1. 8.2 – Measuring Earthquakes – Part II

2. Do Now
What are the two different types of measurements to describe the size of an earthquake?

3. Do Now
What are the two different types of measurements to describe the size of an earthquake?
Intensity
Magnitude

4. Key Words
Intensity
Magnitude
Quantitative

5. Vocab Words
Moment Magnitude

6. Measuring Earthquakes
Historically, scientists have used two different types of measurements to describe the size of an earthquake – intensity and magnitude.

7. Intensity
Intensity is a measure of the amount of earthquake shaking at a given location based on the amount of damage.
Intensity is not a quantitative because it is based on uncertain personal damage estimates.

8. Magnitude
These are quantitative measurements that were developed relying on the calculations using seismograms.
Magnitudes are the measure of the size of the seismic waves or the amount of energy released at the source of the earthquake.

9. Earthquake Scales Richter Scale Moment Magnitude
Modified Mercalli Scale

10. Richter Scale
Based on the amplitude of the largest seismic wave. (P wave, S Wave or Surface Wave)
Does not estimate adequately the size of very large earthquakes.
This scale is very outdated
News reports may still use it, but scientists do not.
Only useful for small, shallow earthquakes within about 500 kilometers of the epicenter.

11. Richter Scale

12. Moment Magnitude
Derived from the amount of displacement that occurs along the fault zone.
Moment magnitude is the most widely used measurement for earthquakes because it is the only magnitude scale that estimates the energy released by earthquakes.
Measures very large earthquakes.

13. Moment Magnitude

14. Modified Mercalli Scale
Rates an earthquake’s intensity in terms of the earthquake’s effects at different locations.
The same earthquake can receive different Mercalli ratings at different locations.

15. Modified Mercalli Scale

16. Notable Earthquakes

17. Group Challenge Question
You are on a large ocean research ship. You have generated seismic waves by causing an explosion on a platform towed behind the ship. What seismic waves will be recorded by a seismograph located on the ocean floor beneath the ship? Explain your answer.