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. Seismograph

4. Seismogram
Fastest waves
Slowest waves and most destructive

5. 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”

6. 8.2 Measuring Earthquakes
Earthquake Waves
8.2 Measuring Earthquakes
• S waves
Seismic waves that travel along Earth’s outer layer
- Shake particles at right angles to the direction that they travel
- Travel only through solids
- Slower velocity than P waves
“S waves move through the ground like a rope”

7. Seismic Waves Paths Through the Earth

8. 8.2 Measuring Earthquakes
Locating an Earthquake
How far is your location from the epicenter?
8.2 Measuring Earthquakes
• Distance from you to epicenter is found by the measuring difference in the arrival times between P and S waves.

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

10. 8.2 Measuring Earthquakes
 Momentum Magnitude
• Moment magnitude is the most widely used measurement for earthquakes
Estimates the energy released by earthquakes.
• Measures very large earthquakes

11. Earthquake Magnitudes

12. Some Notable Earthquakes

13. Modern Earthquakes 7.2 Turkey in 2011 572 deaths
9.0 Japan in deaths