1. Inside Earth Chapter 2.2 Pages 64-70
Measuring
Earthquakes
Inside Earth Chapter 2.2
Pages 64-70

2. Fault
A break in Earth’s lithosphere (crust) where plates slide or move past each other.

3. Focus Focus: the starting point of an earthquake, usually underground
Depth of the focus is related to the type of boundary.
Transform: Shallow <300m
Divergent: 300m
Subduction: Deep 700m

4. Epicenter
The point directly above the focus on the surface of the Earth is called the Epicenter.

5. Seismic Waves
Vibrations caused by the energy of the earthquake that travel through the Earth’s interior and across the surface away from the focus
P-Waves
S-Waves
Surface Waves

6. Primary Waves First Wave to Arrive Passes through…
Squeeze and stretch rock, (Accordion-like)
Compression / tension stress
Passes through…
Solid rock
Magma
Ocean water
Air
Everything!

7. Secondary Waves Arrive second, after P-waves
Vibrate from side to side, up and down
Shake the ground back and forth
Can not pass through liquids or gasses
Indicates that Earth has a liquid outer core.

8. Surface Waves Travel along the Earth’s surface
Produced by P and S waves that reach the surface
Produce severe ground movement
Most damaging waves.

9. Seismograph
An instrument used to detect and record the seismic waves produced by earthquakes.

10. Seismograph Consists of a heavy weight attached to a frame by a wire.
A pen is attached to a heavy weight.
The pen stays in place, the drum moves during an earthquake.

11. Seismogram
The record sheet the pen records on as the drum rotates.

12. Seismograph More than 10,000 Stations Use Data to…
Determine an epicenter
Need 3 Stations
Earthquake Magnitude

13. Locating an Epicenter r
Need 3 Seismograph stations to determine their distance from the epicenter
Determine distance by:
D = S-wave arrival time - P-wave arrival time. r

14. Locating an Epicenter Each station draws a circle.
Where all three intersect is the epicenter.

15. Magnitude
The measure of the amount of energy released in an earthquake
Three types
Mercalli
Richter Scale
Moment Magnitude.

16. Mercalli Scale
12 steps describe how earthquakes effect people, buildings, and the surface
Rates earthquakes according to damage dealt to people and structures
Not a precise measurement.

17. Richter Scale Developed in the 1930’s by Charles Richter
Rates the size of the seismic waves.
Measures the intensity of ground movements
Provides accurate measurements for small, nearby earthquakes, but does not work well for large or distant.

18. Richter Scale

19. Richter Scale

20. Moment Magnitude Total Energy MM =
Indicates the total energy released during earthquake’s more accurately
Scale used by scientists
Can be used for any size earthquake, near or far.
Total Energy MM =

21. Moment Magnitude
Combines the following to determine the moment magnitude:
The type of seismic waves produced and their strength
How much movement occurred on the fault
Strength of the rocks that broke
5.0 Little damage
Above 5.0 major damage

22. Moment Magnitude

23. The point under the surface directly where the Earthquake originates is…
A. Fault
B. Seismic Waves
C. Earth’s Crust
D. Focus
E. Epicenter

24. The point on the surface above where the Earthquake originates.
A. Fault
B. Seismic Waves
C. Earth’s Crust
D. Focus
E. Epicenter

25. The wave that arrives first is the…
A. Secondary Wave
B. Seismic Waves
C. Sound Wave
D. Primary Wave
E. Tsunami Wave

26. The scale that measures the total energy released is the…
A. Richter Scale
B. Mecallie Scale
C. Bathroom Scale
D. Moment Magnitude
E. Magnitude

27. How many seismograph stations are needed to locate an earthquake?
B. 3
C. 1
D. 6
E. 4

28. What to Work On DUE: Friday, October 21st Read textbook pages 64-69
Answer the Section Review questions on page 69 (#’s 1-4)
DUE: Friday, October 21st

29. Locating an Epicenter Lab
Purpose: Geologists who study earthquakes are called seismologists. If you were a seismologist, you would receive data from all across the country. Within minutes after an earthquake, seismographs located in Denver, Houston, and Miami would record the times of arrival of the P waves and S waves. You would use this data to zero in on the exact location of the earthquake’s epicenter.

30. Locating an Epicenter Lab
Seismograph Data:
City
Denver, CO
Houston, TX
Miami, FL
Difference in P & S Wave Arrival Times
2min 10sec
4min
5min 40sec

31. Locating an Epicenter Lab

32. Locating an Epicenter Lab
(km)