1. EARTHQUAKES! Video: Earthquakes 101
Chapter 12

2. Section 1
Earthquakes are caused by a sudden release of energy when rocks move along a fault.
Elastic rebound is thought to cause the rocks to move.

3. Anatomy of an Earthquake
Focus-location of first motion in Earth
Epicenter-spot on surface above the focus
The focus can be shallow or deep
Shallow foci cause the most damage

5. Seismic Waves Body Waves: Travel through the Earth Made up of:
-P waves: primary, fastest
-S waves: secondary, second fastest, travel through solids only

6. Earthquake Waves & Earth’s Interior

7. Seismic Waves and the Earth’s Interior
The speed and direction of seismic waves gives us information about the Earth’s structure
Waves travel at different speeds through different materials
Shadow Zones-areas where no body waves are detected

8. Comparing Seismic Waves

9. Seismic Waves (cont) Surface Waves Slowest moving waves
May cause the greatest damage
2 Types:
-Rayleigh
-Love

11. Earthquakes and Plate Tectonics
Most earthquakes occur at plate boundaries (converging and diverging) where the stress is the greatest

12. How Seismographs or Seismometers Work, TB pg. 217
-measures ground motion and can be used to
determine the distance seismic waves travel

13. They use the lag time to calculate a distance to the epicenter
How do scientists calculate how far a location is from the epicenter of an earthquake?
Scientists calculate the difference between arrival times of the P waves and S waves (lag time)
The further away an earthquake is, the greater the time between the arrival of the P waves and the S waves
They use the lag time to calculate a distance to the epicenter

14. Typical Seismogram- a graphical illustration of EQ waves

15. Locating Earthquakes

16. Locating Earthquakes

17. Locating Earthquakes

18. Section 2 Seismographs record vibrations in the ground
Magnitude: the strength of an earthquake, Richter scale or moment magnitude (more accurate)
Intensity (amount of damage)-modified Mercalli scale-from I-XII, oldest measurement scale

19. How are Earthquakes Measured? Richter Scale

20. How are Earthquakes Measured? Mercalli Intensity Scale
Click on the picture for a video clip
Or Simulator link

21. Predicting Earthquakes-video clip: https://www. youtube. com/watch
No reliable way to predict earthquakes: scientist use the following information
Scientists are trying to detect changes that occur before an earthquake
Seismic gaps are areas of low earthquake activity, but have a history of strong activity-might be spot for future earthquake
Foreshocks-small earthquakes that precede a large earthquake

22. Soil Type *Type A having the least amplification and Type E the most.
Type of soil can affect how a building responds to seismic waves.
NEHRP has defined six different soil and rock types based on their shear-wave velocity, in order to determine amplification effects:
Type A, hard rock (igneous rock).
Type B, rock (volcanic rock).
Type C, very dense soil and soft rock (sandstone).
Type D, stiff soil (mud).
Type E, soft soil (artificial fill).
*Type A having the least amplification and Type E the most.

23. Section 3 Video: Tsunamis 101
Tsunamis can form when the epicenter is on the ocean floor
Damage to structures depends on how they are built and what type of ground they sit on