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Fault lines evidence of old earthquakes

Posted on: March 29, 2008

The earthquake that severely damaged Wells, Nevada and shook Twin Falls in late February of this year served to remind us that we live in a part of the North American continent that is being stretched. The geological term is extension. The exact mechanism causing this to happen is unclear, but the result is that from the Sierras on the west to the Wasatch Front in Utah, the crust is being pulled like taffy. These two ranges may actually be hundreds of miles further apart than they were before the current period of extension began.

While the crust doesn’t thin to the extreme of taffy, it does stretch somewhat. However, at some point, the stress becomes too great, and the crust simply snaps, creating a fault line, and releasing the energy as an earthquake. The energy released is equal to that needed to cause the break.

Once a break has formed, later movement along the fracture will cause additional earthquakes as the two blocks slide against each other. Obviously, it’s easier for the crust to move along an existing break rather than to create a new one and so, sporadic movement may continue along an established fault line for a long period of time. The question asked by those who seek to protect the public from earthquake hazards is which faults will move? This is a topic for another time.

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Fault lines evidence of old earthquakes

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