1. There is a quiz (not a test) planned for Wedneday.
Topics:
Steno’s Laws
Structural Geology
Groundwater

2. Earthquakes

3. The result of either: Volcanism (movement of magmas within the crust).
Brittle deformation (not plastic) along faults (not folds) in Earth’s crust.

4. Three main sources of Earthquakes:
1) Subduction zones (magma generation) (Andes Mountains).

5. 2) Dip-slip faults (normal and reverse faults) (Arizona, Nevada).

6. 2) Strike-slip faults…left and right lateral (San Andreas in California).

7. Geometry:
Focus: Location where the earthquake occurred inside the Earth.
Epicenter: Point on Earth’s surface directly above the focus.

8. Seismogram

9. The 3 Types of Waves Surface waves- Like water waves. Body Waves:
Primary waves (longitudinal, push-pull)- Vibration direction is parallel to wave motion.
Secondary waves (transverse)- Vibration direction is perpendicular to wave motion.

10. Surface Waves

11. Primary waves (longitudinal, push-pull)- Vibration direction is parallel to wave motion.
Secondary waves (transverse)- Vibration direction is perpendicular to wave motion.

12. Types of Waves: WAVE TYPE SYMBOLISM BEHAVIOR SPEED Surface Waves
Like rolling water waves (mechanical).
Very slow (but damaging).
Primary (P) Body Waves
Push-Pull Waves (longitudinal).
Fast
Secondary (S) Body Waves
Shear Waves (transverse).
Slow

13. Locating Earthquakes
How do we figure out where an earthquake has occurred (find the epicenter or focus)?

14. Seismogram

15. Warmup: Which kid is running faster, A or B?

18. Observations: S-waves travel slowly (top line).
P-waves travel much faster (bottom line).
At t = 0, S and P waves are at the same location (at the focus).
As the distance from the focus increases, t increases. Therefore…
We can use t to determine the distance from our observation station to the earthquake's focus.

20. QUESTION:
How many seismograph observations do we need to locate the epicenter of an earthquake?

21. QUESTION:
How many seismograph observations do we need to locate the epicenter of an earthquake?

22. QUESTION:
How many seismograph observations do we need to locate the epicenter of an earthquake?

27. Arizona Earthquakes Typically of magnitude <4.

28. Earthquake Exercise # 1

29. The New Madrid Fault Zone

30. New Madrid Video Clip https://www.youtube.com/watch?v=hWnBSJQdiSM
(Show only 10 minutes as an introduction)

31. Earthquake Activity #2
Figure 1.5 b on the seismogram (distance-time graph) can be used to calculate the wave’s speed.
The seismogram’s t gives the distance to the epicenter.
If we know the distance and speed, we can calculate the travel time.
The time of the Earthquake is equal to the arrival time MINUS the travel time.

32. Look at the Seismic Chart
Q. Does velocity increase or decrease over time? Why?
A. Velocity increases, because waves increase their speed as the rock density increases.

33. Behavior of Seismic Waves
1) The speed of a wave increases as the rock density increases (for a given temperature).
2) P waves (longitudinal) travel through solids and liquids.
3) S waves travel through solids only.

34. Evidence that Earth’s Has differentiated
1) We know the mass and volume of the Earth from geometric and astronomical considerations.
When we calculate the overall density (bulk density) we arrive at a value of 5.5 g/cm3.
But crustal rock is only 2.8 g/cm3…the material beneath the crust must be much more dense.

35. 2) We have known for a long time that the Earth has a magnetic field, and we have long assumed a massive source of iron is present in the Earth.

36. 3)  Iron meteorites have densities of 7.5 g/cm3, and provide analogies of the Earth’s interior.

37. 4. We gain most of our knowledge of Earth’s internal structure from studying earthquake waves.

38. The energy waves produced by earthquakes are called seismic waves.
Earthquake Waves
Earthquakes are sudden releases of energy caused by fault motion within the Earth.
The energy waves produced by earthquakes are called seismic waves.
Focus- The place where the fault motion occurred and where seismic waves are first generated.
Epicenter- The point on Earth’s surface directly above the focus.

39. Body Waves- Waves that travel through the Earth.
Two main types of seismic waves are generated during earthquakes: 1) body waves and 2) surface waves.
Body Waves- Waves that travel through the Earth.
P-waves: Waves that vibrate parallel to the vibrating source (travel fast).
S-waves: Waves that vibrate perpendicular to the vibrating source (slower).
Both P and S waves travel through solids.
A P wave will travel through liquids, but an S wave will not (you can’t shear a liquid).

40. Surface waves- Very slow moving waves that travel over the surface of the Earth. Surface waves cause the greatest damage to buildings and other structures. 

41. Earth’s Internal Structure: Evidence from Seismic Waves

42. V
E L O C I T Y
LITHOSPHERE
ASTHENO-SPHERE
DEEP INTERIOR
CRUST
MANTLE
OUTER CORE
INNER CORE