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# Richter Scale Graphing

## Introduction:

The Richter Scale measures the magnitude (amount of motion) of an earthquake at the focus. Unlike most scales you've used, the Richter scale is not linear. On a linear scale, the distance between each tic mark represents an equal value. The Richter scale is logarithmic. On a logarithmic scale, the distances between tic marks DO NOT represent equal values. In other words, an earthquake that registers as a nine is NOT one time larger that an eight. To help you understand this idea, you'll be making a graph that clearly shows the relationship between the Richter Scale values and actual ground motion.

Richter Scale Value | Amplitude 100 km from Epicenter (millimeters) |
---|---|

2 | .00004 |

3 | .0004 |

4 | 0.004 |

5 | 0.04 |

6 | 0.4 |

7 | 4.0 |

8 | 40 |

9 | 400 |

- Study the data table on the right.
- Label the Richter Scale values on the x-axis. Your scale should start at 1 and end on the right at 9.
- Label the amplitude values on the y-axis of your graph. Your y-axis scale should start at 0 mm and go up to 400 mm.
- Graph the data points and then connect the points with a single smooth line. Make a big graph!
- Use the graph to help you answer the questions.

## Questions for Analysis

Answer the questions below in complete sentences where appropriate.

- Describe the shape of the curve on your graph.
- How many times GREATER is the motion experienced during a magnitude seven earthquake compared to a magnitude six?
- How many times GREATER is the motion experienced during a magnitude six earthquake compared to a magnitude five?
- How many times LESS is the motion experienced during a magnitude three earthquake compared to a magnitude four?
- On the Richter Scale, each increase in number value represents a _______ times increase in ground motion.
- How many times greater is the motion experienced during a magnitude nine earthquake compared to a magnitude seven?
- Estimate the magnitude for an amplitude reading of 20 mm.
- Estimate the amplitude reading for a magnitude 4.5 earthquake.
- Most people do not understand that an earthquake with a magnitude of seven is ten times greater than a magnitude six earthquake. Discuss how this might present a problem in getting people to prepare adequately for a large earthquake.