
Move longitudinally, parallel to the Earth

8. SECONDARY WAVES (S-Waves):
Travels through rock in a traditional wave motion, having crests and troughs; can only pass through solids
Think of as a slinky as you move it up and down
S-waves have a shearing force and twist rocks up, down, left and right
Move transversely, perpendicular to Earth
S-waves transfer more energy and therefore are more destructive

9. SURFACE WAVES (Earth-Waves):
Travels along the Earth’s surface
Behaves much like an S-wave but moves much slower
Do the most damage of all three because they are responsible for the ground shaking (and buildings can only withstand minimal ground shaking)
See pg. 348 for a summary of the three types of waves

10. Studying Earthquakes
P-waves are the waves that geologists are most interested in, especially when searching for petroleum
As depth increases, the speed of both P and S – waves increases
Any sudden changes in rock properties cause waves to change direction quickly

11. Changes in seismic waves as they pass through Earth

12. What is the Richter scale?
Number that shows the intensity of an earthquake
Based on the amount of vertical ground movement at its epicentre
An earthquake of 3.0 is barely detectable by people.

13. What are tsunamis?
Seismic sea wave triggered by an earthquake in or near an ocean (often incorrectly called a tidal wave)

14. Now it’s your turn…
Complete pg. 349 # 17-18
Pg. 351 # 1-5