1. 8.2 Measuring Earthquakes

2. 8.2 Measuring Earthquakes
Earthquake Waves
8.2 Measuring Earthquakes
 Seismographs are instruments that record earthquake waves.
 Seismograms are paper records of recorded ground motion made by seismographs.

3. 8.2 Measuring Earthquakes
 3 kinds of waves
• P waves
- Are push-pull waves that push (compress) and pull (expand) in the direction that the waves travel
- Travel through solids, liquids, and gases
- Have the greatest velocity of all earthquake waves
“P waves move through the entire earth- crust, mantle, and core) like a slinky”

4. 8.2 Measuring Earthquakes
Earthquake Waves
8.2 Measuring Earthquakes
• S waves
Shake particles at right angles to the direction that they travel
Travel only through solids
Slower velocity than P waves, but more destructive
“S waves move through the ground like a rope”

5. Seismic Waves Paths Through the Earth

6. 8.2 Measuring Earthquakes
3 Types of Waves
Surface waves – travel along Earth’s outer layer
8.2 Measuring Earthquakes

7. 8.2 Measuring Earthquakes
Locating an Earthquake
How far is your location from the epicenter?
8.2 Measuring Earthquakes
• Distance is found by the difference in the arrival times between P and S waves.

8. Locating an Earthquake
3 seismographs are required to correctly locate the epicenter of an earthquake
Epicenter is located where three circles intersect

9. 8.2 Measuring Earthquakes
Intensity – based on amount of damage
Richter scale – based on amplitude of largest seismic wave (outdated)
 Momentum Magnitude
• Measures very large earthquakes
• Moment magnitude is the most widely used measurement for earthquakes
Estimates the energy released by earthquakes.

10. Earthquake Magnitudes

11. Some Notable Earthquakes