GL 107 Earth Systems Science

K. Hannula

Discussion questions for 10/1/07

1.  Explain the difference between earthquake magnitude and earthquake intensity.

Earthquake magnitude is based on seismogram records of the shaking during an earthquake.  Magnitude does not change with distance from the epicenter.  Magnitude is measured on the logarithmic Richter scale, or on a similar scale.

Earthquake intensity is determined from subjective human experiences and the amount of damage done by an earthquake.  (It includes descriptions such as "Not felt" or "Chimneys cracked.")  It is generally larger near the epicenter, and decreases with distance from the fault that slipped.  It is measured on the Modified Mercalli Intensity scale.

2.  How is the Richter scale magnitude of an earthquake determined?

1) Measure the amplitude (amount of shaking as recorded on a seismograph) of seismic waves.

2) Determine the distance from the epicenter, and correct for the distance.

3) Calculate magnitude on a logarithmic scale (equations aren't given in book, and aren't necessary).  (See Figure 7.12 on p. 198 in your textbook.)

3.  What are some potentially destructive effects of earthquakes?