1. Questions of the Day 2/28/2017
What is the difference between the epicenter of an earthquake and the focus of an earthquake?

2. List processes involved in plate tectonics
Convection currents in the mantle (temperature and density differences)
Different densities of crustal plates – oceanic and continental
Composition and chemical properties of types of rocks – magnetic, formation differences, % elements/ type
Time- how fast the plates move: different plates rate of speed, and different times rate of speed
Magnetic fields – inside and outside of the earth structure
Now scientists believe Wegeners proposal of Pangaea because there is evidence and cause and effect data

3. Types of plate boundaries
Plate tectonics is currently the most unifying geophysical theory of the planet dynamics, based on the interactions between the earth’s interior and its outer shell.
Lithosphere plates move, break up, collide, slide past one another to form new continents and oceans.
Plate movement is a direct result of convection currents in the mantle
Plates interact in one of three ways: divergence, convergence, and lateral sliding
Materials from plates are recycled at subduction zones/ mid ocean ridges

4. Global Distribution of Earthquakes…why here?
Map of world
Dots are earthquakes
Not scattered all over the world, but make a pattern

5. Earthquakes and plate movement
What is the deepest recorded earthquake on the border of SA?
Explain how we know where the mantle ends and the core begins?
How do we know the elemental make up in each layer?
Earthquake data helps figure out the distances/ depths of the inner earth features based on how S and P waves travel to different testing locations. We can also interpret the information based on basic earth composition to determine density readings and know what is where.

6. Earthquake terms:
Earthquake - movement of the ground caused by the release of energy from a sudden shift of rocks in Earth's crust. Fault - a break in Earth's crust where movement of rock (and quakes) occur

7. Elastic rebound theory:
Earthquakes are produced by the rapid release of energy stored in rock that has been subjected to great forces. When the strength of the rock is exceeded, it suddenly breaks, releasing energy as seismic waves.

8. More quake terms:
Focus - the point below Earth's surface where movement of rock produces an earthquake; where an earthquake starts Epicenter - the point on Earth's surface directly above the focus of an earthquake

9. Earthquake energy:
When tectonic plates move they sometimes generate energy at their boundaries and that shock wave is known as a seismic wave. Seismometers (a.k.a. seismographs) are used to measure seismic waves, but those waves are not always detectable.

10. Seismographs

11. Seismogram = ?
The graph output by a seismograph. It is a record of the ground motion at a measuring station as a function of time.

12. Body Seismic wave types:
P waves: primary (first) waves which are push-pull in nature (compressional) S waves: secondary waves which shake particles at right angles to their direction of travel (transverse)

13. Two types of waves are measured
How do each of the waves travel differently?
Explain why some stations do not receive S waves.
Because of the composition of the inner earth, waves travel at different speeds or can not travel at all. Density differences can be assessed, as well as depth and other information from these waves.

14. What are S and P waves? •Seismographs – record movement and waves
Surface waves – travel along the outer layers of the earth
Body waves – travel through the earth’s interior
•P waves ( push pull waves) ( like a spring): can move through solid rock or fluids. Fastest seismic wave.
P-wave Animation
•S waves travel at right angles ( like a rope): can only move through solid rock. Slower than p-wave.
S-wave Animation
Earthquakes were 1st studied by the Chinese over 2000 yrs ago, Hmm why would they be interested?
Connect early science information and understanding with the cultures that were first to make observations ( China, Asia are on the boundary of the W Pacific trenches)

15. Surface seismic waves:
Travel along Earth’s outer layer, causing ground movement similar to how ocean waves toss a ship. x
How do scientists locate earthquakes? By measuring the arrival time of P and S waves (whose velocities are known) earthquakes can be triangulated.

16. Reading a Seismograph Which are the P waves and which are the S waves?
Which type of wave would arrive at a location 1st?
What causes them to arrive at different times?
Students should identify the type of wave and its movement to reference why it would arrive first/ second; using this difference in times is how scientists determine how far away the origin of the shock wave was. By looking at each distance, triangulation can be used to locate the focus and epicenter of the earthquake.

17. Which station did was closer to the Epicenter?
Which was farthest away?
How do you know? (use evidence to explain)

18. Seismographs ---- record S and P wave arrival at a specific station
- how is this information useful to determine the origin of the earthquake??
Consider the seismicity maps and the data we reviewed - if each station has it’s own set of data, that means we could do what?

19. Rate of wave travel -Why do S and P waves travel at different rates?
- How did the the ability to measure S and P waves help us understand what is in the center of the earth?
One of the other ways to report and measure Earthquake information is the Mercalli scale.

21. Two different scales to measure
Mercalli scale - perception based
1884 became “modified” and again later
quantifies effects of the earthquake and damage caused using roman numerals
Numbering from
Human perspective/ reports of damage
Have students look at the reference sheets for Mercalli and read a few in class to get an idea of how it works, before looking at the Hogswallow activity.

22. Hogwallow to Rattlesburg
Use the reports from residents to identify the strength of earthquake waves at each location.
Where does the epicenter seem to be?
What was the highest rating reported?
What is your overall impression of use of this scale? (pros and cons)