1. Your questions… and (some) answers

2. Q: What causes earthquakes? A: After yesterday’s stations, you should be able to explain this in your own words. Write down your explanation in your notebook. (2 minutes) When you are done, share with your partner. (1 minute) Then we will share as a class. (2 minutes) mantle convection Wave propagation, Conservation of energy

3. Q: What was the largest earthquake ever? A: That depends what you mean by largest. If you mean the greatest amount of energy recorded in an earthquake, the answer is the 1960 earthquake in Chile, South America. It registered at 9.5 on the Richter scale. The damage reached as far as Hawai`i, the Philippines, California, and Japan. However, “only” about 1,655 people perished. This picture shows the path of the resulting tsunami. A tsunami is a shear wave (S-wave, or transverse wave) moving through the ocean.

4. Q: What was the largest earthquake ever? A: That depends what you mean by largest. If you mean the most number of people killed in an earthquake, the answer is the earthquake in Shaanxi, China, in 1556. Primary sources estimated around 830,000 casualties. However, analyses of the geologic record suggest that the magnitude of this earthquake was “only” about 8.0. Why do you think this less-powerful earthquake killed so many more people?

5. Q: How are earthquakes measured? A: With seismometers.

6. Q: How are earthquakes measured? A: Before 1932, there was no objective (quantitative) scale for rating earthquakes. Ratings were based on subjective (qualitative) observations.

7. Q: How are earthquakes measured? A: Charles Richter, a seismologist living in California, developed the Richter magnitude scale in the 1930s. It is a logarithmic scale, like the pH scale for acids and bases. A magnitude of 1.0 really means 10 1 or 10 micrometers on the seismograph. A magnitude of 2.0 means 10 2 or 100 micrometers. A magnitude of 3.0 means 10 3 or 1,000 micrometers (1 millimeter). Each whole number magnitude is ten times as powerful as the previous number.

8. Q: How often do earthquakes occur? A: Again, that depends. Large earthquakes are relatively rare – the larger the earthquake, the less likely it is to happen. Small earthquakes (magnitude ≤2.0) occur everyday, but they are generally too small for humans to feel and they do not damage buildings. This relationship is called a power law.

9. Q: How often do earthquakes occur? A: Power laws describe earthquake frequency. They also describe the frequency of all kinds of other natural phenomena, from the internet to city populations and more. Scientists are not really sure what makes power laws such a common occurrence in the natural world. “Normal” distribution, or “Bell curve” Power law distribution magnitude magnitude (or rank) frequency What kinds of things do you think might have a normal distribution, with most values clustered around the mean, and about equal numbers of low and high values? What kinds of things do you think might have a power law distribution, with most values very low, and extremely high values occurring very rarely?

10. “Normal” distribution, or “Bell curve” Power law distribution magnitude magnitude (or rank) frequency Examples: Heights of people Weights of people Heights and weights of almost any organism Speed of traffic Standardized test scores (and most grades) Others? Examples: Income of people Size of cities Frequency of words Sales of bestselling books Sizes of earthquakes Stock market fluctuations Others?

11. Q: Are earthquakes preventable? A: What do you think? You now know what causes earthquakes. Could humans control these processes? Write down your answer in your notebook. (2 minutes) When you are done, share with your partner. (1 minute) Then we will share as a class. (2 minutes)