Section 2: The Distribution of Earthquakes

Activity #3: DOES TOPOGRAPHY SIGNAL EARTHQUAKE POTENTIAL?

Concept: Topography -- mountains, hills, and basins, for example -- is generally the result of movement along faults. Many of these faults may be currently inactive, but all generated earthquakes in the past. Seismicity can typically be expected in areas of steep topography.

Materials:

Procedure:

In this activity, you will once again be studying the distribution of the epicenters of all earthquakes recorded between 1932 and 1996. This time, however, these epicenters will be shown against a background image of topography. Study the topographic image from Seismicity for 1932-1996. Epicenters are again shown by single red pixels, but fault traces are not shown, and other labelling is minimal, to keep the image as clear as possible. The epicenters can be "removed" by moving the mouse pointer off of the image.

Now consider these investigative questions:

  1. Southern California is a region with many steep and abrupt topographic changes. Some of these should be readily visible on the plot. Do these sudden topographic changes show a correlation with the seismicity?

  2. Linear topographic features, not necessarily associated with large elevation changes, can also be found in this area. Look for these linear (straight or smoothly-curving) features. Are these landforms associated with seismicity?

  3. Several areas with definite topographic changes are almost unmarked. How might these topographic changes be different from the others -- could they still be caused by faultng and tectonics?

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